Unit 4,protein synthesis

Question 1

characteristics of mRNA

Answer 1

-made during transcription
-carries genetic code from DNA to ribosome eventually making a protein, because dna is to large to move to dna
-they are a single polynucleotide strand

Question 2

characteristics of tRNA

Answer 2

-involved in translation
-carries the amino acids that are used to make proteins to the ribosomes
-single polynucleotide strand that is folded into a clover shape, held in shape by hydrogen bonds
-at one end there is a specific anticodon that binds to mRNA
-at the other end has an amino acid binding site

Question 3

what is the 1st stage of the transcription process?

Answer 3

RNA polymerase attaches to DNA
-transcription starts when RNA polymerase attaches at the start of a gene. when the DNA is unwound by the helicase the remainder strand of the DNA is used as a template to make a mRNA copy
- helicase breaks hydrogen bonds

Question 4

what is the 2nd stage of the transcription process?

Answer 4

Complementary mRNA is formed
-RNA polymerase lines up and joins complementary bases to form mRNA for a complementary copy

Question 5

what is the 3rd stage of the transcription process?

Answer 5

RNA polymerase moves down DNA strand
-RNA polymerase forms hydrogen bonds as the double helix reforms

Question 6

what is the 4th stage of the transcription process?

Answer 6

RNA polymerase reaches stop signal
- meets a particular sequence called a stop signal, so it stops making mRNA and detaches from the DNA
-in eukaryotes it moves out of the nucleus through nuclear pores and attaches to ribosomes in the cytoplasm

Question 7

what happens in editing of mRNA in eukaryotes?

Answer 7

-introns and exons that are copied into mRNA are called pre-mRNA
-splicing then occurs

Question 8

what is splicing?

Answer 8

-introns are removed and exons are joined together forming an mRNA strand, which leaves the nucleus for translation, introns removed by splicesome
- exons can re-join together in a variety of combinations, so multiple proteins are made

Question 9

what happens in the editing of mRNA in prokaryotes?

Answer 9

there are no introns in prokaryotes DNA, so mRNA is made directly from the DNA

Question 10

what happens if a mutation occurs in editing of mRNA that alters pre-mRNA?

Answer 10

can lead to non functional polypeptides, for example Alzheimer’s

Question 11

what are exons?

Answer 11

regions which code for protein

Question 12

what are introns?

Answer 12

regions which do NOT code for proteins

Question 13

Where does translation take place?

Answer 13

In the ribosome

Question 14

What is a proteome?

Answer 14

Entire complement of proteins that can be expressed from genes

Question 15

What is the first stage of translation?

Answer 15

The mRNA attaches itself to a ribosome and tRNA molecules carry amino acids to it. ATP provides energy for this bond.

Question 16

What is the second stage of translation?

Answer 16

A tRNA molecule that’s carrying an amino acid that has a complementary anticodon to the first codon of the mRNA attaches together. A second tRNA molecule repeats this. Catalysed by an enzyme and ATP

Question 17

What is the third stage of translation?

Answer 17

The two amino acids that are attached to the tRNA are joined by a peptide bond. The first tRNA moves away and leaves the amino acid behind.

Question 18

What is the fourth stage of translation?

Answer 18

The third tRNA molecule binds to the next codon on the mRNA, they are complementary. The amino acid joins to the previous two by a peptide bond. The second tRNA molecule moves away

Question 19

What is the fifth stage of translation?

Answer 19

The process continues for a formation of amino acids in a chain, until the stop signal is reached. The polypeptide chain moves away from ribosome.

Question 20

What amino acid always is involved in the first stage?

Answer 20

Methionine

Question 21

What does degenerate mean?

Answer 21

Each amino acid could be coded for more than one amino acid ( the triplet code)