Cell structures and functions

serve as structural components of cell membranes, function as energy storehouses, and function as important signaling molecules

includes

group of polar lipids that consist of two fatty acids

they are hydrophobic and insoluble in water

and

provide energy for living organisms, insulate body organs, and transport fat-soluble vitamins through the blood.

formed when the three hydroxyls (OH-) groups of a single glycerol molecule react with the carboxyl group (COOH-) of three fatty acids by forming ester bonds.

the building blocks of the fat in our bodies and in the food we eat

a clear, colourless, viscous, sweet-tasting liquid belonging to the alcohol family of organic compounds

primary role of carbohydrates is to supply energy to all cells in the body.

examples of different types

are those carbohydrates that on hydrolysis with acids or enzymes give two molecules of monosaccharides which can either be the same or different.

types

Lactose

a disaccharide sugar synthesized by galactose and glucose subunits

sucrose

a disaccharide made up of 50% glucose and 50% fructose

maltose

a product of the breakdown of starches during digestion, consists of two molecules of glucose connected via an α-linkage

simple sugars, are the simplest forms of sugar and the most basic units from which all carbohydrates are built

types

Glucose

It is an important and quickly mobilized source of stored glucose.

fructose

a member of a group of carbohydrates known as simple sugars, or monosaccharides. Fructose bonded with glucose, another monosaccharide, forms sucrose, or table sugar.

galactose

are polymeric carbohydrates composed of long chains of monosaccharide units joined by glycosidic linkages

types

Starch

Amylopectin

Is a polymer of glucose or polysaccharide formed by plants as an energy storage molecule

Amylose

Another type of polysaccharide molecule produced by plants, is a more linear molecule with fewer branched bonds.

Glycogen

A form of glucose, a main source of energy that your body stores primarily in your liver and muscles. Glycosidic bonds are also used to link polysaccharides.

Glycosaminoglycans

Also known as mucopolysaccharides, are negatively-charged polysaccharide compounds.

Cellulose

The main substance found in plant cell walls and helps the plant to remain stiff and strong. polysaccharides generally perform one of two functions: energy storage or structural support, therefore use cellulose as linear polymers that are used for structural support in plants and animals.

Inulin

Inulin is a fructan polysaccharide found in many different types of plants

large biomolecules that play essential roles in all cells and viruses. A major function of nucleic acids involves the storage and expression of genomic information.

different types

Nucleosides are the structural subunit of nucleic acids such as DNA and RNA.

consist of

AGGTU

ATP

ribose

RNA

deoxyribose

DNA

the basic building block of nucleic acids (RNA and DNA).

Nucleotides are composed of phosphoric acid, a pentose sugar (ribose or deoxyribose), and a nitrogen-containing base.

A nucleotide is composed of a nitrogenous base, deoxyribose, and at least one phosphate group.

serve as transporters, moving nutrients and other molecules in and out of cells, and as enzymes and catalysts for the vast majority of chemical reactions that take place in living organisms.

proteins are made up of

Amino acids are molecules that combine to form proteins. When proteins are digested or broken down, amino acids are left.

the sequence of amino acids linked together to form a polypeptide chain.

bonds formed are

a chemical bond formed between two molecules when the carboxyl group of one molecule reacts with the amino group of the other molecule

The most common types of secondary structures are the α helix and the β pleated sheet.^

Both structures are held in shape by

form between

primarily due to interactions between the R groups of the amino acids that make up the protein.

bonds formed are

water fearing, non-polar

is a covalent bond between two sulfur atoms

the association of several protein chains or subunits into a closely packed arrangement.

held together by non covalent bonds

type of linkage formed from the electrostatic attraction between oppositely charged ions in a chemical compound.

result from fluctuations in charge density of particles.

Made up of a phospholipid bi-layer, which consists of a hydrophilic head and hydrophobic tail

Depending on the phase transition temperature the membrane can either be fluid (where stuff can pass through easily) or rigid (where it is much more difficult for certain things to pass through). Unsaturated hydrocarbon tails = fluid while saturated hydrocarbon tails = rigid

Membrane Proteins^

Certain proteins help to transport certain solutes in an out of the cell, while others even change shape through the usage of ATP to allow only the transfer of certain molecules inside the cell.

Some proteins are enzymes that will help convert certain molecules so that they are able to either be used by the cell itself or possibly another type of cell

Some proteins are receptors that interact with signaling molecules such as hormones that will then relay that same information to the rest of the cell.

Some proteins are also used as a form of identification by other cells.

Certain proteins are used to join cells together through gap junctions or tight junctions

Certain proteins are used to attach to the cytoskeleton and ECM allowing the proteins to coordinate extracellular and intercellular changes

Selective Permability

Membrane only allows certain small non polar(O2, CO2) and uncharged polar molecules(H2O, glycerol) to pass through, large uncharged polar(Sucrose and glucose) molecules and Ions (Na+ K+) require the usage of a protein to pass through.

Non Polar

Any R group ending in CH or a 6 ringed carbon hexagon

Polar

Any R group ending in OH, SH, O, or NH2

Acidic

Any R group ending in o- causing the amino acid to have an overall negative charge

Basic

Any R group ending in a NH+, NH2+ Or NH3+ causing the overall charge of the amino acid to be positive

Active Transport

Movement from a low concentration to a high one through the usage of energy

Sodium-Potassium Pump

Starts off by bringing Na+ in then once a large amount is inside it starts to release Na+, and for every three Na+ it brings out 2 K+ molecules come in, going against the concentration gradient

Proton Pump

Uses ATP to transfer H+ from a low concentration gradient to a high concentration gradient

Cotransport

When the transport of a solute from a low to high concentration also indirectly transfers another substance

Gated Ion Channels

Stretch Gated

Ion gate opens only when membrane is deformed and will open up as a response to the stimuli

Ligand gated

Ion gate opens up in response to when a Neurotransmitter binds to the channel

Voltage Gated

Ion channel opens or closes depending on the membrane potential

Passive Transport^

Diffusion across the cell membrane with no energy usage

Diffusion

Movement of certain molecules from a high to low concentration until they reach an equilibrium

Osmosis

The diffusion of water from a concentration that has a low concentration of solute to the side that has a high concentration of solute until an equilibrium is reached

Water Balance

Isotonic

Solute concentration is the same inside and outside of cell so no water movement

Hypotonic

Cell has a greater solute concentration that outside so the cell starts to gain water

Hypertonic

The cell has a smaller solute concentration than outside so the cell starts to lose water

Facilitated Diffusion

Passive transport through the usage of proteins

Channel Protein

Channel proteins have a channel that allow solutes or other water molecules to pass through

Carrier Protein

Carrier proteins open up to intake certain molecules and then open back up to release them (pac-man)

Ungated Ion channel

Ion channel that lets ions just flow in and out of the cell from High to low concentrations

Nucleoid

The nucleoid is the region of cytoplasm in prokaryotic cells that holds the chromosome with most or all of the cell's genetic material.

Pili

The pili are structures on the surface of prokaryotic cells that are short and hair-like. Their role is to mate with other cells.

Fimbriae

Hairlike appendages that are typically shorter and more numerous than pili, and are used as a means for prokaryotes to stick to their substrate or to each other.

Capsule

The capsule is a sticky outermost layer that is made of polysaccharides or proteins and exists to help bacteria stick to organisms or surfaces. It also protects the bacteria from phagocytosis and dehydration.

Cell Wall

In plants and fungi (eukaryotes), the cell wall is made up of cellulose or chitin. In bacteria, it is made of the polymer peptidoglycan, but archaeal cell walls do not contain peptidoglycan, they only contain proteins and other polysaccharides. No matter what it is made of, the cell wall has the same purpose in every cell which is to provide structure and support, as well as to act as a semi-permeable surface to allow molecules to enter and exit the cell.

Plasma Membrane

In both prokaryotic and eukaryotic cells, the plasma membrane is made of a phospholipid bilayer embedded with proteins, but the lipids are negatively charged in prokaryotic plasma membranes while the lipids in eukaryotic plasma membranes are neutral. This difference is due to the fact that the plasma membrane in prokaryotes carries out all the functions that are done by the plasma membrane and the membrane-bound organelles of eukaryotes. Functions that are similar between the two are separating the cytoplasm from the cell's outside environment and controlling the passage of molecules that go in and out of the cell.

Cytoplasm

The cytoplasm is a gel-like fluid that is enclosed by the plasma membrane and is separate from the nucleus of eukaryotic cells. It functions as a medium for chemical reactions to take place inside both prokaryotic and eukaryotic cells.

Genetic Material

The genetic material (DNA) floats freely throughout prokaryotic cells which only have a singular chromosome in the nucleoid, while the DNA in eukaryotic cells is enclosed in a membrane-bound nucleus which contains multiple chromosomes. DNA itself is composed of building blocks called nucleotides, which are composed of a phosphate group, a deoxyribose sugar and a nitrogenous base. The role of DNA is storing information necessary to cell replication, mutation and gene expression.

Ribosomes

Ribosomes in prokaryotes are smaller than those in eukaryotes (70S vs 80S). Prokaryotic ribosomes are made of a 50S large subunit and 30S small subunit, while eukaryotic ribosomes are made of a 60S large subunit and 40S small subunit. The large subunit in prokaryotic ribosomes is made up of two rRNA molecules, 23S rRNA and 5S rRNA, while the large subunit in eukaryotic ribosomes is made up of three rRNA molecules, 28S rRNA, 5.3S rRNA and 5S rRNA. Both prokaryotic and eukaryotic ribosomes are composed of rRNA and ribosomal proteins, but prokaryotic ribosomes are 60% rRNA and 40% ribosomal proteins while eukaryotic ribosomes are 40% rRNA and 60% ribosomal proteins. Ribosomes in prokaryotic cells are scattered freely throughout the cytoplasm and even though eukaryotic cells also contain free ribosomes, most of their ribosomes are attached to the outer surface of their nucleus and endoplasmic reticulum. In both prokaryotic and eukaryotic cells, the ribosomes are the site of protein synthesis.

Flagella

Flagella are structures that can be scattered throughout the surface of cells or collected at one or both ends of the cell. In both prokaryotes and eukaryotes, flagella are made of proteins, but the proteins that make them up are completely different from each other in prokaryotes and eukaryotes. Additionally, flagella in bacteria and archaea are also made of completely different proteins. Flagella in prokaryotes are about a tenth of the width of flagella in eukaryotes. However, despite their structural differences, they all serve a common purpose which is cell mobility.

Structure

Phospholipids are composed of a hydrophilic (polar) phosphate head and two hydrophobic (nonpolar) hydrocarbon tails connected by glycerol.

Function

The structure of phospholipids allows them to form bilayers where their hydrophilic heads face outside and their hydrophobic heads face inwards to avoid water. These phospholipid bilayers are what make up the plasma membrane of cells, and they are mostly held together by hydrophobic interactions. Phospholipids are essential to membrane fluidity in that membrane fluidity will depend on the properties of the phospholipids. If the phospholipids have mostly unsaturated hydrocarbon tails, the kinks in the tails caused by their double bonds will prevent the phospholipids from being able to pack together as closely as phospholipids with saturated hydrocarbon tails, increasing membrane fluidity. Other factors that affect membrane fluidity are temperature and cholesterol. Lower temperatures decrease membrane fluidity unless cholesterol is present. If cholesterol is present, membrane fluidity will increase at lower temperatures and decrease at higher temperatures. This is because cholesterol limits phospholipids from becoming closely packed together which prevents the solidification and retains the fluidity of the membrane. In the case of higher temperatures, cholesterol restricts phospholipid movement and therefore decreases membrane fluidity.

Nucleus: Holds the majority the cell's genes

Nuclear Envelope

The nuclear envelope encloses the nucleus and separates it from the cytoplasm. It is a double membrane, with each membrane consisting of a lipid bilayer and proteins. This envelope also has pores that are lined by protein structures called pore complexes that control the entrance and exit of macromolecules, proteins and RNA.

Chromatin

Chromatin is a material made of DNA and proteins. It is the material that makes up a cell's chromosomes.

Nucleolus

The nucleolus is a nonmembranous structure composed of DNA, RNA and proteins. It works to produce the cell's ribosomes.

Mitochondria

Mitochondria are made up of two membranes composed of phospholipid bilayers and proteins. Their function is to perform cellular respiration, the process of producing ATP from food brought into cells.

Golgi Apparatus

The Golgi apparatus is made up of stacks of flattened membranous sacs called cisternae, as well as transport vesicles that travel between the Golgi and other organelles. The cisternae in the Golgi are not physically connected like they are in the ER. Golgi stacks have two different sides, a cis face that is typically located closer to the ER and a trans face where vesicles are released to travel off to different sites. The role of the Golgi apparatus is to modify materials it receives from the ER and sent the materials to other organelles or out into the cytoplasm.

Endoplasmic Reticulum (ER): A network
of membranous tubules and sacs called
cisternae that is continuous with the nuclear envelope. The ER is separated into two regions: the smooth ER and the rough ER.

Smooth

The smooth ER region is called this way because it does not
contain ribosomes. It has many functions in metabolic processes, such as using its enzymes to synthesize lipids and to detoxify drugs and poisons, as well as storing calcium ions.

Rough

The rough ER region gets its name from the fact that it is covered in ribosomes. It secretes proteins that are bonded to carbohydrates, structures which are called glycoproteins. It also uses its enzymes to create membrane phospholipids, and it adds membrane proteins and phospholipids to its own membrane in order to grow. Its membrane is held together by hydrophobic sections.

Lysosomes

Lysosomes are membranous sacs of hydrolytic enzymes.
The enzymes themselves are nearly neutral, but lysosomes are acidic in order to aid in intracellular digestion by using its enzymes to digest food and produce nutrients for the cell such as sugars and amino acids.

Chloroplasts

Similar to mitochondrion, chloroplasts are also made of two
membranes as well as internal membranous sacs, but they only appear in plants. These internal membranous sacs are called thylakoids, and some of these thylakoids appear in stacks called grana. The stroma is the fluid outside of the thylakoids, and it contains enzymes, ribosomes and the DNA of the chloroplast. All of these components of chloroplasts function together to perform photosynthesis.

Cytoskeleton: A network of fibers extending throughout the cytoplasm

Microtubules

Microtubules are larger in diameter than both microfilaments and intermediate filaments. They are hollow rods made of a globular protein called tubulin. Tubulin is a dimer consisting of the alpha and beta tubulin polypeptides. The microtubules provide the cell with shape and support, in addition to acting as a track where organelles with motor proteins can move throughout. They also play a role in separating chromosomes during cell division.

Centrosome

The centrosome is a region located near the nucleus, and it is the main site of microtubule assembly.

Intermediate filaments

Intermediate filaments are wider in diameter than microfilaments but smaller than microtubules. They are made of fibrous proteins coiled into cables, and their function is in maintaining the cell's shape, anchoring the nucleus and other organelles, as well as forming nuclear lamina.

Microfilaments

Microfilaments are smaller than both microtubules and intermediate filaments. They are made up of two intertwined strands of actin, and they work in maintaining cell shape, contracting muscles, changing cell shape, aiding in cell motility as well as cytoplasmic streaming in plant cells and cell division in animal cells.

Plasmodesmata

The plasmodesmata are only found in plants; they are membrane-lined channels filled with cytosol that connect cells into a continuous structure where water and small solutes can travel freely throughout, as well as some proteins and RNA molecules.

Peroxisomes

Vacuoles: large vesicles derived from
the ER and Golgi

Animal Cell Vacuoles

Vacuoles in animal cells are small, membrane enclosed
structures that function with lysosomes to digest food brought into the cell.

Plant Cell Central Vacuole

Mature plant cells typically have one large central vacuole
which absorbs water to support the growth of the cell and contains a solution called cell sap which acts as a receptacle for inorganic ions like potassium and chloride.

Animal Cell Junctions: All are composed
of epithelial tissue

Gap Junctions

Gap junctions are made of membrane proteins that create
space for small molecules to pass, and they are crucial to cell communication.

Tight Junctions

Tight junctions use proteins to bind plasma membranes of cells to each other so no fluids can pass between the cells.

Desmosomes

Desmosomes attach cells to each other sturdily and are held in the cytoplasm by intermediate filaments made of keratin proteins.

takes place in the chloroplast

includes

uses

the energy storage molecule

the reduced electron carrier

takes place

of organelles called

Large protein and pigment complexes that are specially designed to gather light are essential for the light reactions.

two types of photosystems

The electron arrives at photosystem I and joins the P700 pair of chlorophylls in the reaction center. The electron in P700 is then raised to an extremely high energy level and transmitted to an acceptor molecule when light energy is absorbed by pigments and sent inward to the reaction site.

Energy is transferred from pigment to pigment inside of photosystem II when light is absorbed by one of the numerous pigments inside. This process continues until the reaction center is reached. An electron's energy is raised there, where it is transmitted to P680. An acceptor molecule receives the high-energy electron.

releases

start in

the high energy electron is transferred through ETC and then at the end of the chain the electron is passed to NADP+ to make NADPH

pumps H+ ions into thylakoid

H+ then activates

As it moves through an electron transport chain, the high-energy electron expends energy. A gradient is created when some of the energy released causes the pumping of ions from the stroma into the interior of the thylakoid.

then

H+ ions flow down their gradient and into the stroma, they pass through ATP synthase, driving ATP production

a process known as

where sugar is synthesized

takes place

Cells and tissues that support and give structure to organs, glands, or other tissues in the body.

this forms

splits to form 2 molecules of

This reaction is catalyzed by the enzyme RuBP carboxylase/oxygenase, or rubisco

3-PGA molecules

uses

to convert 3-PGA molecules into molecules of

produces

Some G3P molecules go to make glucose, while others must be recycled to regenerate the RuBP acceptor.

requires

and involves

A process where plants use sunlight to make food from water and carbon dioxide

Glycolysis: First stage of cellular respiration (takes place in the cytosol)

Key Steps

Step 1: Hexokinase transfers a phosphate group from ATP to glucose, making it more chemically reactive. The charge on the phosphate traps the sugar in the cell.

Step 3: Phosphofructokinase transfers a phosphate group from ATP to the opposite end of the sugar, using a second molecule of ATP.

Input

1 Glucose

2 NAD+

2 ATP

Output

2 Pyruvate

2 NADH

4 ATP

Formed through substrate level phosphorylation

Net

2 Pyruvate

2 NADH

2 ATP

Pyruvate Oxidation (starts in the cytosol and moves to the mitochondrial matrix)

Input

2 Pyruvate

2 CoA

2 NAD+

Output

2 Acetyl CoA

2 NADH

Net

2 Acetyl CoA

2 NADH

Krebs Cycle/Citric Acid Cycle (takes place in the mitochondrial matrix)

Key Steps

Step 1: Acetyl CoA adds its two-carbon group to oxaloacetate, forming citrate.

Step 3: Isocitrate forms alpha ketoglutarate through an oxidation-reduction reaction.

Input

2 Acetyl CoA

6 NAD+

2 FAD

Output

6 NADH

2 FADH2

2 ATP

Formed through substrate level phosphorylation

Net

6 NADH

2 FADH2

2 ATP

Oxidative Phosphorylation

Electron Transport Chain (ETC))

The electron transport chain is a series of molecules found in the inner membrane of the mitochondria in eukaryotes, and found in the plasma membrane of prokaryotes. Most of the chain consists of proteins with electron carriers that exist in multiprotein complexes numbered I through IV. In this chain, electrons from either NADH or FADH2 move down the chain through increasingly electronegative carriers in a series of oxidation-reduction reactions. The electrons are transferred to oxygen at the end of the chain, and this oxygen forms water by splitting in half and taking up H+. The transport of electrons and pumping of protons create an H+ gradient across the membrane. This whole process releases an abundance of free energy which is coupled with chemiosmosis to synthesize ATP.

Chemiosmosis

The free energy released from the ETC is used to pump H+ ions from the mitochondrial matrix to the intermembrane space, creating an electrochemical gradient. The flow of H+ ions down this gradient and back to the mitochondrial matrix synthesizes ATP due to the passing of the H+ ions through the enzyme ATP synthase. When H+ ions flow down their electrochemical gradient, ATP synthase turns like a waterwheel, catalyzing the addition of an inorganic phosphate to ADP in order to form ATP.

Input

O2

10 NADH

2 FADH2

Output

H2O

26-28 ATP

Formed through the coupling of chemiosmosis with the ETC

Net

H2O

26-28 ATP

Local signalling

Paracine Signalling

Secreting cell releases ligand/a signal to target cell receptor in its local area

Synaptic Signalling

Electrical signal along nerve cell causes the release of neurotransmitters that diffuses across synapses into target cell receptors

A stimulus that is strong enough to cause depolarization will result in triggering an action potential

If the target cell is too far away a cell may use a medium like a blood vessel to transport signals like hormones across the body to target cells receptors

Physical Contact

Cells communicate through physical touch through the use of junctions allowing molecules to transfer or proteins to bind

Gap Junctions are in animal cells

Plasmodesmata are in plant cels

Receptor

Used with small non polar molecules and hormones that can easily bypass the membrane and bind to the receptor inside the cell

steps

Hormone/nonpolar molecule passes through the plasma membrane

The hormone/nonpolar molecule then binds to the receptor inside the cell activating it and becoming a receptor complex inside the cytoplasm

The receptor complex then enters the nucleus and binds to specifics genes

The bound proteins is then used as a transcription factor transcribing the gene into mRNA

Finally, the mRNA is translated into a specific protein

Used with larger hydrophilic polar molecules that can't enter the inside of the cell so they bind to the receptor on the outside of the cell.

steps

Reception

Transudction

Response

G protein

steps

G protein is bound to GDP making it inactive

Signalling mollecule binds to GPCR which allows for G protein to bind to it and caused GDP to be replaced with GTP

The now activated G protein can now travel and activate a nearby Enzyme triggering a cellular response

G protein then removes phosphate group from GTP making it once again GDP deactivating the G protein

Tyrosine Kinase

kinase help remove phosphate groups from ATP and add them to proteins

steps

Made up of two polypeptides that when a signal molecule is added to each of them dimerize

Each polypeptide functions as a kinase and adds phosphate groups from ATP to the other polypeptide (autophosphorylation)

When a total of 6 phosphate groups have been added with three on each polypeptide the tyrosine-kinase if fully activated

Now the receptor can bind to other proteins to create a cellular response in the cel

Phosphorylation Cascade

a type of signal transduction pathway that uses kinases and phosphates.

A signal molecule attaches to a receptor which in turns activates a relay molecule

The relay molecule activates the first protein kinase

The protein kinase then activates a different kinase

The first kinase has its prostate groups removed by a phosphatase

And then this process repeats until a kinase adds a phosphate group to a protein activating it and bringing a cellular response

The cellular response can either be the synthesis of enzyme or other proteins, by turning genes off and on

Second Messengers are relay molecules which carry the message from the first signal inside the cell

steps

A type of second messenger Synthesized from ATP using Adenylyl Cyclase^

cAMP binds to another kinase activating it

cAMP is then converted to AMP by Phosphodiesterase

Ion channell Receptor

An ion channel receptor acts as en entrance for ions.

steps

An ion channel remains closed until a signaling molecule binds to it

When the ion channel opens up only certain molecules are allowed through such as Na+ or Ca+

Finally when the signaling molecule leaves the ion channel closes along with it

Alcohol Fermentation

Process

Carbon dioxide is released from pyruvate which is converted into acetaldehyde. The acetaldehyde is then reduced by NADH to ethanol, regenerating the NAD+ necessary for glycolysis to keep occurring.

Input

2 NADH

2 Pyruvate

Output

Ethanol

NAD+

Lactic Acid Fermentation

Process

Pyruvate is directly reduced by NADH to form lactate with no release of carbon dioxide involved.

Input

2 NADH

2 Pyruvate

Output

Lactate

NAD+

involves

consist of

has

growing polypeptide

exit site

starts on

enter

a collection of organelles and membranes in eukaryotic cells that collaborate to transport, package, and alter lipids and proteins.

with the help of

(signal recognition particle and is made of RNA and protein)

then proteins are escorted to the

Here, several carbohydrate groups are added by enzymes in the ER to this protein now its called a glycoprotein

From the ER, the protein is shipped through a vesicle to the

Proteins and lipids go through further changes as they go through the Golgi.

then the proteins can be transported to the

stay as

Membrane protein

be secreted out of the cell

synthesis completes on free ribosomes which lead proteins to organelles like :

Structure

A polymer made up of monomers called nucleotides which are connected through phosphodiester bonds. RNA is also composed of nucleotides linked by phosphodiester bonds.

Replication

It was determined by Messleson and Stahl’s experiment that DNA replicates semiconservatively, meaning that the daughter molecules of a parent DNA molecule will each have one strand from the parent molecule and one newly made strand.

Prokaryotes

Site of transcription: Cytoplasm

Initiation

RNA polymerase binds to the template strand’s promoter sequence.

Elongation

RNA polymerase moves along the template strand of DNA, adding ribonucleotides in the 3’ to 5’ direction.

Termination

RNA polymerase reaches the template strand’s terminator sequence, stopping transcription and releasing mRNA that needs no additional alterations unlike in eukaryotes.

Eukaryotes

Site of transcription: Nucleus

Initiation

Proteins called transcription factors bind to the template strand’s promoter sequence, and RNA polymerase II binds the promoter.

Elongation

RNA polymerase II moves along the template strand of DNA , adding ribonucleotides to the 3’ end of the growing strand of RNA.

Termination

RNA polymerase II reaches the terminator sequence, stopping transcription and releasing pre-mRNA.

RNA processing

The pre-mRNA ‘s 5’ end gets a cap and its 3’ end gets a polyA tail which is added by polyA polymerase. Then spliceosomes are used to remove the pre-mRNA’s introns and splice together its exons, forming mRNA.

Eukaryotes

Most gene regulation occurs at the transcription level as there is no need to from pre mRNA if no protein is needed

Transcription factors

Proteins that bind to the promoter and are crtical for gene expression and regulation

Specific

Transcription factors that bind to distal control elements which are called enhancers, which can be either close to t

Activators

proteins that comes from cell signaling which increases levels of transcription

DNA Bending protein

brings the bound activators closer to the promoter, which results in the activator binding to certain mediator proteins forming an active transcription complex on the promoter

Repressors

Reduce levels of transciption

General

Transcription factors that bind to the proximal control elements on or near the promoter, resulting in basal/background level of transcription

Prokaryotes

Like Eukaryotes most gene regulation occurs at the transcription level

Operons

A segment of DNA positioned within the promoter that turns on gene expression or turns it off

Positive Regulation

Whenever an Acitvator binds to a Operator resulting in turning the gene ON and creating a high level of gene expression

Negative Regulation

When a repressor binds to a Operator causing the gene expression to be OFF (or basal).

Lactose

when lactose is used as an energy source Permease, a protein, will transfer the lactose while B-Galactosidase will break the glycolosidic linkage forming glucose an galactose

Lac Operon

When Lactose is present the transcription of LacZ, LacY, and LacA is blocked, so the repressor is able to bind to the operator and the operon is OFF

When glucose is present the lac operson is off due to glucose blocking Adenyl Cyclase

When lactose is present the repressors binds to it instead of the operator resulting in RNAP being able to bind to the promoter, through the activator protein CAP which is activated through cAMP that is formed from adenyl cyclase-Operon ON

When ON the mRNA is transcribed and translated to form 3 proteins, B-Galactosidase, Permease, and Transacetylase which all help break down lactase

Prokaryotes

Occurs at the same time as transcription

Eukaryotes

Occurs at different times compared to transcription

tRNA

tRNA going in the 3-5 directions binds to mRNA going in the 5-3 direction through the use of an anti codon and binds to the small ribosomal unit

Aminoacyl tRNA

add amino acid to tRNA

Large ribosomal unit

The start codon binds to the anticdodon in the p site, another trna then binds to the mRNA in the A site, then the p site trna moves to the e site and exits the ribosomal complex after losing its amino acid

Pepitdeyl Transferase

Add polpeptide bonds to amino acids to join them together

termination

When the stop codon reaches the a site a realease factor helps the ribsomola complex break apart and stops translation

Nucleosome

DNA wraps around a histome core twice forming a Nuclesome

Histome Core

A histome core is composed of multiple proteins which consist of H2A, H2B, H3, H4 with the H1 being on the outside of the core

H1

The H1 protein help the DNA wind even tighther together and eventually this winding results in the formation of a chromosome