chapter 2

Question 1

general structure of nucleotides

Answer 1

• phosphate group
  -pentose sugar
  -nitrogen-containing base

Question 2

differences between the DNA and RNA nucleotides

Answer 2

• DNA has deoxyribose, RNA has ribose
• RNA has uracil instead of thymine

Question 3

how does nucleotides join together to form DNA/RNA polymers

Answer 3

by condensation reaction
phosphodiester bond - between pentose sugar and phosphate group

Question 4

mRNA function

Answer 4

carry a copy of genetic code of one gene to a ribosome in the cytoplasm

Question 5

tRNA function

Answer 5

carriers specific amino acids to the mRNA on the ribosome

Question 6

rRNA

Answer 6

combines with proteins to form a ribosome

Question 7

DNA structure

Answer 7

Polymer of nucleotides;
Each nucleotide formed from deoxyribose, a phosphate (group) and an organic/nitrogenous base;
Phosphodiester bonds (between nucleotides);
Double helix held by hydrogen bonds;
(Hydrogen bonds/pairing) between adenine, thymine and
cytosine, guanine;

Question 8

Name the two scientists who proposed models of the chemical structure of DNA and of DNA replication.

Answer 8

Watson and Crick

Question 9

Give two features of DNA and explain how each one is important in the semi-conservative replication of DNA.

Answer 9

• easily broken hydrogen bonds between bases allow two
  strands to separate
  -Two strands, so both can act as templates;
  -may appear in the same feature
  Complementary base pairing allows accurate replication

Question 10

Describe the role of two named enzymes in the process of semi conservative replication of DNA.

Answer 10

DNA helicase causes breaking of hydrogen between DNA
strands
DNA polymerase joins the DNA nucleotides
Forming phosphodiester bonds;

Question 11

Contrast the structures of ATP and a nucleotide found in DNA

Answer 11

ATP has ribose and DNA nucleotide has
deoxyribose;
ATP has 3 phosphate (groups) and DNA
nucleotide has 1 phosphate (group);
ATP – base always adenine and in DNA
nucleotide base varies

Question 12

explain why the arrows point in opposite directions in DNA replication

Answer 12

DNA has antiparallel strands
nucleotides aligned differently
Enzymes have active sites with specific shape;
Only substrates with complementary shape can bind with active site of DNA polymerase

Question 13

Semi conservative replication

Answer 13

ensures genetic continuity between generation of cells

• The DNA unwinds, then DNA helices breaks the hydrogen bonds between the complimentary base pairs
• the double helix unwinds and separates the two strands of DNA
• new DNA nucleotides bind to exposed bases on the DNA template strand
• DNA polymerase catalyses the condensation reaction that joins adjacent nucleotides

Question 14

properties of water

Answer 14

1- is metabolite- can take part in condensation reaction, hydrolysis and photosynthesis

2- its the solvent where metabolic reaction take place

3- has a relative high heat capacity- buffers temperature changes

4- relative large latent heat of vaporisation- losing small amounts of water through evaporation has a cooling effect

5- strong cohesion between water molecules- support of water columns of water in xylem for the transpiration stream and produce