transcription, translation, mutation Flashcards
protein synthesis
How cells follow DNA directions on how to make proteins
Each chain of nucleotides is a
line of code
Each chain of nucleotides contains
directions for making many different proteins
each set of directions is a gene
one gene= one protein= one trait
steps in making a protein
1) Copy the Directions for one protein onto RNA (one gene)
Transcription
2) Use the RNA directions to make a protein
Translation
Transcription
Copy the Directions for one protein onto RNA (one gene)
RNA polymerase scans the DNA to find the gene it needs to copy
mRNA carries coded directions out into cell where it binds to a ribosome
what four jobs does RNA polymerase do in in transcription
1) unwind the DNA double helix
2) breaks hydrogen bonds to separate chains
3) match RNA nucleotides to the DNA gene
4) fuse the RNA nucleotides together to make a chain of RNA
mRNA
The chain of RNA that is made is called mRNA
Or messenger RNA
Translation
Translates nucleotide code of RNA into
the amino acid code of a protein
translation takes place where and is done by what
Takes place in the cytoplasm
Is done by a ribosome
mRNA
chain of nuclotides that make up the coded directions for making the protein
codon
the code for one amino acid
Every 3 nuclotides of mRNA is a codon
ribosome structure
made of two subunits; large ribosomal subunit made of RNA and small ribosomal site made of proteins
how does process in ribosome start
Subunits bind onto mRNA chain at start codon (P)
how many codons at a time are in ribosome
3
which codons are being read
codons in P and A
what do the letters E P and A stand for sites
E exit
A add on
P where it starts
what does tRNA do
bring amino acids to the ribosome Match the correct amino acid in place by matching their anti-codon to the mRNA codon Fit into the E, P and A sites
how many amino acid types do each tRNA pick up
ONLY ONE KIND
what does tRNA do after dropping off amino acids at ribosome
moves back into the cytoplasm to pick up another amino acid(but always the same kind)
what enzyme binds amino acids to tRNA
aminoacyl-tRNA synthetase
steps to translation
initiation
elongation
termination
translation initiation
Ribosome subunits bond to mRNA
tRNA that matches start codon binds at site P
translation elongation
tRNA that matches 2nd codon binds at site A
ribosome attaches the 2 amino acids those tRNAs carry to each other by a peptide bond
Ribosome moves down mRNA chain by one codon
the first tRNA
Moves into the E
site and exits
the ribosome
the next tRNA moves into place
translation termination
Ribosome moves down mRNA to stop codon
Release factors bind to stop codon instead of a tRNA
Ribosome, mRNA, tRNAs and protein all break apart
what is the wobble effect
There are 60 possible codons but only 45 tRNAs so only 45 anti-codons
Some tRNAs can bind to more than one codon
The last base in the anti-codon has some flexibility in what it binds to (wobble room)
mutations caused by
spontaneous errors
mutagens: chemicals/radiation
mutations can happen in
body cells (somatic cells) or In reproductive cells (egg & sperm)
Somatic cell mutations (may cause)
May cause no change = if mutated gene is one that is not use by that particular cell
May cause cell to die
May cause cancer
Not passed on to children
Reproductive Cell or Early Embryo Cell Mutations
Child with mutation Every cell of the child is mutated May cause miscarriage May cause a genetic disorder in child May have no effect at all
Gene mutation
DNA coding error
may be a missense mutation where the codons code for the wrong aa ….
or nonsense where stop codon or partial codon
chromosome mutation
change in chromosome number, missing or extra chromosome pieces
gene mutations: point mutations (substitutions)
change only one base pair
a) substitution of 1 nucleotide for another b) ATT becomes ATG..(missense) c) may not cause any change = silent mutation d) may change 1 amino acid e) could be nonsense only if codes for stop e) can cause disorder
gene mutations : framshift mutations
change all the codons
a) insertion b) deletion c) THE FAT CAT = HEF ATC AT d) most always ruins protein
gene muations: tandem repeats
codons repeated over & over
most often ruins protein
more repeats = more problems
transcript
chain of RNA as copied from DNA template
Pre-mRNA
a transcript that will become mRNA
Transcripts become
mRNA tRNA or rRNA
Transcripting process
Cap, poly A tail, RNA splicing
transcripting process Cap
Pre-mRNA transcript has a cap added to 5’ end
cap facilitates exit through nuclear pore
cap aids in translation initiation
cap is attached to a UTR (untranslated region)
UTR is followed by the start codon
Transcripting process poly A tail
3’ end of transcript gets a poly-A tail added to it
A bunch of A ribonucleotides added on
More As added make
the mRNA last longer
Fewer As added make
the mRNA break down quicker
in transcripting process break down
Breakdown starts immediately on entry to cytosol
Hydrolytic enzymes
starts from tail end
RNAQ splicing parts
introns and exons
Introns are cut out, exons fused together
introns
in between coding regions of RNA
do not code for a.a.s
are cut out before mRNA leaves nucleus
bacteria do NOT have introns
exons
have codons that are executed by translation….code for a.a.s\
Alternative splicing
used to make multiple proteins from one gene
Exons are spliced together in different orders
spliceosome
Complex of proteins and small RNAs
Remove introns
Joins exons in proper order
RNAs in spliceosome are Ribozymes…RNA enzymes
Sometimes the intron being removed IS the ribozyme
Evidence for RNA before DNA
RNA can act as its own enzyme
RNA polymerase can initiate polymerization on its own
DNA polymerase can only start polymerization at a primer
That is created by RNA polymerase
all translation begins in
cytoplasm
The first few aa at leading end of those proteins =
a signal peptide
process of protein being transported to rough er
Signal peptide binds to a Signal Recognition Particle (SRP)
SRP escorts ribosome to receptor protein on ER
Protein synthesis completed on the ER and growing polypeptide chain is fed into the ER for folding & processing
Proteins that enter ER are made for
destined for endomembrane system or produced for secretion (insulin)
what happens to proteins that are completed in the cytoplasm
stay in cytoplasm
Post-translational modification
Completed protein is modified
Amino acid modification – add functional groups
Trim aa from cap end
Cleave polypeptide into pieces
Join 2 polypeptide into quaternary structure with disulfide bonds
Differences among Domains: Replication
Bacteria, Archaea, eukarya
Bacteria – No histones, 1 origin, circular DNA
Archaea – Have histones, 1 origin, circular DNA
Eukarya – Have histones, Many origins, Linear DNA
Differences among Domains: Transcription Bacteria
NO transcription factors needed for RNA polymerase to recognize promoter
one type of RNA –polymerase
terminator ends transcription…NO transcript processing
(no splicing)
Differences among Domains: Transcription Archaea
Require transcription factors
one type of RNA -P
No conclusive evidence at this time
Differences among Domains: Transcription Eukarya
Require transcription factors
3 types of RNA polymerase
different signal ends transcription depending on the type of RNA DO transcript processing for all RNA
structure of RNA-P very similar between
Archaea and Eukarya
Differences among Domains: Translation
Bacteria and Eukarya
Bacteria- translation begins before transcription is complete
translation begins before transcription is complete
Eukarya- translation in cytoplasm after transcript processing
Ribosomes include 4 RNA molecules
