Chapter 17 - Gene Expression Flashcards
is RNA usually double or single stranded
single
what is transcription?
the synthesis of RNA using information from DNA
what is mRNA?
for a protein coding gene, the resulting complementary RNA strand is a transcript of the gene’s protein building instructions and is called mRNA because it carries a genetic message form DNA to ribosomes
what is translation?
the synthesis of a polypeptide using information in the mRNA
RNA is translated into amino acid sequence of a polypeptide
what is coupling? where does it occur?
bacteria don’t have nuclei so their DNA isn’t separated by nuclear membranes from ribosomes –> coupling means that ribosomes can attach to the 5’ end of a mRNA molecule while it is being made by transcription from the DNA template
in eukaryotic cell, the nuclear envelope separates transcription and translation
what is RNA?
a sequence of ribonucleotides complementary to a DNA template
What are the stop codons?
UAA, UGA, UAG
Don’t encode amino acids
What’s the start codon for translation
AUG
Also codes for Met
Difference between RNA and DNA polymerase?
RNA polymerase doesn’t need a primer!
What’s a promoter?
A DNA sequence where RNA polymerase attaches and initiates transcription
What does RNA pol I do?
Synthesize rRNA
What does RNA pol II do?
Synthesizes mRNA
What does RNA pol III do?
Synthesizes tRNA
Set up of transcription
Promoter contains within it the start point –> RNA pol II binds to promoter only after transcription factors are attached to the promoter
The entire complex of transcription factors and RNA pol II bound to the promoter is called the transcription initiation complex
What unwinds the DNA and starts transcription?
RNA pol II
What’s the TATA box?
A nucleotide sequence within the promoter that upstream from the start point - a transcription factor has to bind to it first before RNA pol II can bind to DNA
Elongation during transcription
A single gene can be transcribed simultaneously by multiple polymerase molecules, like a convoy –> increases amount of mRNA transcribed so cell can encode protein in large amounts
Prokaryote vs eukaryotes termination of transcription
Bacteria: DNA goes through transcribed terminator sequence, detaches, and requires no further modification
Eukaryotes: RNA pol II transcribed a sequence from the DNA called the polyadenylation sequence (AAUAAA) –> 10 nucleotides downstream, certain proteins cut the DNA free from the polymerase and free the pre-mRNA –> RNA pol II continues to transcribe but new 5’ end isn’t protected by a cap so it’s degraded
What is a 5’ cap
A modified form of guanine that’s added after transcription of the first 20-40 nucleotides
What is a poly A tail?
After polyadenylation signal is transcribed and pre-mRNA is set free, enzyme then adds 50-200 more adenine (A) nucleotides
RNA splicing
RNA splicing removes large portions of RNA that are initially synthesized
The noncoding segments of nucleic acid in RNA that lie between coding regions are called introns
The other regions are called exons because they will eventually be EXpressed (translated into amino acids)
What removes introns from pre-mRNA
Removal of introns is accomplished by a large complex of proteins and small RNA called a spliceosome
What is alternative RNA splicing
A single gene can encode more than more kind of polypeptide depending on which segments are treated as exons during RNA processing!
What are the two ends of a tRNA
The 3’ end protrudes and is the attachment site for an amino acid
The other end is the anticodon which is the nucleotide triplet that base pairs to a specific mRNA codon
What correctly matches up tRNA with its appropriate amino acid
Aminoacyl-tRNA synthetases –> the active site of each synthetases fits only a specific combination of tRNA and amino acid but each synthetases can fit all the tRNA for the specific amino acid
Catalyzes covalent attachment of amino acid to tRNA in a process driven by hydrolysis of ATP
What is wobble
There isn’t a tRNA for each mRNA because there is flexible base pairing –> tRNA anticodon UCU can pair with mRNA codon AGA or AGG which both for for arginine
Difference is usually in the third codon
Where are the subunits of ribosomes made?
Nucleolus
Eukaryotic vs bacterial ribosomes
Eukaryotic are larger and different in molecular composition which is significant because certain antibiotic drugs can inactivate bacterial ribosomes without affecting eukaryotic ribosomes
rRNA in translation
It’s primarily responsible for both structure and function of the ribosome and acts as a catalyst of peptide bond formation
What energy does translation use
GTP
What are the different ends of the polypeptide chain?
The chain is synthesized in one direction from the initial Met at the amino end called the N-terminus towards the final amino acid at the carboxyl end called the C-terminus
Amino acids are added one by one at the C-terminus
Free vs bound ribosomes
Free ribosomes are suspended in the cytosol and synthesize proteins that say in the cytosol
Bound ribosomes are attached to the ER or nuclear envelope and make proteins of the engine brand system as wrk a proteins to be secreted from the cell
Ribosomes can alternate between being free or bound
What are missense mutations?
Substitutions that change one amino acid to another
Don’t always do damage because functions of the amino acids can be similar to each other
What’s a nonsense mutation
A point mutation that changes the codon for an amino acid into a stop codon and causes translation to be terminated prematurely –> resulting polypeptide will be shorter than the polypeptide encoded by the normal genes which usually leads to nonfunctional proteins
What’s a frameshift mutation?
Occurs whenever the number of nucleotides added or deleted aren’t multiples of three and the result is missense which usually ends in nonsense and premature termination
Insertion or deletion usually alter the reading frame so the triplet groups are messed up –> usually worse than substitutions
