B1.2 - DNA

Question 1

what is a chromosome?

Answer 1

a long molecule of DNA

Question 2

how many chromosomes are in human cells?

Answer 2

46

Question 3

define clones

Answer 3

organisms that share identical DNA

Question 4

define genes

Answer 4

short sections of DNA that code for a specific characteristic (ie. eye colour)

(Your answer was wrong on a past paper markscheme = they said ignore that answer this is what your supposed to say)

A length of DNA that codes for a protein

Question 5

where (within DNA), would a gene be found?

Answer 5

within a chromosome

Question 6

what is the structure of DNA?

Answer 6

• Two strands
• Twisted in a double helix
• small units called nucleotides
• therefore is a polymer
• has complimentary base pairings
• base/phosphate group/deoxyribose sugar

Question 7

what does thymine attatch onto?

Answer 7

adenine

Question 8

what does cytosine join onto?

Answer 8

guanine

Question 9

draw a nucleotide

Answer 9

a pentagon in the centre -> deoxyribose sugar
rectangle on the RH side -> base
circle on the LH (diagonal) -> phosphate group

Question 10

what is mRNA?

Answer 10

a single strand copy of DnA

messenger RNA

Question 11

describe the process of transcription

Answer 11

1) In the nucleus DNA around gene unzips
2) both strands are separated
3) one strand acts as a template and complimentary base pairings attach to the strand being copied
4) strand of mRNA detached itself from DNA template
5) DNA zips back up
6) mRNA moves out of nucleus to ribosomes in cytoplasm

Question 12

which base is not present in mRNA, and so what other base is created?

Answer 12

no thymine, so uracil binds with adenine

Question 13

why is mRNA produced?

Answer 13

as DNA is too large to leave the nucleus

Question 14

what is the purpose of the process named ‘translation’?

Answer 14

making new proteins

Question 15

what determines the type of protein made?

Answer 15

the order of nucleotides/animo acids

Question 16

describe the process of translation

Answer 16

1) ribosomes read nucleotides on mRNA in codons/ base triplets (which codes for a specific animo acid)
2) adds the corresponding animo acid
3) continues to read triplet code and adds more and more animo acids
4) animo acids join together in a chain, and fold (protein)

Question 17

what determines how a protein will fold?

Answer 17

the sequence of animo acids

Question 18

define an enzyme

Answer 18

a biological catalyst (can repeatedly be used for same reaction, asthey are not used up)

Question 19

describe two uses of enzymes

Answer 19

• build larger molecules from smaller ones

- break down larger molecules to smaller ones

Question 20

define an active site

Answer 20

the area where molecules of other substances bind to the enzyme

Question 21

what does it mean when an enzyme is highly specific?

Answer 21

it can only bind to one type of substrate molecule (active site is a specific shape)

Question 22

describe the lock & key hypothesis

Answer 22

the idea that only one key can unlock a lock.

lock is enzyme, key is substrate

(CHECK WHETHER YOU KNOW WHICH ONE IS WHICH)

Question 23

what factors affect enzymes-catalysed reactions?(explain all in your head summarised)

Answer 23

• temperature
• pH
• amount of substrate
• amount of enzymes

Question 24

what happens to enzymes when temperatures become too high?

Answer 24

they begin to unravel (active site changes, cannot be used any more)

• DENATURE *

Question 25

how does a change in pH affect enzyme controlled reactions?

Answer 25

• it can break/affect the bond between animo acids
• which would cause the active site to change
• causes enzyme to DENATURE

Question 26

can enzymes still catalyse reactions when they begin to denature?

Answer 26

yes, the reaction would be slower, but as long as the substrate can roughly fit in the active site the reaction can be carried out

Question 27

Define optimum conditions

Answer 27

• Conditions in which the enzyme can catalyse fastest - highest rate of reactions
• (when substrate and enzyme have the most successful collisions)

Question 28

Where is bile produced and stored?

Answer 28

Produced in the liver, stored in the gall bladder

Question 29

What does bile do?

Answer 29

Neutralises acid from the stomach (as enzymes in the small intestine work better in alkaline conditions)

Question 30

The rate of gas produced at 30 °C is greater than at 25 °C.

Use ideas about enzymes to explain why.

Answer 30

• increased movement of molecules / increased kinetic energy 
• therefore, more chance of substrate colliding with enzymes/active sites 
• more chance of substrate entering active site 

ALLOW more enzyme-substrate complexes forming

Question 31

how pH affects enzymes

Answer 31

Many amino acids in an enzyme molecule carry a charge. Within the enzyme molecule, positively and negatively charged amino acids will attract. This contributes to the folding of the enzyme molecule, its shape, and the shape of the active site.

Changing the pH will affect the charges on the amino acid molecules. Amino acids that attracted each other may no longer be. Again, the shape of the enzyme, along with its active site, will change.

Extremes of pH also denature enzymes. The changes are usually, though not always, permanent

Question 32

3 marks - pH on enzymes

Answer 32

• change in pH affects the interactions between amino acids in a chain
• this may make the enzyme unfold, changing the shape of the active site
• the enzyme is denatured

Question 33

3 marks - increasing substrate conc.

Answer 33

• in general higher substrate concentration, faster the rate of reaction
• at certain substrate concentration, all the enzyme molecules are bound to substrate molecules (point of saturation)
• rate of reaction is at its maximum — any further increase in the number of substrate molecules will not increase the rate of reaction as there are no enzymes for them to bind to

Question 34

3 marks, increasing enzyme concentration

Answer 34

• in general, higher enzyme concentration = faster rate of reaction
• but limited by substrate conc.
• if no new substrate molecules are added, the reaction will stop