Topic 4A: DNA, RNA and protein synthesis

Question 1

how does DNA exist as in a eukaryotic cell?

Answer 1

• found in the nucleus
• linear DNA
• long DNA molecule so is wound around proteins known as histones (help support)
• DNA coiled up compactly into chromosomes

Question 2

what type of DNA does chloroplast and mitochondria have?

Answer 2

• circular and shorter
• not associated with histones

Question 3

how does DNA exist as in a prokaryotic cell?

Answer 3

• DNA molecule shorter and circular
• isn’t wound around histones
• carried in a chromosome
• it condenses via super-coiling

Question 4

what is a gene?

Answer 4

a sequence of DNA bases that code for either a polypeptide or functional RNA

Question 5

what does the sequence of amino acids determine?

Answer 5

the polypeptide that forms the primary structure of a protein

Question 6

what is a triplet/codon?

Answer 6

a sequence of three bases in a gene that codes for an amino acid

Question 7

what is functional RNA?

Answer 7

genes that don’t code for a polypeptide
- perform special tasks during photosynthesis

Question 8

what is a genome?

Answer 8

complete set of genes in a cell

Question 9

what is a proteome?

Answer 9

full range of proteins a cell can produce

Question 10

what are introns?

Answer 10

parts of gene that do not code for amino acids
(prokaryotic cells do not have introns)

Question 11

what are extons?

Answer 11

parts of gene that do code for amino acid

Question 12

what is non-coding multiple repeats?

Answer 12

regions of DNA sequences that multiply repeat

Question 13

what is an allele?

Answer 13

a different form of the same gene
(they are slightly different so code for slightly different versions of the same polypeptide)

Question 14

what is a homologous pair?

Answer 14

chromosomes of similar size and same coding for gene (although could be a different allele) are matched

Question 15

what is a locus?

Answer 15

a fixed position on a homologous chromosome where alleles code for the same characteristic

Question 16

what is protein synthesis?

Answer 16

production of proteins from information inside cell’s DNA

Question 17

what happens in protein synthesis?

Answer 17

transcription-
where DNA code is copied into mRNA

translation-
mRNA joins to ribosomes and code then synthesizes a protein

Question 18

what is RNA?

Answer 18

a single polynucleotide strand containing uracil (U) instead of thymine (T)
- it is always paired with adenine (A)

Question 19

what is the structure of mRNA?

Answer 19

• made during transcription
• carries genetic code from DNA to ribosome to make protein
• single polynucleotide strand
• group of three adjacent bases called codons/triplets

Question 20

what is the structure of tRNA?

Answer 20

• carries amino acids to ribosomes to make proteins
• single polynucleotide strand folded into a clover shape
• hydrogen bonds between specific base pairs hold this shape
• a specific sequence of 3 bases at one end called an anticodon
• amino acid binding site on the other end

Question 21

How does translation occur?

Answer 21

‘the production of mRNA from DNA’
1) RNA polymerase attaches to double helix at start of gene
2) hydrogen bonds break between two strands
3) molecule uncoils exposing some bases
4) one strand is used as a template to make mRNA copy

1) RNA polymerase lines up free RNA nucleotides along template
2) specific complementary base pairings meaning mRNA is a complementary copy
3) complementary bases are joined by RNA polymerase to produce mRNA

1) RNA polymerase moves along DNA separating and assembling
2) hydrogen bonds reform after enzyme has passed forming its original double helix

1) RNA polymerase reaches a stop signal
and MRNA detaches from DNA
2) moves out of nucleus through nuclear pore and attaches to ribosome in the cytoplasm

Question 22

what is splicing?

Answer 22

introns and exons are copied into mRNA known as pre-MRNA
- introns are removed and exons are joined together

Question 23

what is translation?

Answer 23

‘amino acids join to make a polypeptide chain following codon sequence from mRNA’

1) mRNA attaches itself to a ribosome and tRNA carries an amino acid towards it (energy is needed to form the bond between the two)

2) tRNA molecule with anticodon complementary to codon on the mRNA attaches

3) a second tRNA molecule attaches in the same way

4) two amino acids attached to tRNA are joined by a polypeptide bond

5) first tRNA molecule moves away leaving amino acid behind

6) a third tRNA molecule binds to next codon on mRNA. It’s amino acid binds to the first two producing a polypeptide chain until there is a stop signal

7) polypeptide chain then moves away from ribosome and translation is complete

Question 24

what is the genetic code?

Answer 24

a sequence of base triplets in mRNA which code for a specific amino acid

Question 25

what does non-overlapping mean?

Answer 25

each base triplet is read in sequence, separate from triplet before and after it

Question 26

what is degenerate?

Answer 26

there are more possible combinations of triplets than there are amino acids (only 20) - this means an amino acid can be coded by more than one triplet (not all code for an amino acid tho)

Question 27

what does it mean by universal?

Answer 27

the same specific base triplets that code for the same amino acids in all living things