Nucleic acids (2)

Question 1

Draw the structure of a nucleotide.

Answer 1

look at diagram in notes

Question 2

What is the role of DNA in living cells?

Answer 2

• base sequence of gene codes for functional RNA + amino acid sequence of polypeptides
• genetic information determines inherited characteristics which influences structure + function of organisms

Question 3

What are the 3 types of RNA?

Answer 3

mRNA
rRNA
tRNA

Question 4

What is the role of mRNA in living cells?

Answer 4

complementary sequence to 1 gene from DNA with introns spliced out so codons can be translated into a polypeptide by ribosomes

Question 5

What is meant by an intron?

Answer 5

non-coding region

Question 6

What is the role of rRNA in living cells?

Answer 6

component of ribosomes

Question 7

What is the role of tRNA in living cells?

Answer 7

supplies complementary amino acids to mRNA codons during translation

Question 8

How do polynucleotides form?

Answer 8

condensation reactions between nucleotides form strong phosphodiester bonds

Question 9

What is the structure of DNA?

Answer 9

• double helix of 2 polynucleotide strands (deoxyribose)
• H-bonds between complementary purine and pyrimidine base pairs on opposite strands

Question 10

What are the 4 bases in DNA?

Answer 10

adenine + thymine
guanine + cytosine

Question 11

How many bonds are between each of the base pairs in DNA?

Answer 11

A + T have 2 H-bonds between
G + C have 3 H-bonds between

Question 12

What type of base are A and G?

Answer 12

2-ring purine bases

Question 13

What type of base are T, C and U?

Answer 13

1-ring pyrimidine bases

Question 14

Which bases are 2-ring purine?

Answer 14

A and G

Question 15

Which bases are 1-ring pyrimidine?

Answer 15

T, C and U

Question 16

What are the 4 bases in RNA?

Answer 16

adenine + uracil
guanine + cytosine

Question 17

Rank DNA, mRNA and tRNA from shortest to longest.

Answer 17

tRNA - mRNA - DNA

Question 18

What are 5 structures of DNA?

Answer 18

• sugar-phosphate backbone
• base sequence of triplets
• double-stranded
• complementary base pairing
• many H-bonds

Question 19

What are 3 structures of mRNA?

3

Answer 19

• contains uracil not thymine
• single-stranded and linear
• codon sequence is complementary to exons of 1 gene from 1 DNA strand

Question 20

What is the structure of tRNA?

Answer 20

• single strand of about 80 nucleotides
• folded into clover shape
• anticodon on 1 end and amino acid binding site on the other

Question 21

What does the anticodon on tRNA do?

Answer 21

binds to complementary mRNA codon

Question 22

What did some scientists initially doubt and why?

Answer 22

Initially doubted DNA carried the genetic code as it’s a chemically simple molecule with few components

Question 23

What are 2 reasons why DNA replication is called semi-conservative?

Answer 23

• strands from original DNA molecule act as a template
• new DNA molecule contains 1 old strand and 1 new strand

Question 24

What are the 5 steps of semi-conservative DNA replication?

Answer 24

1) DNA helicase breaks H-bonds between base pairs
2) each strands acts as a template
3) free nucleotides from nuclear sap attach to exposed bases by complementary base pairing
4) DNA polymerase catalyses condensation reactions that join adjacent nucleotides on new strand
5) H-bonds reform

Question 25

What were the 4 steps of the Meselson-Stahl experiment?

Answer 25

1) bacteria were grown in a medium containing heavy isotope 15N for many generations 2) some bacteria were moved to a medium containing light isotope 14N 3) samples were extracted after 1 and 2 cycles of DNA replication 4) centrifugation formed a pellet - heavier DNA (bases made from 15N) settled closer to bottom of tube

Question 26

What was the name of the experiment using 14N and 15N?

Answer 26

Meselson-Stahl experiment

Question 27

How does having a sugar-phosphate backbone and many H-bonds relate to DNA's function?

Answer 27

provides stability

Question 28

How does having a base sequence of triplets relate to DNA's function?

Answer 28

code for amino acids

Question 29

How does being double-stranded relate to DNA's function?

Answer 29

for semi-conservative replication

Question 30

How does having complementary base pairing relate to DNA's function?

Answer 30

for accurate replication

Question 31

How does having H-bonds relate to DNA's function?

Answer 31

they are weak so break so strands separate for replication

Question 32

How does containing uracil not thymine relate to mRNA's function?

Answer 32

breaks down quickly so no excess polypeptide forms

Question 33

How does being single-stranded and linear relate to mRNA's function?

Answer 33

so ribosome can move along strand and tRNA can bind to exposed bases

Question 34

How does having a codon sequence complementary to exons of 1 gene from 1 DNA strand relate to mRNA's function?

Answer 34

so can be translated into specific polypeptide by ribosomes