Nucleic Acids

Question 1

How is the structure of DNA adapted to its function ?

8

Answer 1

• double stranded =stable
• bases are on inside = protected , code is maintained
• molecules are long = store a lot of genetic information
• Hydrogen bonds = break for transcription and maintain shape

Question 2

When does DNA replication occur ?

Answer 2

Interphase -

S phase

Question 3

Outline DNA replication
(5)
5- main points
3- enzymes

Answer 3

1- unwinds (Gryase)
2- Unzips (Helicase)
3-free phosphorylated nucleotide in nucleoplasm bind to exposed bases
4- Bonding /joining of bases ( DNA Polymerase ) Semi conservative
5-Hydrolysis removes extra phosphate groups

Question 4

Purines ?

Structure / 2bases

Answer 4

Have 2 rings ( hexose and pentose )

• Adenine
• Guanine

Question 5

Pyrimidine ?

Structure / bases

Answer 5

1 hexose ring

• Cytosine
• Thymine / Uracil

Question 6

How is the lagging strand synthesised in DNA replication?

Answer 6

Discontinuously

- enzyme Ligase joins it up later

Question 7

What enzymes are involved in DNA replication and what is there function ?
6 marks

Answer 7

1. Gryase - Catalyses unwinding of DNA
2. Helicase - catalyses the breaking of hydrogen bonds between bases
3. DNA Polymerase- cataclysms he addition of new nucleotides to both old strands

Question 8

Why is DNA replication semi conservative?

Answer 8

• 2 new molecules contain an old strand and new strand

Question 9

What organelles are involved in protein synthesis ?

Answer 9

1- ribosome
2-nucleus & and nucleolus
3-endoplasmic reticulum
4-mitochondria

Question 10

What is the function of a ribosome ?

Answer 10

Catalyst - allows polypeptide to form by bringing amino acids close together

Question 11

Where is MRNA made ?

Answer 11

Nucleus

Question 12

Where are ribosomes made / how do they pass out ?

Answer 12

• made in nucleolus into 2 smaller subunits
• pass Out separately in 2 subunits
• Mg later bonds them together

Question 13

Why are ribosomes thought of as catalysts ?

Answer 13

They are unchanged at the end of reaction

They allow amino acids close together to form polypeptides

Question 14

Outline transcription ?
(4)
-strands

Answer 14

1- DNA unwinds :
There is a coding strand and a non coding strand
2- free nucleotides bond to non coding strand .
3 - template is made
4- template is same to Coding strand
This template is MRNA
- Thymine is replaced with Uracil

Question 15

Outline translation

5

Answer 15

1-mRNA codons go to ribosome
2-TRNA brings anticodon / amino acids
3-Anticodons pair up with bases in mRNA temporarily
4- Amino acids are meanwhile forming the primary structure - joint by peptide bonds
5-competed protein folds up appropriately

Question 16

What is a sequence of 3 bases Called in :
1- DNA
2-mRNA
3-tRNA

Answer 16

1- bass triplet
2-Codon
3-Anticodon

Question 17

What’s transcription ?

Answer 17

Transcription is the process of making MRNA from DNA

Question 18

What is translation ?

Answer 18

Translation is :

• formation of protein
• by assembling amino acids into particular sequence according to coded instructions given by mRNA from nucleus .
• at ribosomes

Question 19

Function of mRNA

Answer 19

-carries instruction / template to the ribosomes for protein synthesis

Question 20

Function of TRNA ?

Answer 20

tRNA brings anticodons to ribosome and hence amino acids forming the primary structure of a protein and polypeptide chain !