Lac Operon
always off
by default
disaccharide, its digestive,
lactose breaks down to glucose
and galactose
example of both
positive and negative
regulation
organization of
lac operon
DNA
regulatory sequences
promoter for regulatory
gene (pi)
regulatory gene (f)
codes for repressor
protein
promoter for structural genes (Plac)
Operator
RNA polymerase
when RNA can bind
lactose available, low glucose
if glucose is scarce, the high level of cAMP activated CPR, which binds to the promoter and increases RNA polymerase binding there. the lac operon produces large amounts of mRNA coding for the enzymes that the cell needs for use of lactose
when RNA cannot bind
lactose absent, repressor active, operon off
the lac repressor is innately active, and in the absence of lactose it switches off the operon by binding to the operator. the enzymes for using lactose are not made
lactose present, repressor inactive, operon on
allolactose, an isomer of lactose, binds to the repressor, inactivating it and depressing the operon. the inactive repressor cannot bind to the operator, and so the genes of the lac operon are transcribed, and the enzymes for using lactose are made
high glucose, lactose available
when glucose is present, cAMP is scarce, and CPR is unable to stimulate trancription at a significant rate, even though no repressor is bound
Lac I
located outside the lac operon. codes for an allosteric repressor protein that can switch off the lac operon by binding to the lac operator
structural genes
Lac Z
B-galactosidase
hydrolyzes lactose to glucose and galactose
Lac Y
Permease
the membrane protein that transports lactose into the cell
Lac A
Trans-acetylase
detoxifies other molecules entering the cell via permease
Trp Operon
always on
codes for tryptophan
requires 5 enzymes
essential amino acid
synthesis: always building something
trp R
(regulatory gene)
repressor
consists of:
promoter
RNA polymerase
operator
genes of operon
trp E
trp D
trp C
trp B
trp A
RNA binds here
when RNA cannot bind
tryptophan present, repressor active, operon off
as tryptophan accumulates, it inhibits its own production by activating the repressor protein, which binds to the operator, blocking transcription. enzymes for tryptophan synthesis are not made
when RNA can bind
tryptophan absent, repressor inactive, operon on
RNA polymerase attaches to the DNA at the operons promoter and transcribes the operon genes. enzymes for tryptophan synthesis are made
differential gene expression
the expression of different genes by cells
with the same genome
chromatin modifification
transcription
RNA processing
splicing
occurs when transcription
is still under way
addition of poly A tail
addition of 5' cap
added as soon as transcription is initiated
cap and tail added, introns removed and exons spliced together
created coding segments
what a DNA strand
consists of
distal control
elements (upstream)
enhancers, thousands of nucleotides
upstream or downstream of a gene
or even without an intron
proximal control
elements
located near the promoter
exon and introns
poly A signal
sequence
the last exon of the gene is transcribed into an RNA sequence that signals where the transcript is cleaved and the poly A tail is added
termination region
(downstream)
promoter
transcription start site
transcription factors
specific
activators- lead to increased expression
enhancer
repressor
bind to DNA sequences then go to a group of mediator proteins. these in turn bind to general transcription factors and then RNA polymerase II, thus assembling the transcription initiation complex.
general
leads to low(basal) levels of transcription
TATA box
production of a few RNA transcripts from genes that are not expressed all the time, but instead are regulated
chromatin: DNA + protein
histone: responsible for the first level of DNA packing in chromatin
different types of packaging
heterochromatin
highly compacted
no genes expressed
euchromatin
less compaction
genes expressed
histones used to form core:
H2A, H2B, H3, H4
a cluster of functionally
gene related genes can be
under coordinated control of a
single on-off "switch"
how is a "switch"
turned on or off?
on
(induced)
activator bound
to operator
off
(basal)
repressor bound
to operator
oncogenes
cancer causing genes
proto oncogenes
normal cellular genes that
code for proteins that stimulate
normal cell growth and division
if mutated, can turn
into cancer cells
encode components of growth factor signal transduction pathways
tumor supressor genes
encode proteins that inhibit
abnormal cell division
p53
protein it encodes is a specific transcription factor that promotes the synthesis of cell cycle- inhibiting proteins
defective or missing transcription factor, such as p53, cannot activate transcription
BRCA2
Ras gene
G protein that relays a signal from a growth factor receptor on the plasma membrane to a cascade of protein kinases
issues signal on its own
cancer cells
exhibit neither:
density dependent inhibition
anchorage dependence
do not respond normally to the body's control mechanisms
do not need growth factors to grow and divide
make their own growth factor
may convey a growth factor's signal without the presence of the growth factor
may have an abnormal cell cycle control system
G1 phase
cell growth, accumulates materials
for DNA synthesis
S phase
DNA synthesis occurs, and
DNA replication results in duplicated
chromosomes
chromosome: consists of
one chromotid
2 chromatid= 1 chromosome
duplicated to make one chromosome
called sister chromatids
one of the multiple chromosomes in a eukaryotic cell is represented here, not yet duplicated. normally it would be a long, thin chromatin fiber containing one DNA molecule and associated proteins
once duplicated, a chromosome consists of two sister chromatids connected along their entire lengths by sister chromatid cohesion. each chromatid contains a copy of the DNA molecule
molecular and mechanical processes seperate the sister chromatids into two chromosomes and distribute them to two daughter cells
G2 phase
cell synthesizes proteins needed
for cell division
centrosome: microtubule organizing center
centrioles: pair present with in centrosome
a nuclear envelope encloses the nucleus
the nuleus contains one or more nucleoli
two centrosomes have formed by the duplication of a single centrosome. centrosomes are regions in animal cells that organize the microtubules of the spindle. each centrosome contains two centrioles
chromosomes, duplicated during S phase, cannot be seen individually because they have not been condensed
also called M phase
consisting of:
mitosis
division of cell material
cytokinesis
division of cytoplasm
prophase
chromatin fibers become more tightly coiled, condensing into discrete chromosomes observable with a light microscope
nucleoli disappear
each duplicated chromosome appears as two identical sister chromatids joined at their centromeres and, in some species, all along their arms by cohesins (sister chromatid cohesion)
mitotic spindle begins to form. it is composed of the centrosomes and the microtubules that extend from them. the radial arrays of shorter michrotubles that extend from the centrosomes are called asters
centrosomes move away from each other, propelled partly by the lenthening microtubules between them
prometaphase
nuclear envelope fragments
microtubules extending from each chromosome can now invade the nuclear area
chromosomes have now become even more condensed
kitetochore, speacialized protein structure, has now formed at the centromere of each chromatid
two sister chromatids oriented- opposite poles (stable arrangement)
metaphase
the centrosomes are now at opposite poles of the cell
the chromosomes have all arrived at the metaphase plate, a plane that is equidistant between the spindles two poles. the chromosomes' centromeres lie at the methaphase plate
for each chromosome, the kinetochores of the sister chromatids are attached to kinetochore microtubules coming from opposite poles
anaphase
begins when the cohesin proteins are cleaved. this allows the two sister chromatids of each pair to part suddenly. each chromatid thus becomes an independent chromosome
the two new daughter chromosomes begin moving toward their opposite ends of the cell as their kinetochore microtubules shorten. because these microtubules are attached at the centromere region, the centromeres are pulled ahead of the arms.
the cell elongates as the nonkinetochore microtubules lenghten
by the end of anaphase, the two ends of the cell have equivalent- and complete- collections of chromosomes
telophase
two daughter nuclei form in the cell. nuclear envelopes arise from the fragments of the parents cells nuclear envelope and other portions of the endomembrane system
nucleoli reappear
the chromosomes become less condensed
any remaining spindle
microtubules are
depolymerized
mitosis, the division of one nucleus into two genetically identical nuclei, is now complete
cytokinesis
the division of the cytoplasm is usually well under way by late telophase, so the two daughter cells appear shortly at the end of mitosis
in animal cells, cytokinesis involves the formation of a cleavage furrow, which pinches the cell in two
in plant cells, the cell plate forms dividing the two cells
2 daughter cells total
arrangement of chromosomes in pairs starting with the longest chromosome
somatic cells
all body cells except the reproductive cells
mitotically dividing and G0-arrested cells
make up vast majority of individuals tissues
diploid in nature(2N)
has two sets of chromosomes
in humans, its 46
germ cells
pockets of specialized cells
produce games (egg/sperm)
incorporated into ovaries and testis
undergo meiosis
haploid gametes
single set of chromosomes
in humans, its 23
reproductive/sex cells
sex chromosome is X
in a sperm cell, the sex
chromosome may be either
X or Y
genetic information
homologous chromosomes: two chromosomes with genes for the same traits one from each parent
Monosaccharide
simplest carbohydrate, simple sugars, these are monomers from which more complex carbohydrates are built. glucose C6H12O6
Gycosidic Linkage
a covalent bond between two monosaccharides by dehydration reaction
Disaccharide
are double sugars consisting of two monosaccharides joined by a covalent bond. they consist of two monosaccharides joined by a glycosidic linkage.
Polysaccharide
are macromolecules polymers with a few hundred to a few thounsand monosaccharides joined by glycosidic linkage. serve as storage /structure
highly nonpolar,hydrophobic, soluable in organic solvent
Ester Linkage
Bonds created when fats form
Fats
Saturated
Unsaturated
Functional molecules consisting of one or more polypeptides
polypeptides
Amino Acid
molecules with carboxyl and amino groups
Denaturation
Loss of proteins native structure; usually irreversible
Amino Acid sequence of polypeptides programed into a unit of inheritence
Nucleotide
monomer of nucleic acids
Formed by 5 carbon sugar covalently bonded to nitrogenous base and phosphate group
a reaction in which two molecules are covalently bonded to each other with the loss of a water molecule. removes water forms new bond
Polymers are broken down to monomers through this process, through adding water and breaking bond
homologous chromosomes
seperate
haploid cells with
duplicated chromosomes
prophase I
metaphase I
anaphase I
Telophase I
Cytokinesis I
pair of duplicated homologs held together by chiasma and sister chromatid cohesion
synapsis and crossing over
alignment of homologous pairs at the metaphase plate
seperation of homologs
sister chromatids
seperate
haploid cells with
unduplicated chromosomes
prophase II
metaphase II
anaphase II
telophase II
Cytokinesis II
chiasmata occurs
pair of duplicated homologous chromosomes
sister chromatids
diploid cell with
duplicated chromosomes
Process RNA to synthesize proteins
Free
suspended in cytosol and synthesize proteins that function within the cytosol
Bound
attached to outside of the ER or nuclear envelope synthesize proteins that are either included in membranes or exported from cell
Membrane enclosed; control center of cell; directs protein synthesis by synthesizing mRNA
DNA or genetic code
Membrane
Non membrane bound nucleoid
70S ribosomes
Cell Wall
Flagella
Presence of peptidoglycan
Membrane bound nucleus
80S ribosomes
Cell Wall in plants only
Flagella and cillia
protects the cell, maintains shape and prevents excessive uptake of water
Tight
membranes of adjacent cells are fused, forming continuous belts around cells. Prevents leakage of extracellular fluid
Desmosomes
Fastens cells together and anchors to the cytoplasm
Gap
They directly connect the cytoplasm of two cells, which allows various molecules, ions and electrical impulses to directly pass through a regulated gate between cells.
channels between adjacent cells that perforate plant cell walls
Has no ribosomes and is not involved in protein synthesis. Contains enzymes that synthesize the lipid membranes
Proteins that include ones that'll be released or secreted from the cell, such as proteins made into lysosomes, and also released from other locatons with in the cell,
sites of cellular respiration, generating ATP from catabolizing sugars, fats, and other fuels in the presence of oxygen
contain the green pigment chlorophyll and enzymes/molecules that function in the phosphosynthetic production of sugar
membrane-bound sac of hydrolytic enzymes that an animal uses to digest macromolecules
To produce ATP
When there is a transfer of one or more electrons from one reactant to another.
oxidation is loss, reduction is gain
Glucose (C6H12O6) is getting oxidized and Oxygen is getting reduced
the breakdown of glucose by enzymes, releasing energy and pyruvic acid.
Starts with
1 Glucose, 2 NAD+, and uses 2 ATP
Energy Investment phase
Input: glucose, 2 ATP
Output: pyruvate, 2 net ATP, 2 NADH
electron carrier involved in glycolysis
Oxidized and reduced form
oxidized
FAD
reduced
FADH2
Substrate-level phosphorylation
When an enzyme transfers a phosphate group from a substrate molecule.
Oxidative phsophorylation
The production of ATP using energy derived from the redox reactions of an electron transport chain; the third major stage of cellular respiration.
powerhouse of the cell, converts food into energy
Mitochondrial part where the ETC pumps protons
Innermost compartment of the mitochondrion
The process by which cells break down simple food molecules to release the energy they contain.
pyruvate gets reduced; hydrogen from NADH goes into pyruvate goes to forms Lactate. HADH gets recycled, glycolysis continued
causes soreness after physical exertion
the anaerobic process by which yeasts and other microorganisms break down sugars to form carbon dioxide and ethanol