Chapter 7- RNA and the Genetic Code Flashcards Preview

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Flashcards in Chapter 7- RNA and the Genetic Code Deck (38)
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1

monocistronic

eukaryotic mRNA is monocistronic, meaning that each mRNA molecule translates into only one protein product.

2

polycistronic

prokaryotic mRNA may be polycistronic, and starting translation at different locations in the mRNA can result in different proteins

3

aminoacyl-tRNA synthetase

different types activate different amino acids, requires 2 ATP

4

start codon

AUG (codes for methionine)

5

stop codon

UAA (U Are Annoying)
UGA (U Go Away)
UAG (U Are Gone)

6

only amino acids with one code

methionine and tryptophan

7

wobble position

third position for codon. usually the first two nucleotides are the same so the third is a variable one. mutations here are typically silent or degenerate mutations.

8

expressed mutations

1. missense: one amino acid substitution
2. nonsense: mutation encodes for a premature stop codon (aka. truncation mutation)

9

TATA Box

promoter region for RNA polymerase II to bind during transcription. typically in -25 for gene location numbering system.

10

2 differences between DNA and RNA polymerases

RNA polymerases don't require an RNA primer to start generating a transcript and they dont check their work, no editing done.

11

heterogeneous nuclear RNA (hnRNA)

primary transcript and after some modifications it becomes mRNA

12

steps between hmRNA and mRNA? (known as posttranscriptional processing)

1. Intron/exon splicing
2. 5' cap
3. 3' poly-A tail

13

intron/exon splicing

spliceosome: made up of small nuclear RNA (snRNA) and small nuclear ribonucleoproteins (snRNPs). these recognize introns and cuts them out to form a lariat (lasso-shaped structure). they are then degraded.
introns- noncoding sequences are removed
exons- coding sequences are ligated

14

alternative splicing

primary transcript of hnRNA may be spliced together in different ways to produce multiple variants of proteins encoded by the same original gene. many more proteins made from limited genes

15

RNA Polymerase I

Synthesizes rRNA

16

RNA Polymerase II

Synthesizes mRNA (and hnRNA)

17

RNA Polymerase III

Synthesizes tRNA and some rRNA

18

3 steps in translation

1. initiation
2. elongation (APE sites)
3. termination

*Note: all steps require energy

19

what happens at the P site for translation (during elongation)

peptide bond forms using peptidyl transferase (enzyme part of the large subunit). GTP used for energy.

20

chaperones

assist in protein folding

21

carboxylation

usually serves as a Ca2+ binding site

22

phosphorylation

usually activates or deactivates a protein

23

operon

cluster of genes transcribed as a single mRNA. 2 types: inducible and repressible systems. offer a simple on-off switch for gene control in prokaryotes.

24

Jacob-Monod Model of an operon

1. regulator gene- codes for repressor protein
2. promoter site- RNA polymerase binding site
3. operator site- nontranscribable and can bind a repressor protein
4. structural gene- codes for protein

25

inducible system (prokaryotes)

repressor bound tightly to operator system so RNA polymerase cannot get to structural gene. inducer must remove the repressor. positive control mechanism b/c repressor is removed from operon by the inducer to promote transcription.

26

1 example of an inducible system (prokaryotes)

lac operon only induced in presence of high lactose and low glucose. assisted by binding of catabolite activator protein (CAP)-starts transcription.

27

negative control mechanism (prokaryotes)

repressible systems. repressor-corepressor complex binds to the operon to prevent transcription.

28

repressible systems (prokaryotes)

allow constant production of a protein. repressor is made by regulator gene in inactive until it binds to a corepressor. then this complex binds to the operator site preventing further transcription. negative control mechanism b/c typically protein being made is the corepressor.

29

1 example of a repressible system (prokaryotes)

trp operon controls manufacturing of tryptophan. when tryptophan is high in local environment it acts as a corepressor.

30

transcription factors

transcription-activating proteins that search DNA for specific DNA-binding motifs. 2 recognizable domains: DNA-binding domain and activation domain.