Chapter 17 - Expression of Genes

Question 1

functional RNA

Answer 1

tRNA, rRNA

Question 2

central dogma

Answer 2

explanation of the flow of genetic material:
DNA –> RNA –> protein
transcription & translation

Question 3

Beadle and Tatum’s experiment

Answer 3

• bombarded red bread mold with X-rays
• analyzed relationship between metabolic pathway of arginine biosynthesis and mutated genes
• explained the “one gene one enzyme” hypothesis

Question 4

degeneracy/redundancy of codons

Answer 4

many-to-one structure-function relationship

e.g. more than on codons (synonymous codons) code for a particular amino acid

Question 5

Sense strand

Answer 5

(coding strand)

• DNA strand that is not used for mRNA transcription
• directed in 5’-3’ direction
• contains same sequence as mRNA (except T)

Question 6

Antisense strand

Answer 6

(non-coding, template strand)

• template used for transcription to make mRNA
• antisense because its direction is 3’-5’ as the mRNA needs to be transcribed in 5’-3’ direction

Question 7

Start codon

Answer 7

AUG - methionine

Question 8

Stop codon

Answer 8

UAA / UAG /UGA

Question 9

Site of transcription

Answer 9

eukaryotes - in the nucleus

prokaryotes - in the cytoplasm (nucleoid region)

Question 10

RNA polymerase (II)

Answer 10

• enzyme for transcription
• binds to promoter region on DNA
• acts like helicase: unwinds DNA double helix
• acts like DNA polymerase III: adds RNA nucleotides to 3’ OH end of transcript

Question 11

Transcription factors

Answer 11

mediate binding of RNA polymerase
+
initiation of transcription

1) general TF - responsible for all transcriptions in every cell
2) specific TF - works specifically at specific time in a specific cell

Question 12

Stages of transcription

Answer 12

1) Initiation
- formation of transcription initiation complex
a) RNA polymerase (II) on promotor
b) general, specific transcription factors
c) transcription unit - DNA region downstream of promotor

2) Elongation
- RNA polym II moves along template strand and adds complementary RNA nucleotides to 3’ OH end of transcript

3) Termination
a) in prokaryotes: terminator sequence transcribed, RNA polymerase detaches from DNA template
b) in eukaryotes: polyadenylation signal recognized by nuclease which cleave mRNA from RNA polymerase II

Question 13

RNA processing in eukaryotes

Answer 13

1) 5’ capping
- adding modified guanine to 5’ end of pre-mRNA
2) 3’ poly A tail
- adding 50-250 adenine nucleotides to 3’ OH end of pre-mRNA
3) RNA splicing

Question 14

Intron

Answer 14

INTervening RegiON

• non-coding segments
• removed during RNA splicing
• increases probability of crossing over

Question 15

Exon

Answer 15

Expressed regiON

-coding segments

Question 16

5’ capping

Answer 16

method of RNA processing in eukaryotes

• adding modified guanine to 5’ end of pre-mRNA
• role: protect mRNA from nuclease, promote export of mRNA through nuclear pore

Question 17

3’ poly A tail

Answer 17

method of RNA processing in eukaryotes

• adding 50-250 adenine nucleotides to 3’ OH end of pre-mRNA
• role: protect mRNA from nuclease, promote export of mRNA through nuclear pore

Question 18

RNA splicing

Answer 18

method of RNA processing in eukaryotes
(occurs in spliceosome - complex of protein & DNA)
-ribozyme removes introns in pre-mRNA
-keeps axons

Question 19

Alternative RNA splicing

Answer 19

• 2+ final mRNA produced from single mRNA
• depends on which segments are treated as exon/intron
• increase genetic diversity

Question 20

Large scale mutation

Answer 20

1) alteration in chromosome number
a) aneuploidy (2n+1, 2n-1)
b) polyploidy (3n, 4n etc.)

2) Alteration in structure of chromosome
a) deletion
b) duplication
c) inversion
d) translocation - fragments of one chromosome exchanged with non-homologous chromosome

Question 21

Small scale mutation

Answer 21

point mutation (changes in one/few nucleotide pairs)
1) nucleotide pair substitution (during DNA rep and DNA repair)
a) silent - no effect (change to synonymous codon)
b) missense - original codon changed to different codon, different amino acid formed
e.g. wild type beta- globin (glutamine) to sickle cell beta globin (valine)
c) nonsense - original codon changed to stop codon
(UAA, UAG, UGA), produced premature polypeptide

2) nucleotide pair insertion/deletion
- causes frameshift

Question 22

tRNA

Answer 22

• functional RNA
• contains anticodon
• transfer amino acid from cytoplasmic pool to ribosome
• clover shaped (2D), L shaped (3D)
• approximately 20 different tRNAs

1) empty (uncharged) tRNA - no amino acid on 3’ end
2) charged (aminoacyl) tRNA - amino acid attached to 3’ end
3) peptide tRNA - many amino acids attached to 3’ end

Question 23

aminoacyl tRNA synthetase

Answer 23

covalently bonds tRNA with corresponding amino acid

• amino acid and uncharged tRNA enters active site
• forms aminoacyl (charged) tRNA

Question 24

ribosome for translation

Answer 24

-composed of rRNA and protein

a) large subunit
- EPA sites
b) small subunit

Question 25

Translation process

Answer 25

1) initiation
- forms translation initiation complex (mature mRNA, initiator tRNA (methionine), ribosome)
- small ribosomal subunit binds to mRNA
- large ribosomal subunit binds
- hydrolysis of GTP provides energy for assembly
- initiator tRNA bonds to start codon

2) elongation
a) codon recognition
b) peptide bond formation between amino acids
c) translocation of ribosome

3) termination
- occurs when stop codon (UAA, UAG, UGA) reaches A site of ribosome
- releasing factor binds to A site and promotes hydrolysis of initiation complex

Question 26

translation initiation complex

Answer 26

1) mature mRNA
2) initiator tRNA (start codon AUG - methionine)
3) ribosome (P site)

Question 27

polyribosome

Answer 27

simultaneous translation - where several ribosome are attached to single mRNA