Chapter 14

Question 1

anatomy of RNA transcripts

Answer 1

1. untranslated regions flank protein coding region; 3’ UTR affects the stability and translation of mRNA
2. Shine-Dalgrano sequence in bacteria is right upstream of the start codon and is where the ribosome binds to mRNA for translation
3. protein coding region is Madde up of codons that each specify an amino acid
4. introns are non-coding regions that break up coding regions (axons) in eukaryotes

Question 2

transcription and translation are ______ in eukaryotes

Answer 2

uncoupled

Question 3

where does transcription and translation happen in eukaryotes?

Answer 3

transcription happens in the nucleus, translation happens in the cytoplasm

Question 4

pre-mRNA

Answer 4

needs modification before its mature mRNA

Question 5

what are some modifications of mRNA?

Answer 5

addition of 5’ cap
addition of 3’ poly A tail
splicing out of introns
alternative processing
RNA editing

Question 6

addition of 5’ cap

Answer 6

guanine is added to the 5’ end of mRNA and is methylated
helps with mRNA stability, ribosome binding, and intron removal

Question 7

addition of 3’ poly A tail

Answer 7

50-250 adenine nucleotides on 3’ end
helps with mRNA stability, ribosome attachment, and mRNA export to cytoplasm

Question 8

splicing of introns

Answer 8

consensus sequences at exon/intron junctions and internal branch point guide splicing
spliceosome= RNA and proteins

Question 9

alternative splicing

Answer 9

different combos of exons retained and spliced together
6-exon gene and 4-exon mRNA in thyroid cells makes calcitonin protein that regulates calcium levels
same 6-exon gene and 5-exon mRNA in brain cells makes CGRP protein that helps with pain transmission and blood vessel dilation
***different splicing can lead to differentiation of cells and function

Question 10

what is alternative processing and what are the 2 ways to do it?

Answer 10

makes different proteins from the same gene
1. alternative splicing
2. multiple 3’ cleavage sites

Question 11

multiple 3’ cleavage sites

Answer 11

proteins of different lengths can be produced from one gene

Question 12

what does alternative processing effect?

Answer 12

can happen in 90% of human genes, can vary between people, and contributes organismal complexity

Question 13

RNA editing

Answer 13

guide mRNA changes sequence of mRNA message

Question 14

tRNA

Answer 14

each tRNA is specific for a different amino acid
incorporates rare modified bases
75-95 nt in length
processed after transcription

Question 15

cloverleaf tertiary structure of tRNA

Answer 15

amino acid attachment site has conserved sequence where amino acid binds
anticodon is 3 nt long and interacts with codon in mRNA
aminoacyl-tRNa synthetase enzymes pair tRNA with the correct amino acid
*acceptor stem at one end, anticodon at the other end

Question 16

rRNA

Answer 16

ribosomes are one of the most abundant molecular complexes in a cell
-made of RNA and protein
-one large and one small subunit
80% of total cellular RNA is in the ribosomes

Question 17

rRNA genes

Answer 17

copy number varies across species
one long transcript may be methylated and cleaved to produce different functional rRNA molecules
small nucleolar RNAs and protein cleave and modify rRNAs and assemble them into mature ribosomes in eukaryotes

Question 18

RNA interference

Answer 18

small interference RNAs (siRNAs) and microRNAa (miRNAs)
negatively regulate target genes via
1. degradation of mRNA
2. inhibition of transcripts (siRNA) or translation (miRNA)
3. chromatin modification
4. siRNA targets gene from which it was transcribed; miRNA targets other genes and thus has limited complementarity to them

Question 19

mechanism of RNA interference

Answer 19

1. double stranded RNA is cut by Dicer
2. small piece of RNA joins with protein to form RNA-induced silencing complex
3. RISC pairs with target mRNA and cleaves it (siRNA) or inhibits translation (miRNA)

Question 20

what are other small RNAs?

Answer 20

piwi-interacting RNA- suppresses transponsons
CRISPR-bacterial defense and biotechnology
snRNAs and snoRNAS- post-transcriptional RNA processing
long noncoding RNAs- no known function typically

Question 21

CRISPR mechanism

Answer 21

1. bacteria put a piece of pathogen’s genome into their CRISPR array
2. if the pathogen attacks again, they’ll transcribe their array
3. transcript matching invader’s genome will pair with CAS protein to form effector complex
4. effector complex cuts invader DNA

Question 22

Xist

Answer 22

long noncoding RNA that coats the X chromosome destined for inactivation in bio. females

Question 23

collinearity

Answer 23

number of nucleotides is proportional to number of amino acids- not completely true

Question 24

how are introns removed from RNA?

Answer 24

via RNA splicing in the nucleus

Question 25

shine-dalgrano sequence

Answer 25

ribosome binding site during translation in bacteria

Question 26

what do small RNAs do?

Answer 26

transcription
translation
cancer
research
development
gene expression
formation of chromatin structure
defense against foreign DNA