Genetics Exam 3

Scary stuff

non-coding mutation

does not occur in a protein coding region → may or may not be expressed or have phenotypic effects

coding mutation

occurs in a protein coding region

missense

changes one amino acid to another in the DNA sequence

nonsense

changes one amino acid to STOP (truncates protein)

loss of function allele

has a lesser function in relation to the wild type allele, and a new allele is generated

Can…

• reduce transcription

• reduce translation

• reduce protein activity

Most mutations are LOF because it is easier to break a gene with a random change than to make it work/develop a new function

Amorphic (null)

deleted, no function (LOF)

HYPOmorphic

reduced function (LOF)

gain of function

MORE of the same function is present

Can…

• increase transcription (perhaps in cells that dont usually express this gene)

• increase translation

• increase protein activity / cause a new kind of activity

HYPERmorphic

more of the usual function (GOF)

NEOmorphic

new function / epotic (in a new place) expression (GOF)

ANTImorphic

new function, a new protein product whos goal is to sabatoge the WT alleles (might bind where they would) (GOF)

haplosufficient

presence of 1 WT allele is enough for the WT phenotype to be expressed (most mutations are haplosufficient

happloinsufficient

presence of 1 WT allele is NOT enough for the WT phenotype to be expressed

incomplete dominance

occurs when a phenotype is sensitive to the levels of function and therefore the phenotype is sensitive to expression level

inducible

default state is OFF but can be turned ON (transcription)

repressible

default state is ON but can be turned OFF (transcription)

constitutive

ALWAYS on → regardless of induced/repressed

permease

lacY

membrane protein that allows lactose to easily enter the cell

without it, very little lactose can enter the cell

B-galalactose

lacZ

enzyme that cleaves lactose into glucose and galalactose

operon

multiple genes (2 or more) that get transcribed into a single mRNA that encodes multiple proteins (polycistronic mRNA)

cis (acts as binding site)

only present in prokaryotes (NOT EUKARYOTES) because they have specific regulators for expression

lac repressor protein

trans (wants to bind to the operator)

lac operon

inducible system

default state is OFF

adding stimulant (lactose) induces operon to turn ON, lactose induces the operon by removing negative regulation (stopping the repressor from binding)

lacI-

this protein encodes for the repressor (not apart of the lac operon) **has its own promoter

lacI^S

super repressor that prevents the repressor from binding allolactose, so that it is always in the DNA-binding conformation

lacP^-

change in sequence of lac promoter preventing RNAP from binding

lacO^C

c = constitutive

change in sequence of lac operator so repressor cannot bind (exhibits constant expression)

acts in cis because it causes constitutive expression of ONLY the alleles on the same chromosome

euchromatin

loosely packed chromatin and is accessible

heterochromatin

condense, tightly packed chromatin and is inaccessible

histone modifications

acetylation increases the accessibility of DNA (most common way to increase accessibility)

DNA methylation

adding a methyl group to specific DNA sequences actually modifies the DNA itself

usually cytosine in eukaryotes

almost always associated with heterochromatin formation and gene silencing (histone does not do this)

toooo much methylation of something that is not usually methylated can cause the sites to silence the genome

Nucleosomes (histone + DNA) sliding/reorganization

repressors/co-activators evict/slide histone proteins to make a protein more or less accessible (can impact other regions)

upstream

3’ end of the template strand

5’ end of RNA

downstream

5’ end of the template

3’ end of RNA

RNAP builds towards the 5’ end of the template as it builds from its own 5’ → 3’

CIS elements

apart of the DNA strand (same molecule) and regulatory elements

regions of DNA that are required for gene expression/regulation

TRANS elements

NOT apart of the DNA sequence that they are regulating

they are diffusible molecules that bind cis elements (float around and find their binding sites)

promoters

ALWAYS upstream from the transcribed portion of a gene

location must be in correct direction and is crucial for RNAP to bind in the correct spart to start

enhancers

cis to the genes they regulate

their location is not as particularly important as a promoter

the closer they are to the gene they regulate, the more recognizable it is

basal factors

are TFs that bind to promoters and recruit RNAP

binding results in little (to 0) transcription levels

set the ‘baseline’ expression level

activators/repressors

TFs that bind to the enhancer (don’t actually bind to the promoter)

activator binds → transcription increased

repressor binds → transcription decreases

initiation phase (translation)

complex of ribosome, first charged tRNA, mRNA

in prokaryotes: can happen while mRNA is still being transcribed

in eukaryotes: CANNOT happen at same time, transcription happens in the nucleus & translation happens in cytoplasm/ER after it is exported out of the nucleus

shine-dalgarno sequence

(initiation) in prokaryotes

positions ribosomes by start codon

the SDS and the start codon tell the ribosome where to bind

5’ cap

(initiation) in eukaryotes

directs the ribosome to the 5’ UTR of a eukaryotic mRNA (the start is usually the first AUG)

elongation phase

peptide bonds form as charged tRNAs bringing the appropriate AA to the ribosome

(building a peptide)

A site (aminoacyl) - new tRNA carrying an AA enters

P site (peptidyl) - holds the growing peptide chain (comes from A site)

E site (exit) - the empty tRNA (no longer holding the AA) leaves

termination phase

stop codons signal release factors and the complex disassociates

there is NO stop tRNA

occurs when stop codon is reached & a release factor binds

peptide bond

formed when the ribosome catalyzes the dehydration synthesis between two AA

results in a N-terminus and C-terminus → means there is polarity (2 distinct ends)

aminoacyl-tRNA

brings together the amino acid and the tRNA → synthesizes a ‘‘charge’’