Saved Unit 6 Protein synthesis & Gene Control

structural genes

genes that code for a protein/RNA product that isn't a regulatory factor

examples that structural genes code for

amino acid sequence, ribosomal RNA, tRNA; In a lac operon, they code for enzymes to metabolize lactose

relationship between switches, control genes, transcription factor genes/factors, structural genes

Switches are sequences of DNA that turn on/off protein-making genes. They are promoters, enhancers, terminators or silencers. Control genes are genes that throw the switches on/off. A type of control gene is a transcription factor gene, and they code for the proteins that attach to the switch to activate/deactive it. This gene is constitutive (always on) & controlled by negative feedback (ex. concentration of product increases, production of TF is decreases). A structural gene can be inducible (controlled by responsive/body plan TF) or constitutive (controlled only by general TF/feedback inhibition)

explanations of the 3 types of TF's

1) General TF attach to the "core promoter" sequences and are found on most genes. They are always in the nuleus

2) Responsive are only produced in cells that need them, turned on allosterically, turn on structural genes when needeneed them, turned on allosterically, turn on structural genes when needed

3) Body plan affect many switches and lead to specialization of cell, generate signals that develop body partsd

3) Body plan affect many switches and lead to specialization of cell, generate signals that develop body parts

genes for switch regions/production of TF have been "conserved" over time, so mutations/change in these sequences are generally ______ but when it is a _______________, this ______

selected against so don't happen; selective advantage; proliferates quickly

steps of protein synthesis for eukaryotes

1) Initiating transcription= each gene has its own promoter: multiple TF at promoter + other switch regions

*In nucleus

2) Transcription= makes mRNA

a) RNA polymerase builds pre-RNA

b) RNA maturation w/introns: 5’ cap & 3’ poly A tail added, spliceosome bends & cuts out introns

c) mature mRNA goes to the ribosome by leaving the nucleus and the DNA rezips

3) Translation= makes polypeptide

a) initiation: tRNA is charged, translation complex is formed

b) elongation: the polypeptide is formed

c) termination: release factor, translation complex unassembled

location/steps of protein synthesis for prokaryotes

*all in the cytoplasm

1) Initiating transcription= An operon is activated to allow transcription and DNA unzips

2) Transcription= makes mRNA

- mRNA strand is made from a DNA template

- mRNA goes to the ribosome and the DNA rezips

3) Translation=makes polypeptide

a) initiation: tRNA is charged, translation complex is formed

b) elongation: the polypeptide is formed

c) termination: release factor, translation complex unassembled

operator=

switch

repressor=

TF

inducible operon vs. repressible operon

Repressors are attached to the promoter region until inducer can take it off, turning on the gene; repressors are not attached to the promoter region until the inducer puts the repressor on the gene, turning the gene off

explain the Trp operon (repressible)

if there is excess tryptophan (above set point) it attaches to the repressor, which activates it, which turns OFF gene. Tryptophan is the inducer. For neg. feedback loop, lets say there is excess tryptophan (above set point). This would mean there is enough tryptophan to be an inducer. It would bind to the repressor/TF, deactivate it, block DNA polymerase, blocking transcription.

what is development

event where multiple genes r expressed at the same time. This requires orchestration of powerful TF. However, cells during this event express genes differently to produce the diff types of cells in multicellular animals

when methyl group added to bases in sequence ______. Methylation can be affected by ____ ____

region is deactivated (promoter and regulatory most often); environmental stressors

if acetyl group added to histone, ______

the DNA unwinds from tight coil

in eukaryotic cells how can multiple genes be controlled together

the 3 genes may be on diff chromosomes but would be activated by the same TF, activating all of them

why wouldn’t keratinocytes produce melanin and why

Most non‑sex cells in mammals contain the same chromosomes with the same genes (genomic equivalence). Cell differentiation occurs when different cells express genes for proteins that are specific to that cell type. So, to answer the q, it’s because keratinocytes don’t have the gene for the transcription factor that activates the transcription genes to produce melanin

when is a poly-tail added

poly‑A tail is added before translation at the ribosome

do more bands in gel display more complexity

no

pyrimidine

purine

single ringed

double ringed