B1.2 - DNA

Question 1

what is a chromosome?

Answer 1

a tightly packed molecule of DNA containing genes

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)

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

double helix structure

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

definition of mRNA?

Answer 10

a single strand copy of DnA
(messenger RNA)

Question 11

describe the process of transcription (6)

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 (mRNA formed)
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 codon 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 from optimal pH affect enzyme controlled reactions? (3)

Answer 25

• enzymes DENATURE (1)
• which would cause the active site to change (1)
• which would decrease the rate of enzyme controlled reactions (1)

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)