biochemistry of nucleic acids

Question 1

nucleoside:

Answer 1

base and 5 carbon sugar

Question 1

nucleotide:

Answer 1

nucleoside and phosphate group

Question 2

purines:

Answer 2

adenine and guanine

Question 3

pyrimidines:

Answer 3

cytosine, thymine, uracil

Question 4

Phosphodiester bonds:

Answer 4

form between 3’ OH group and 5’ triphosphate, link nucleotides

Question 5

describe the DNA structure

Answer 5

• Anti-parallel double helix
  
  • One strand 5’ to 3’, other strand 3’ to 5’
• Sugar-phosphate backbone
• Base pairs in the inside, held together with H bonds

Question 6

describe the process of DNA replication

Answer 6

1. DNA primer required
2. Helix unwound by helicase
3. Replication fork with leading and lagging strand
4. Leading synthesized in 5’→ 3’ direction - catalyzed by DNA polymerase
5. Lagging is synthesized in Okazaki fragments which are then joined by DNA ligase

Question 7

what are the origins of replication

Answer 7

• In eukaryotes, replication starts simultaneously at several points in the genome
• Speeds up replication
• Bidirectional

Question 8

rRNA:

Answer 8

combines with proteins to form ribosomes

Question 9

tRNA:

Answer 9

carries amino acids to be incorporated into protein

Question 10

mRNA:

Answer 10

carries genetic information for protein synthesis

Question 11

describe RNA polymerase

Answer 11

• Multi-subunit complexes which make RNA
• Eukaryotes have 3 types: Pol I, Pol II, Pol III
• Pol II synthesizes all mRN

Question 12

Premature → mature mRNA

Answer 12

• Splice out introns (exons = coding, intron = non-coding)
• Add poly-adenosine tail
• Add 5’ cap

Question 13

translation Initiation-

Answer 13

formation of initiation complex, energy provided by GTP

Question 14

translation Elongation-

Answer 14

anticodons of tRNA form base pairs with codons on mRNA, aminoacyl-tRNA synthetases catalyse the covalent attachment of amino acids to their corresponding tRNA molecules

Question 15

translation Peptide bond formation and translocation-

Answer 15

peptidyl transferase catalyzes peptide bond formation between amino acids in P and A sites, EF-2 moves ribosome along mRNA

Question 16

translation Termination-

Answer 16

A site encounters stop codon, termination protein binds to the codon and the ribosome dissociates, leads to a change in peptidyl transferase activity which results in the release of the protein from the last tRNA to which it was attached

Question 17

Post-translational modifications

Answer 17

• Glycosylation
• Disulphide bods (ER)
• Folding/assembly of multi-subunit proteins (ER)
• Specific proteolytic cleavage (ER, Golgi, secretory vesicles)

Question 18

Features of the genetic code

Answer 18

• Degenerate
• Unambiguous
• Near universal

Question 19

Point mutations:

Answer 19

change in single base in DNA

Question 20

Nonsense mutation:creates new termination codon

Answer 20

creates new termination codon

Question 21

Missense mutation:

Answer 21

results in change of amino acid sequence

Question 22

Silent mutation:

Answer 22

no change of amino acid sequence

Question 23

Frameshift mutation:

Answer 23

addition or deletion of 1 or 2 bases which changes the reading frame of translation

Question 24

describe the leading strand

Answer 24

• always has a free 3’ end

Other strand has to be replicated in short segments

Question 25

transcription 1

Answer 25

TATA box at (-25) - TATA box binding protein introduces a kink into DNA to determine the start and direction of transcription and provides landing platforms for further transcription factors and RNA pol

Question 26

transcription 2

Answer 26

2. TFIID - first general transcription factor to bind to the promotor, binds to TATA box through TBP
   
   1. General transcription factor required for all Pol II transcribed genes

Question 27

transcription 3

Answer 27

RNA poly II binds specific promotor (0)

Question 28

transcription 4

Answer 28

Transcription belongs at nucleotide +1

Question 29

transcription 5

Answer 29

DNA chain separation - unwinding of DNA, catalyzed by helicase

Question 30

transcription Initiation-

Answer 30

selection of first nucleotide of growing RNA
- Requires additional general transcription factors

Question 31

transcription elongation

Answer 31

addition of further nucleotides to RNA chain in the 5’→ 3’ direction

Question 32

transcription termination

Answer 32

release of finished mRNA