Topic 5 - DNA and protein synthesis

Question 1

what does mRNA stand for

Answer 1

messenger RNA

Question 2

what is mRNA

Answer 2

the RNA formed in the nucleus that carries the genetic code out into the cytoplasm

Question 3

what is an antisense strand

Answer 3

the DNA strand that codes for proteins

Question 4

what is RNA polymerase

Answer 4

the enzyme that polymerises nucleotide units to form RNA in a sequence determined by the antisense strand of DNA

Question 5

what does tRNA stand for

Answer 5

Transfer RNA

Question 6

what is tRNA

Answer 6

small units of RNA that pick up particular amino acids from the cytoplasm and transport them to the surface of the ribosome to align with the mRNA

Question 7

what is an anticodon

Answer 7

a sequence of 3 bases on tRNA that are complementary of the ribosomes

Question 8

what does rRNA stand for

Answer 8

ribosomal RNA

Question 9

what is rRNA

Answer 9

RNA that makes up about 50% of the structure of the ribosome

Question 10

what are polysomes

Answer 10

groups of ribosomes, joined by a thread of mRNA, that can produce large quantities of a particular protein

Question 11

what is a sense strand

Answer 11

has the same base sequence as the mRNA transcribed from the antisense strand

Question 12

what are 3 differences between RNA and DNA

Answer 12

• RNA contains ribose, and DNA contains deoxyribose
• RNA has the base uracil, and DNA has the base thymine
• RNA consists of a single helix, and DNA consists of a double helix

Question 13

what are 2 similarities between RNA and DNA

Answer 13

• both don’t form large complex molecules
• the sequence of bases on the RNA, relates the a small part of the sequence of bases of the DNA

Question 14

what are 3 functions of RNA in protein synthesis

Answer 14

• it carries the instructions for a polypeptide from the DNA in the nucleus to the ribosomes
• It picks up specific amino acids from the protoplasm and carries them to the surface of the ribosomes
• it makes up the bulk of the ribosomes

Question 15

what are the 4 stages of DNA replication

Answer 15

1. DNA unwinds
2. single strand acts as a template
3. sugar-phosphate backbone is formed
4. DNA rewinds

Question 16

explain in step 1 of DNA replication, how the DNA unwinds

Answer 16

the hydrogen bonds holding the bases together beak, catalysed by DNA helicase. When the 2 halves of the molecule separate, the DNA bases are exposed

Question 17

explain in step 2 of DNA replication, how the single strands act as a template

Answer 17

Each strand of DNA acts as a template for the new strands. Free nucleotides enter the nucleus from the cytoplasm and assemble on the template DNA according to the law of base pairing. The nucleotides are held in place by hydrogen bonds

Question 18

explain in step 3 of DNA replication, how the sugar-phosphate backbone is formed

Answer 18

Condensation reactions link the new nucleotides together, to form the sugar-phosphate backbone, which is catalysed by DNA polymerase. This enzyme also ‘proofreads’ each new strand, correcting any mistakes made

Question 19

where do phosphodiester bonds form

Answer 19

between each nucleotide

Question 20

where do hydrogen bonds form

Answer 20

between each base

Question 21

what does DNA ligase catalyse

Answer 21

the joining of different segments

Question 22

explain in step 4 of DNA replication, how the DNA rewinds

Answer 22

each daughter DNA molecule rewinds into a double helix

Question 23

what are the 4 enzymes that catalyse in the process of DNA replication

Answer 23

• helicase
• polymerase
• DNA polymerase
• ligase