nucleic Acids dna

Question 1

Describe the role of DNA polymerase in DNA replication

Answer 1

Joins nucleotides (to form new strand)

Question 2

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

Answer 2

Watson and Crick

Question 3

Role of single stranded DNA fragments and DNA nucleotides in semi-conservative replication

Answer 3

Template
Determines order of nucleotides

Forms complementary pairs A-T/C-G

Question 4

Other than being smaller, give two ways in which prokaryotic DNA is different from eukaryotic DNA.

Answer 4

Prokaryotic DNA is circular, SMALLER/SHORTER , not associated with histones and has no introns

Question 5

Deacribe the main role of DNA (2)

Answer 5

• Carries the genetic code
• instructions for making proteins/codes for primary structure of proteins
Controls cells activities

Question 6

The nucleic acid which never leaves the nucleus in a eukaryotic cell is…

Answer 6

DNA

Question 7

Grasshoppers and humans have very similar percentages of each base in their DNA but are not the same class of organism. Use your knowledge of Dna structure and function to explain this

Answer 7

•Grasshoppers and humans have a different sequence of bases which therefore produce different proteins

Question 8

Describe the term frame-shift mutation and evaluate impact of this mutation on phenotype of the organism

Answer 8

A frame shift mutation is

• A deletion or addition of a base
• That occurs during DNA replication
• Causes all downstream triplets to shift by one base

EFFECTS
• It results in a different protein being synthesised
• Likely loss of function for that gene or possible new function arising from the new protein
• If mutation occurs in an intron, it is possible that there is no effect

Question 9

Suggest why most mutations in eukaryotic cells are regarded as neutral

Answer 9

• The mutation has no effect on the phenotype of the organism
• They occur in the genes are not expressed in that cell
• They occur in introns
• They are silent mutations

Question 10

Identify 2 environmental factors that increase rate of mutation and describe their interaction with DNA

Answer 10

DNA reactive chemicals such as some bacteria viruses

• High energy ionising radiation E.g- X-rays and gamma rays
• Toxic chemicals such as benzene bromine
• They interfere with base pairing

Question 11

The 2 strands of DNA are described as antiparallel. Explain meaning of antiparallel

Answer 11

Two strands run alongside each other, but in opposite directions

Question 12

Why can nucleotides only be added in a 5’ to 3’ direction

Answer 12

• DNA polymerase has a specific active site that only binds to the 5’ , 5’ and 3’ are different shapes

Question 13

Suggest a structural feature of DNA that boosts its protection from chemical attack

Answer 13

• Dna has a double helix
• so compact

Question 14

Compare the structures and functions of DNA and RNA

Answer 14

FUNCTIONS
• Dna carries genetic information WHEREAS Rna transfers the genetic information to the ribosomes
SIMILARITIES
• Both are polymers of nucleotides
• Both have phosphodiester bonds/sugar phosphate backbone
• Both have 4 bases
DIFFERENCES
• DNA contains deoxyribose sugar whereas Rna contains ribose sugar
• Rna molecules are smaller than DNA
• DNA contains thymine bases, RNA contains uracil bases

Question 15

Other than use for replication, give one advantage of DNA molecules having 2 strands

Answer 15

• Provides stability
• protects bases (from mutations)

Question 16

Describe and explain the structure of DNA

Answer 16

-sugar phosphate backbone/double stranded so provides strength/stability/protects bases
• large molecule so can store lots of information
• helical- so compact
• base sequence allows information to be stored
• Double stranded so replication can occur semi-conservatively
• Complementary base pairing (A-T and C-G) so accurate replication
• many hydrogen bonds so stable

Question 17

Why does DNA replicate semi-conservatively

Answer 17

• This ensures genetic continuity

Question 18

Mesellson and Stahl experiment steps

Answer 18

•Bacteria were cultured on a heavy nitrogen (15N) medium
•Bacteria took up this nitrogen and used it to synthesise DNA bases
•After the Dna is extracted and spun in a centrifuge it settled near the bottom of the tube
• The bacteria is then transferred to light nitrogen medium
• After period of time DNA extracted and centrifuged, it settled in an intermediate position

Question 19

Describe how a change in the base sequence of the DNA coding for an enzyme may result in a non-functional protein

Answer 19

• Change in primary structure changes sequence of amino acids
• So hydrogen,disulphide and ionic bonds form in different positions
• This alters the tertiary structure of the enzyme
Active site no longer complementary to substrate
• So no E-Z complexes can be formed

Question 20

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

Answer 20

1. Weak / easily broken hydrogen bonds between bases allow two strands to separate / unzip;
2. Two strands, so both can act as templates;
3. Complementary base pairing allows accurate replication

Question 21

Differences between DNA and RNA

Answer 21

DNA has deoxyribose, thymine, and is double-stranded. RNA has ribose, uracil, and is single-stranded

Question 22

State and explain the property of water that can help to buffer changes in temperature

Answer 22

Water has high specific heat capacity.
So it takes a lot of energy to change temperature.

Question 23

Humans synthesise more than their body mass of ATP each day. Explain why it is necessary for them to synthesise such a large amount of ATP. (2)

Answer 23

•ATP is an immediate source of energy
•ATP only releases a small amount of energy at a time

Question 24

Explain 5 properties of water

Answer 24

Metabolite in condensation reactions
A solvent so metabolic reactions can occur
High specific heat capacity so buffers changes in temperature
Latent heat of vaporisation so provides a cooling effect
Cohesion so supports columns of water
Cohesion so produces surfaces tension for small organisms

Question 25

Describe semi-conservative replication

Answer 25

DNA helicase unwinds DNA by breaking hydrogen bonds
Both strands act as template
Free nucleotides line up in complementary pairs
Dna polymerase joins nucleotides
Forming phosphodiester bonds
Each new DNA molecule consists of one old and one new strand

Question 26

Describe how an ATP molecule is formed

Answer 26

ADP + PI
Condensation reaction
Using atp synthase

Question 27

Describe structure of DNA

Answer 27

Polymer of nucleotides;
2. Each nucleotide formed from deoxyribose, a phosphate (group) and an organic/nitrogenous base;
3. Phosphodiester bonds (between nucleotides);
4. Double helix/2 strands held by hydrogen bonds;
5. (Hydrogen bonds/pairing) between adenine, thymine and cytosine, guanine;
5

Question 28

2 uses of atp

Answer 28

Provides energy for AT, protein synthesis

Phosphorylation: binds to enzymes or substrates and lowers Ea by altering 3• or making molecules more reactive

Question 29

ATP is useful because

Answer 29

Released in small amounts
Immediate energy compound
Phosphorylates molecules
Can be made again

Question 30

Give 2 ways in which ATP is a suitable energy source for cells to use

Answer 30

• Releases small amounts of energy so little amount of energy lost as heat
• Releases energy instantaneously

Question 31

Give 2 advantages of ATP as an energy storage molecule within a cell

Answer 31

• Does not pass out of the cell
• Releases energy instantaneously
• Releases energy in small amounts
So little energy lost as heat

Question 32

Humans synthesise more than their body mass of ATP each day. Explain why it is necessary for them to synthesise such a large amount of ATP. (2)

Answer 32

•ATP is an immediate source of energy
•ATP only releases a small amount of energy at a time