Protein synthesis

Question 1

structure of mRNA

Answer 1

single stranded, complementary to a gene in the DNA molecule

Question 2

structure of tRNA

Answer 2

• single stranded, but the structure folds back on itself so some of the tRNA bases pair up with others from the same strand.
• it is small (80 nucelotides), folded into clover leaf shape. one end of the tRNA molecule extends beyond the rest of the molecule, this attaches to the amino acid, at the opposite end there are 3 unpaired bases, this creates the anticodon.

Question 3

describe the structure of DNA

Answer 3

• double stranded
• longer strand
• linear
• has hydrogen bonds

Question 4

describe the structure of mRNA

Answer 4

• single stranded
• short strand
• linear
• no hydrogen bonds

Question 5

describe the structure of tRNA

Answer 5

• single stranded (but folded back on itself)
• shorter stand (than DNA and mRNA)
• clover leaf shape
• hydrogen bonds (does complementary base pairing)
• amino acid binding site

Question 6

define the genome

Answer 6

the complete set of genes in a cell

Question 7

define the proteome

Answer 7

the full range of proteins that a cell is able to produce

Question 8

what are the three bases in DNA that code for a specific amino acid called?

Answer 8

triplet

Question 9

what are the three bases in mRNA that code for a specific amino acid called?

Answer 9

codon

Question 10

what are the three bases in tRNA that code for a specific amino acid called?

Answer 10

anticodon

Question 11

what two processes does protein synthesis involve

Answer 11

translation and transcription

Question 12

where does transcription take place?

Answer 12

in the nucleus (except in prokaryotes, then it takes place in the cytoplasm)

Question 13

describe the 5 stages of transcription

Answer 13

1. the DNA strands separate over the length of the gene to be expressed, DNA helicase does this by breaking the hydrogen bonds.
2. one of the strands acts as the template strand and is used to make a complementary mRNA strand. Free RNA nucleotides bases pair with their complementary DNA bases via hydrogen bonds.
3. the enzyme RNA polymerase moves along the template strand and joins the nucelotides together via phosphodiester bonds. it is now a pre-mRNA strand which includes both introns and exons.
4. splicing occurs removing all introns. it is now an mRNA strand
5. the mRNA strand diffuses out of the nuclear pore.

Question 14

what are the two differences between protein synthesis in prokaryotes and eukaryotes?

Answer 14

1. because prokaryotic DNA does not have any introns splicing doesn’t have to occur, and there is no pre-mRNA strand.
2. because prokaryotic cells do not have a nucleus, protein synthesis takes place in the cytoplasm.

Question 15

describe the 6 stages of translation

Answer 15

1. mRNA attaches to a ribosome via the start codon
2. a tRNA molecule with a complementary anticodon to the codon on the mRNA bonds via hydrogen bonds and brings the specific amino acid
3. another tRNA molecule with a complementary anticodon brings its specific amino acid
4. the two amino acids join via a peptide bond (which requires ATP)
5. the ribosome moves along the mRNA strand (max two tRNA fit) a tRNA molecule brings its specific amino acid, which binds onto the previous amino acid (peptide) forming a chain
6. this process continues until a stop codon is reached at which point the ribosome, mRNA and last tRNA molecule will separate. the polypeptide chain is complete.

Question 16

what happens to a tRNA molecule once it leaves the ribosome?

Answer 16

it finds another one of its specific amino acid in the cytoplasm

Question 17

what happens to the polypeptide chain after translation?

Answer 17

the polypeptide chain folds up (secondary structure => tertiary structure => maybe quarternary)