2.3.3 how DNA codes for polypeptides

Question 1

gene

Answer 1

length of DNA that codes for a polypeptide/for length of RNA that’s involved in regulating gene expression

Question 2

polypeptide

Answer 2

polymer made of amino acid units joined together by peptide bonds

Question 3

protein

Answer 3

large polypeptide of 100+ amino acids

Question 4

transcription

Answer 4

process of making messenger RNA from DNA template

Question 5

translation

Answer 5

formation of a protein (at ribosomes) by assembling amino acids into particular sequence according to coded instructions carried from DNA to ribosome by mRNA

Question 6

how is RNA structurally different from DNA

Answer 6

• sugar molecule in nucleotide = ribose
• nitrogenous base uracil replaces thymine
• polynucleotide chain = usually single-stranded
• polynucleotide chain is shorter
• 3 forms of RNA: messenger RNA, transfer RNA & ribosomal RNA

Question 7

is uracil a pyrimidine or purine

Answer 7

pyrimidine

Question 8

what is present within each gene which determines the amino acids sequence/primary structure of a polypeptide

Answer 8

sequence of DNA base triplets

Question 9

where are genes

Answer 9

inside cell nucleus

Question 10

why does a copy of each gene have to be transcribed into a length of mRNA

Answer 10

instructions inside genes (on chromosomes) cannot pass out of nucleus

Question 11

what is the sequence of base triplets called in mRNA

Answer 11

codons

Question 12

nature of genetic code

Answer 12

• universal = in almost all living organisms, the same triplet of DNA bases codes for same amino acid
• degenerate = for all (except 2) amino acids, there is more than 1 base triplet
• non-overlapping = read starting from fixed point in groups of 3 bases

Question 13

what’s transcription

Answer 13

transcription of a gene into length of mRNA

Question 14

describe process of transcription

Answer 14

1. gene unwinds/unzips
2. h bonds between complementary nucleotide bases break
3. RNA polymerase catalyses formation of temporary h bonds between RNA nucleotides & complementary unpaired bases (A+T, C+G, G+C, U+A) = template strand
4. length of RNA complementary to template strand of gene produced (copy of other DNA strand) = coding strand
5. mRNA passes out of nucleus, through nuclear envelope & attaches to ribosome

Question 15

where are ribosomes made

Answer 15

nucleolus in 2 smaller subunits

Question 16

what helps bind 2 subunits to form ribosomes

Answer 16

magnesium ions

Question 17

what are ribosomes made of

Answer 17

ribosomal RNA & protein (roughly equal parts)

Question 18

where are transfer RNA molecules made

Answer 18

nucleolus

Question 19

structure of transfer RNA

Answer 19

• single-stranded polynucleotides
• can twist into hairpin shape
• 1 end = trio of nucleotide bases which recognise/attach to specific amino acid
• loop of hairpin = triplet of bases (anticodon) –> complementary to specific codon of bases on mRNA

Question 20

name of triplet of bases in tRNA

Answer 20

anticodon

Question 21

what do ribosomes catalyse

Answer 21

synthesis of polypeptides

Question 22

process of translation

Answer 22

1. tRNA molecules bring amino acids & find place when anticodon binds by temporary h bonds to complementary codon on mRNA
2. ribosome moves along mRNA - reads code & when 2 amino acids adjacent to each other a peptide bonds forms between
3. energy (ATP) needed for polypeptide synthesis
4. amino acid sequence for polypeptide thus, determined by sequence of triplets of nucleotide bases of DNA
5. after polypeptide assembled, mRNA breaks down –> component molecules can be recycled into new lengths of mRNA (w/ diff. codon sequences)
6. newly synthesised polypeptide helped (chaperone proteins) to fold into 3D shape/tertiary structure to carry out function