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What is the one gene-one enzyme hypothesis?
Each gene controls production of a single enzyme.
What evidence in Beadle and Tatum’s experiment supported the one gene-one enzyme hypothesis?
They isolated mutant strains of N. crassa after X-ray- the mutant strains were blocked at a particular step in the biosynthesis pathway.
What are the major steps of protein synthesis?
Transcription (DNA becomes mRNA), RNA processing (splicing, 5’ capping, polydenylation), Translation (mRNA becomes protein), Post translational modifications (folding, phosphorylation)
What is the role of the ribosome in protein synthesis?
Initiate translation
How do ribosomes intimate translation in eukaryotes?
The small subunit binds to the 5’ end cap of mRNA with help from initiiation factors
How do ribosomes start translation in prokaryotes?
They bind the small subunits to the Shine-Dalgarno sequence of the mRNA
What do the small subunits of ribosomes do?
bind to mRNA and help align tRNA during translation
What do the large subunits of a ribosome do?
Catalyze the formation of peptide bonds between amino acids
The E-site of a ribosome
where tRNA leaves after donating their amino acid (EXIT)
The P site of a ribosome
holds the growing polypeptide chain (PEPTIDYL)
The A site of a ribosome
Holds incoming tRNA carrying amino acids (AMINOACYL)
Ribosome size of prokaryotes
70S, 50S large subunit and 30S small subunit
Size of Eukaryotic Ribosome
80S, 60S large subunit, 40S small subunit
What is the initiator tRNA in Prokaryotic translation?
N-formylmethionine
What is the imitatior tRNA in Eukaryotic translation?
AUG, methionine
Where does the ribosome initially bind to in prokaryotes?
Shine-Dalgarno sequence
Where does the ribosome bind to initially in Eukaryotes?
5’ cap
How many release factors do prokaryotes have in translation?
3, RF1, RF2 and RF3
What is the role of RF 1, 2 and 3 in Prokaryotic translation?
RF1 and 2 recognize stop codons and RF3 stimulates their activity. Promotes ribosome disassembly
How many release factors do Eukaryotes have for translation?
2, eRF1 and eRF3
What is the function of eRF1 and eRF3 in eukaryotic translation?
Recognize stop codons and GTP binding protein that helps eRF1 release the polypeptide
Where does translation occur in prokaryotes?
Cytoplasm
Where does translation occur in eukaryotes?
Cytosol
What does it mean when translation is coupled with transcription?
the ribosomes attach to mRNAa before transcription is complete
Is eukaryotic translation coupled with transcription
nah, transcription occurs in the nucleus, and translation occurs in the cytoplasm
How many combos of nitrogenous bases are there?
64
Germline mutations
Can be passed down to future generations, occurs in reproductive cells
Somatic mutations
Usually arises during life due environmental factors, can not be passed to future generations
A transition mutation
Change from a pyrimidine to another pyrimidine or a purine to another purine
Transversion mutation
change from a purine to pyrimidine or vice versa
Silent mutations
base substitutions that do not alter the amino acid of sequence of polypeptide
Missense mutation
base substitutions that alter the amino acid sequence- can be neutral or harmful
Nonsense mutation
Base substitution that can change a normal codon to a stop codon
Frameshift mutations
add or delete nucleotides not divisible by 3. Shifts the reading frame.
What did the Lederberg experiment determine?
The mutation for antibiotic resistance is spontaneous and arise’s randomly.
A reading frame
a way to divide nucleotide sequences into triplets
An open reading frame
A specific sequence within a reading frame that has a start codon and lacks a stop codon for a while- good candidate for coding a protein.
Spontaneous mutations
result from abnormalities in the biological process
Induced mutations
Chemical or physical agent known to alter DNA structure
Causes for spontaneous mutations include…
Depuration, deamination, tatuomeric shift
Deamination
Removal of an amino group from cytosine base- if not repaired C-G or A-T mutation occurs
Point mutations
effect a single nucleotide. Can be silent, missense or nonsense.
Frameshift mutations cause ____ protein changes
major
Some examples of mutagens
nitrous acid, nitrogen mustard gas, acridine dye, 5-Bromouracil
Some examples of physical mutagens
X-rays and UV light
Histone acetylation of chromatin causes…
Nucleosomes become loose and allow transcription factors to bind to DNA
DNA methylation of chromatin causes
Tightly packed nucleosomes. Transcription factors cannot bind.
What is dosage compensation?
genetic mechanism that ensure equal expression of X-linked genes between males and females.
In placental mammals, how is dosage compensation achieved?
One of the two x-chromosomes in somatic cells is randomly silenced to balance gene expression with males.
Cis-acting elements
DNA seqeunces that exert their effect over a particular gene (TATA box, enhancers, silencers) (Next to)
Trans-acting elements
Regulatory factors or proteins that bind to such DNA sequences. (across from)
Enhancers
Increase gene expression by promoting RNA pol. to bond and recruiting transcription factors
Enhancers bind to
Activators and coactivators
Silencers
Decrease or suppress gene expression. Block transcription or alter chromatin structure.
Silencers bind to
Repressors and corepressors
Eukaryotic transcription requires ___ ___ in addition to RNA polymerase
transcription factors
Transcription factors bind to _____ in order to ______
the promoter region to help recruit RNA polymerase for transcription initiation
3 Regulatory factors
Activators, Repressors, Mediators
Activators
Bind to DNA and facilitate or enhance transcription
Repressors
bind to DNA and silince or inhibit transcription
Mediators
can respond to hormones, stress or signals to modulate gene expression
General factors include
TFIID, TFIIB, TFIIE, TFIIF, TFIIH
TFIID
contains tata binding protein which recognizes tata box
TFIIB, E, F and H
Assist RNA polymerase II recruitment and transcription initiation
TFIIH
Has helicase activity which unwinds DNA and Kinase activity which phosphorylates RNA polymerase II to start transcription
Kinase
phosphorylates RNA polymerase II to start transcription
Common ways gene expression is regulated in transcription
Binding of small effector molecule, protein-protein interactions, covalent modifications
Allosteric interactions
binding to a non-active site on a protein, results in conformation and activity change.
Protein protein binding can cause ___
allosteric interactions
Covalent modifications
can activate or inhibit transcription factors via allosteric interactions EX. Phosphorylation
Effect of small effector molecule in transcription control
Regulates gene expression by modulating transcription factor activity. Activate or inhibits transcription factors, altering gene expression in response to environmental or cellular conditions.
A mutation on the promoter would likely…
weaken or eliminate RNA pol. binding. Causing lower transcription or complete loss of gene expression.
A mutation on the enhancer would likely ….
Prevent activators from binding. Transcription would be lowered and gene expression would be reduced
A mutation on the silencer would likely …
Prevent the repressor from binding, uncontrolled gene expression would increase.
siRNAs
Perfectly complementary to mRNA, degrades mRNA, exogenous
MicroRNA, miRNA
encoded in DNA (endogenous), primarily found on 3’ UTR, stored in processing body in cytoplasm.
Why is RNA processing considered a form of post transcriptional regulation?
If RNA is not spliced it can’t exit the nucleus for translation. If it cannot be translated it cannot be expressed.
What is the implication of phosphorylation on protein activity?
Could change how the protein works (Chromosome accessibility transcription factor binding, stability etc.)
Why in a multicellular organism, different cell types produce different gene products even though they contain the same genetic material?
because of a process called gene regulation, where each cell type selectively "turns on" or "turns off" specific genes based on signals from its environment, allowing it to express only the genes necessary for its specialized function, leading to distinct protein profiles for each cell type