Chapter 14

Question 1

Gene expression to form a specific polypeptide takes two steps:

Answer 1

Transcription

Translation

both are the central dogma of molecular bio

Question 2

Transcription

Answer 2

copies information from a DNA sequence to a complementary RNA sequence (MRNA)

Question 3

Translation

Answer 3

converts RNA sequence to amino acid sequence of a polypeptide
(trna lines up amino acids into protein)

Question 4

RNA (ribonucleic acid) differs from DNA:

Answer 4

• usually only one polynucleotide strand
• sugar is ribose
• contains uracil instead of thymine

Question 5

Three types of RNA in protein synthesis:

Answer 5

mRNA
tRNA
rRNA

Question 6

mRNA

Answer 6

carries copy of a dna sequence to site of protein synthesis at the ribosome

Question 7

tRNA

Answer 7

carries amino acids for polypeptide assembly

Question 8

rRNA

Answer 8

catalysis of peptide bonds and provides structure

Question 9

What does mRNA do ?

Answer 9

forms a complementary copy of one Dna strand in gene

travels from nucleus to cytoplasm carrying info as codons

associates with ribosome and tRNA anticodons

Question 10

transcription component:

Answer 10

A DNA template- one of the two strands
nucleotide triphosphates
RNA polymerase enzyme

Question 11

what does the RNA polymerase enzyme do

Answer 11

-catalyzed synthesis of RNA

Question 12

Transcription occurs in 3 phases

Answer 12

1. initiation: Ran polymerase binds to promoter
2. Elongation: Ran poly. unwinds DNA
   - synthesizes transcript
3. Termination
   specific stop sequence
   ran poly. disengages

Question 13

what is the genetic code?

Answer 13

specifies which amino acids will be used to build a protein

redundant - many codons are same amino acids) (not ambiguous - one codon one amino acid

Question 14

what is a codon/

Answer 14

sequence of three bases- each specifies a specific amino acid

Question 15

start codon:

Answer 15

AUG - initiation signal for translation

Question 16

Stop codons:

Answer 16

UAA, UAG, UGA - stop translation

Question 17

noncoding sequences are:

Answer 17

introns

Question 18

coding sequences are:

Answer 18

exons

Question 19

introns and eons appear in

Answer 19

primary mRNA transcript

Question 20

how are introns removed

Answer 20

by splicosome from the final mRNA

Question 21

two key events to ensure protein made is the specified one from mRNA:

Answer 21

1. tRNAs must read mRNA codons correctly

2. tRNAs must deliver amino acids corresponding to each codon

Question 22

functions of tRNA

Answer 22

• binds to amino acid
• associate with mRNA
• interact with ribosome

Question 23

what is the amino acid attachment site?

Answer 23

3’ end - binds covalently

Question 24

anticodon:

Answer 24

at the midpoint of tRNA sequence- site of base paring with mRNA
-unique for each tRNA

Question 25

Example for anticodon

Answer 25

DNA codon for arginine: 3′-GCC-5′

Complementary mRNA: 5′-CGG-3′

Anticodon on the tRNA: 3′-GCC-5′. This
tRNA is charged with arginine.

Question 26

ribosome

Answer 26

hold mRNA and charged tRNAs in correct positions to allow assembly of polypeptide chain

• two subunits -large and small
• held together by ionic and hydrophobic forces
• only held together when active

Question 27

Large subunit has 3 tRNA binding sites:

Answer 27

A (amino acid) site binds with anticodon of charged tRNA
P (polypeptide) site where tRNA adds its amino acid to the growing chain
E (exit) site where tRNA sits before being released from ribosome

Question 28

translation occurs in 3 steps:

Answer 28

initiation - complex forms
Elongation - second charged tRNA enters P site
-peptide bond formation
Termination - stop codon enters A site

Question 29

post translational aspects:

Answer 29

polypeptide emerges and fold into 3-d shape

conformation allows it to interact with other molecules - it may contain a signal sequence indicating where in the cell it belongs

can be chemically modified