Unit 14- RNA

Question 1

gene organization

Answer 1

• concept of colinerarity and noncolinearity
• # of nucleotides in a gene should be proportional to the # of amino acids in encoded protein
• DNA much longer than mRNA (hybridization)
• bacteria = colinear; eukaryotes = noncolinear (loops)

Question 2

colinearity

Answer 2

continuous seq of nucleotides in DNA encodes a continuous sequence of amino acids in a protein

Question 3

introns

Answer 3

• eukaryotes have introns and exons
  -later REMOVED by RNA processing
• # and size vary between genes
• common in eukaryotes; uncommon in bacteria

Question 4

group 1 introns

Answer 4

• Location: some rRNA genes
• mechanism: self-splicing

Question 5

group 2 introns

Answer 5

• Location: protein-encoding genes in mitochondria and chloroplast
• mechanism: self-splicing

Question 6

nuclear-premRNA introns

Answer 6

• Location: protein-encoding genes in the nucleus of eukaryotes
• mechanism: spliceosomal (snRNA)

Question 7

tRNA introns

Answer 7

• Location: tRNA genes
• mechanism: enzymatic

Question 8

gene

Answer 8

• DNA sequences that code for all exons and introns
• Sequences at the beginning and end of the RNA are not translated into a protein
  -The promoter
  -The terminator

Question 9

structure of RNA

Answer 9

• mature mRNA contains 5’ untranslated region (5’ UTR, or leader seq)
• Shine-Dalgarno seq (prokaryotes)
• protein-coding region
• 3’ untranslated region
  (3’ and 5’: stability and reg of translation NOT aa encoding)

Question 10

start codon

Answer 10

AUG (met)

Question 11

stop codons

Answer 11

• UAA
• UAG
• UGA

Question 12

pre-mRNA processing

Answer 12

• addition of 5’ cap: nucleotide with 7-methylguanine; 5’-5’ bond to 5’ end
• addition of poly(A) tail: 50-250 adenine nucleotides added to 3’ end

Question 13

5’ cap

Answer 13

facilitates bingind of ribosomes to 5’ end of mRNA, increasing mRNA stability

Question 14

3’ clevage and addition of poly(A) tail

Answer 14

inc stability of mRNA, facilitates binding of ribosomes

Question 15

RNA splicing function

Answer 15

removes noncoding introns, facilitates mRNA export to cytoplasm, allows mult protein production from alt splicing

Question 16

RNA editing

Answer 16

alters nuckeotide seq of mRNA

Question 17

RNA splicing

Answer 17

consensus seq
- 5’ consensus seq: GU(A/G): 5’ splice site
- 3’ consensus seq: CAGG
- branch point: adeine “A”: ~18-40 nucleotides upstream of 3’-splicing site

spliceosome: five RNA molecules +300 proteins

Question 18

steps of splicing

Answer 18

1. 5’ end cleaves from the upstream exon and attatched to branch point to form a LARIAT
2. 3’ end of intron is cleaved from downstream exon, and ends of the 2 exons are spliced together

• takes place in spiceosome

Question 19

nuclear organization

Answer 19

• intron removal, mRNA processing, and transcription take place at same site in nucleus

Question 20

minor splicing

Answer 20

• 2-tpes of self-splicing introns: group 1 and 2 (due to complez secondary structure)
• occur in some protist rRNA and in fungi mitochondria

Question 21

alt processing pathways for processing pre-mRNA

Answer 21

• enables exons to be spliced together in different combinations to yield different proteins
• due to Multiple 3’ cleavage sites

Question 22

RNA editing

Answer 22

• guide RNA pairs with mRNA
• template for addition, deletion, or alteration of bases

Question 23

structure of tRNA

Answer 23

• rare modified RNA nucleotide bases (robothymine and pseudouridine)
  
  • produced by chem alt of standard bases
• common secondary structure: cloverleaf
• anticodon

Question 24

structure of ribosome

Answer 24

• large ribosome subunit
• small ribosome subunit

Question 25

ribosomal RNA is processed after transcription

Answer 25

- methyl groups added - RNA cleaved into several pieces - trimmed - mature rRNA molecules(subunits) produced

Question 26

RNA interfering

Answer 26

limits the invasion of foreign genes and censors the expression of their own genes

Question 27

Long Noncoding RNAs

Answer 27

- do not encode proteins - control gene expression - enhancer RNAs are transcribed from enhancers and control gene expression