Test 3-dna replication, protein synthesis, gene mutations Flashcards
Whatre the four enzymes in dna replication, what do they do
Helicase unzips (breaks h bonds between bases)
Rna primase lays down a primer (origin of replication, dna polymerase cannot replicate without it), dna polymerase positions and joins compliemtary bases with h bonds, replaces rna primer with dna primer, proofreads codes, checking for errors, ligase joins sugar phosphate together by dehydration synthesis and okazaki fragments
Are primers removed in dna replication
Yes, replaced with dna nucleotides (Doesnt become dna primer)
What way does dna polymerase read and add nucleotides
Read: 3’ to 5’
Add: 5’ to 3’
Which starting strand is the leading and lagging strand (with respect to the direction helicase is unzipping in)
Leading: 3’ to 5’
Lagging: 5’ to 3’
Which form faster: the hydrogen bonds or covalent bonds in dna, why
Hydrogen bonds, formed by dna polymerase, while covalent ones are formed after with ligase
Whats a gene, what is gene expression also called and why
A segment of dna found on the chromosome that specifies the amino acid sequence of a polypeptide
Also called gene expression, since transcribing the gene means its activated/ expressed (proteins are being made from that gene)
Does rna polymerase need a primer, why
No, because it attaches to the promoter site and begins to unwind/unzip dna
Which strand is the template strand for rna polymerase
3’ to 5’, leading
What is around the gene being transcribed
Promoter and termination site
Whatre the three post transcriptional modifications of pre mrna
Capping: adds cap (modified guanine) on 5’ end
Tail: poly a tail (Adenine) added to 3’ end
Splicing: spliceosomes take/splice out introns
What does the cap and poly a tail do, where are they found on the mrna
Cap: 5’, turns the 5’ end into the leading end and prevents degradation
Tail: 3’: prevents damage/degradation
Whatre introns, what happens to them in splicing
Noncoding regions of mrna, get spliced out
Whatre the three steps of translation, give a brief definition
Initiation: small ribosomal subunit binds to mrna at start codon aug, large subunit and anticodon arrives
Elongation: trna brings the next amino acid to a site, peptide bonds between the amino acids form, elongation continues until the ribosome reaches a stop codon
Termination: stop codon reached, release factor (which doesnt contain amino acid) enters a site, trna released and polypeptide chain released from trna while ribosome dissociates
Whats a polyribosome
When there are multiple ribosomes reading one strand
Whatre the three sites of ribosome and what do they do
A: accepting/amino acid site: where trnas with amino acids enter from
P: peptide/ peptidal site: trna releases amino acid (polypeptide chain grows here)
E: exit site, exit for trna after amino acid is released
Where does aug codon start at, where does the polypeptide chain grow from
Starts at p site
Grows from p site
When do large and small subunits separate
To release mrna
Whats another name for the ribosome
Initiation complex
What does the stop codon do
Doesnt code for amino acid, but is recognized by the release factor, a protein that stops translation
Whats a mutation
A permanent change in the sequence of bases that make up a particular gene
What can cause mutations
Errors in replication (rare), mutations/carcinogens (ex. Radioactivity, x rays, uv radiations), organic chemicals in cigarettes (tar), pesticides, and environmental factors, transposons
Whatre transposons
Specific dna sequences that can “jump” within and between chromosomes, disrupting gene expression (Ex. Causes frameshift mutation)
Whatre the two types of mutations (just names are okay)
Point mutation
Frameshift mutation
Whats a point mutation, what does it change, whatre the three point mutations
When one nucleotide in a gene sequence is accidentally paired with the wrong nucleotide during replication or transcription
Changes one nucleotide (one amino acid)
Silent mutation: no effect, code changed results in same amino acid
Missense: one amino acid is changed, possibly results in alteration/ loss of protein function
Nonsense: stop codon (or start) changes, protein function is completely lost
