2.1.3 DNA Replication & the Genetic Code

Question 1

Nucleotides

Answer 1

• pentose monosaccharide
• phosphate group
• nitrogenous base

Question 2

Nucleic acid

Answer 2

Nucleotides linked in condensation reactions

Phosphodiester bonds formed (5’3’)

Sugar-phosphate backbone

Question 3

DNA

Answer 3

Two strands - double helix
Deoxyribose
Anti-parallel strands
ATGC

Backbone=stable, coiled
Helix=compact, more info, based protected
Base pairing=replicated accurately

Question 4

RNA

Answer 4

Single stranded
Ribose
AUGC

Corresponds to one gene

Question 5

Base pairing rules

Answer 5

Complementary:
A+T form 2H-bonds
G+X form 3H-bonds

Small pyramidine + larger purine (constant distance)

Purine (2 rings) A and G
Pyramidine (1 ring) T/U and C

Question 6

Semi-conservative replication of DNA

Answer 6

• double helix unwinds and unzips
• free DNA nucleotides pair w complementary bases (H-bonds formed)
• two new molecules of DNA formed (one old one new)

DNA helicase = unwinds and unzips, travels along DNA backbone, breaks H-bonds between bases
DNA polymerase = catalyses formation of phosphodiester bonds between nucleotides

Question 7

Codon

Answer 7

Sequence of three bases

Codes for one amino acid

Question 8

Gene

Answer 8

Section of DNA that contains compete sequence of codons to code for an entire protein

Question 9

Transcription (protein synthesis)

Answer 9

Sense/coding strand = 5’ to 3’ codes for the protein

Antisense/template strand = 3’ to 5’ complementary copy, doesn’t code

Nucleotides attach to template strand

RNA formed = same as sense/coding strand

Question 10

Translation (protein synthesis)

Answer 10

1) mRNA binds to small subunit of ribosome at start codon (AUG)
2) tRNA w complementary anticodon binds to the mRNA start codon
3) another tRNA binds to next codon
4) first AA is transferred onto the AA on the 2nd tRNA — formation of peptide bond (peptidyl transferase)
5) rivosome moves along mRNA, releasing 1st tRNA

Question 11

Ribosomes

Answer 11

Two subunits: one large one small

Composed of protein and tRNA (for maintaining structural stability

Question 12

ATP

phosphorylated nucleotide

Answer 12

• three phosphate groups
• pentose sugar
• a nitrogenous base (always adenine)

Question 13

Why do cells need energy?

Answer 13

• synthesis
• transport
• movement

Question 14

How ATP releases energy

Answer 14

Hydrolysis: (requires water)

ATP + H2O —> ADP + Pi + energy

Reaction coupled w energy-requiring reactions
(Inorganic phosphate)

Question 15

Properties of ATP

Answer 15

Small — easily moved
Water soluble — aqueous environ.
Bonds between phosphates contain lots of energy
Energy released in small quantities
Easily regenerated