chapter seventeen part two Flashcards
where does translation occur
ribosomes in the cytoplasm
how is mRNA read during translation?
5’ to 3’
how are amino acids synthesized during translation? (direction)
N to C
(amino to carboxyl group)
where is the amino acid attached on tRNA
3’ end
how many total codons are there?
64
- 61 code for 20 amino acids
codon
sequence of 3 nucleotides
- complementary to template strand
universal (almost) codes
start - AUG
stop - UAA, UGA, UAG
aminoacyl-tRNA synthetases
match tRNA and amino acid
- charge tRNA
4 steps of translation
- charging
- initiation
- elongation
- termination
- charging
- tRNA joined to respective amino acid
- tRNA has anticodon that matches the codon on mRNA
- initiation
- ribose assembles and reads mRNA 5’ to 3’
- ribosome reads AUG (start)
- tRNA w/ met into P site
- anticodon on tRNA matches mRNA codon
- elongation
- next codon read
- tRNA w/ AA into A site
- met cut from its tRNA and attached to AA in A site (peptide bond forms)
- uncharged tRNA released from ribosome to get recharged w/ met
- next codon read
- termination
- ribosome reads stop codon
- releasing factor causes addition of water molecule instead of AA to chain, breaks bond between completed polyps and tRNA in P site
co-transcriptional translation
transcription and translation occur at same time
- prokaryotes: lack of compartmental organization
polyribosomes
strings of ribosomes working on 1 strand of mRNA
- prok or euk
mutations
change in genetic material of cell
- ultimate source of new genes
base pair substitutions
- silent
- missense
- nonsense
silent base pair substitution
no phenotypic change, partly due to 2 different codons translating into same amino acid
missense base pair substitution
change 1 AA in sequence
- little effect on protein but dramatic phenotypic effect
- sickle cell
nonsense base pair substitution
change 1 AA to stop codon
- translation terminated prematurely, shorter polypeptide
insertion or deletion
addition or losses of nucleotides
- results in frameshift
frameshift
alters reading frame and triplet grouping of nucleotides on mRNA strand
- when insertion/deletion not a multiple of 3
missense downstream
wrong AA
early nonsense
stop at wrong spot
base insertion/deletion in multiple of 3
no frameshift, but AA added or missing
causes of mutations
- unknown/spontaneous
- mutagen
mutagen
physical/chemical agents that cause mutations
- radiation (ultraviolet)
- chemical (incorrectly paired nucleotides)
- virus
gene editing with CRIPSR
- altering genes in specific, predictable way
- Cas9
Cas9
nuclease that cuts double-stranded DNA molecules
- helps defend bacteria against viruses
- works with guide RNA made from CRIPSR region of bacterial genome
- cuts both strands of DNA complementary to guide RNA to trigger DNA repair system
what does guide RNA do?
guides Cas9 protein to target gene
positive potential of CRIPSR
repair gene that has harmful mutation, possible cure for genetic diseases
negative potential of CRIPSR
misapplication and ethics
peptide transferase
cuts covalent bond of AA and tRNA in P site
- attaches carboxyl end to amino end of AA attached to tRNA in A site
ribozyme
peptides transferase + RNA
DNA poly in prokaryotes
I - R&R
II - repair processes
III - most replication
DNA poly in eukaryotes
alpha and delta
RNA poly in prokaryotes
core enzyme
holo enzyme (core + sigma factor)
- sigma factor has dif types that aid in promoter selection
RNA poly in eukaryotes
I - rRNA
II - protein genes (hnRNA to mRNA)
III - tRNA, some other small RNAs
polyadenylation signal in transcription
first recognized by endonuclease
- cuts 12 nuts downstream
- poly-A polymerase adds 150-200 As
