unit 1 key area 3

Question 1

how is a cells genotype determined

Answer 1

by the sequence of DNA bases in its genes

Question 2

how is a cells phenotype determined

Answer 2

by the proteins that are synthesised when these genes are expressed

Question 3

what processes does gene expression involve

Answer 3

transcription and translation

Question 4

are all genes in a cell expressed

Answer 4

no, only a fraction

Question 5

what can affect gene expression

Answer 5

environmental factors acting inside and outside the cell

Question 6

where are proteins found in a multicellular organism

Answer 6

throughout the organism

Question 7

what is an example of a protein

Answer 7

muscle, hair, cell membranes

Question 8

what are proteins used for

Answer 8

growth and repair

Question 9

what elements make up a protein

Answer 9

carbon, hydrogen, oxygen, nitrogen

Question 10

what is the sub unit proteins (polypeptides) are made from and the bond that holds them together

Answer 10

amino acids joined by peptide bonds

Question 11

what does a polypeptide chain form

Answer 11

proteins which give the cell its structure and help control its function

Question 12

what causes the 3 dimensional shape of a protein to allow it to function

Answer 12

hydrogen bonds and other interactions form between certain amino acids causing the chain to become coiled/folded

Question 13

what determines the function of a protein

Answer 13

their large variety of shapes

Question 14

what are the main differences that RNA has compared to DNA

Answer 14

one strand, adenine - uracil, ribose sugar

Question 15

what are the three types of RNA involved in transcription and translation which gene expression relies on

Answer 15

messenger RNA (mRNA)
transfer RNA (tRNA)
ribosomal RNA (rRNA)

Question 16

what is the function of mRNA

Answer 16

to carry a complementary copy of the genetic code from the DNA in the nucleus to the ribosome in the cytoplasm

Question 17

what are each triplet of bases on mRNA called and what are their function

Answer 17

codon - codes for one specific amino acid

Question 18

what does mRNA determine

Answer 18

the sequence of amino acids in the protein being synthesised

Question 19

where is tRNA found

Answer 19

cytoplasm

Question 20

what causes tRNA to fold into a clover leaf shape

Answer 20

complimentary base pairings within tRNA molecule

Question 21

what two distinct regions does tRNA folding create

Answer 21

1. exposed triplet anticodon site
2. attachment site for a specific amino acid

Question 22

what does each tRNA molecule have

Answer 22

an attachment site which carries a specific amino acid to the ribosome for the translation of the genetic code.

Question 23

what is the exposed triplet of bases on a tRNA molecule called

Answer 23

anticodon

Question 24

what does an rRNA molecule do

Answer 24

combine with proteins to form the structure of ribosomes

Question 25

what is a ribosome composed of

Answer 25

two sub units - one large and one small and is the site of protein synthesis

Question 26

where does transcription occur

Answer 26

nucleus

Question 27

why is mRNA required for transcription

Answer 27

to carry a copy of the DNA code from the nucleus to the ribosome

Question 28

what is the role of RNA polymerase in transcription

Answer 28

1. unwinds the DNA double helix and breaks hydrogen bonds between bases 2. synthesises the primary mRNA strand from free RNA nucleotides

Question 29

what is the first stage of transcription

Answer 29

RNA polymerase moves along the DNA molecule unwinding the double helix and breaking hydrogen bonds between bases of gene to be expressed

Question 30

what is the second stage of transcription

Answer 30

free RNA nucleotides align against exposed DNA bases of template strand. RNA polymerase can only add nucleotides to the 3' end

Question 31

what is stage 3 of transcription

Answer 31

complimentary base pairing ensures correct positioning of RNA nucleotides which are then joined by strong chemical bonds to form primary transcript

Question 32

what is stage 4 of transcription

Answer 32

weak hydrogen bonds are broken between DNA and RNA nucleotides allowing mRNA to break away from DNA template

Question 33

what is stage 5 of transcription

Answer 33

mRNA strand is then modified (RNA splicing) and can be transported out of nucleus to cytoplasm

Question 34

what is the last stage of transcription

Answer 34

weak hydrogen bonds reunite the two original DNA strands which twist again to form a double helix

Question 35

what happens during RNA splicing

Answer 35

introns are removed and exons are retained

Question 36

what is an intron

Answer 36

non coding regions of a gene

Question 37

what is an exon

Answer 37

coding region of a gene which is expressed

Question 38

what are introns used for

Answer 38

regulate transcription and can be transcribed into RNA

Question 39

what is the transcript known as before and after splicing

Answer 39

before - primary mRNA after - mature mRNA

Question 40

what happens to mRNA after splicing

Answer 40

leaves nucleus and enters cytoplasm to join with ribosome

Question 41

what happens to the order of exons during splicing

Answer 41

unchanged

Question 42

what does alternative RNA splicing result in

Answer 42

different proteins being expressed from one gene

Question 43

what does different mature mRNA molecules being produced from the same primary transcript depend on

Answer 43

which primary mRNA segments are treated as exons and which are introns

Question 44

what allows translation to begin

Answer 44

the mature mRNA transcript leaves the nucleus via a nuclear pore and attaches to a ribosome

Question 45

what does translation begin with

Answer 45

a start codon

Question 46

what is stage 1 of translation

Answer 46

each tRNA molecule attaches to a specific amino acid in cytoplasm which it transports to the mRNA at the ribosome

Question 47

what is stage 2 of translation

Answer 47

each tRNA molecule aligns with the mRNA according to their anticodon which is complimentary to the mRNA codon

Question 48

what is stage 3 of translation

Answer 48

once 2 amino acids have lined up, a peptide bond forms between them

Question 49

what is stage 3 of translation

Answer 49

the first tRNA molecule detaches from the mRNA and is now free to collect another amino acid from the cytoplasm

Question 50

what is stage 4 of translation

Answer 50

ribosome moves along mRNA strand and the process continues until a poly peptide chain is formed

Question 51

what is stage 5 of translation

Answer 51

the polypeptide chain then folds to form a protein which is held in a 3D shape by hydrogen bonds and other linkages

Question 52

what does translation end with

Answer 52

a stop codon

Question 53

where is the primary transcript of mRNA formed

Answer 53

nucleus

Question 54

where is primary transcript of mRNA modified

Answer 54

nucleus

Question 55

where are amino acids collected by tRNA

Answer 55

cytoplasm

Question 56

where are codon-anticodon links formed

Answer 56

ribosome