Nucleotide and Nuclei acids

Question 1

What are nucleotides composed of?

Answer 1

A phosphate group, a pentose sugar, and a nitrogenous base.

Question 2

What are the two types of nucleic acids?

Answer 2

DNA (deoxyribonucleic acid) and RNA (ribonucleic acid).

Question 3

How do DNA and RNA differ?

Answer 3

DNA is double-stranded with deoxyribose and thymine, while RNA is single-stranded with ribose and uracil.

Question 4

What are the two types of nitrogenous bases?

Answer 4

Purines: Adenine (A) and Guanine (G) (double-ringed).

Pyrimidines: Cytosine (C), Thymine (T), and Uracil (U) (single-ringed).

Question 5

What type of bond forms between nucleotides?

Answer 5

Phosphodiester bonds, formed in condensation reactions.

Question 6

What is the structure of DNA?

Answer 6

DNA is a double helix with two antiparallel polynucleotide strands, stabilized by hydrogen bonds between complementary bases.

Question 6

What is complementary base pairing?

Answer 6

Adenine (A) pairs with Thymine (T) (or Uracil (U) in RNA), and Cytosine (C) pairs with Guanine (G) via hydrogen bonds.

Question 7

How many hydrogen bonds form between base pairs?

Answer 7

A-T (or A-U in RNA) = 2 hydrogen bonds

C-G = 3 hydrogen bonds

purines have single rings, pyramdine have double rings

Question 8

How is DNA suited to its function?

Answer 8

Stable: Hydrogen bonds and double-helix structure protect genetic information.

Compact: Can store large amounts of information.
Replication:

Complementary base pairing enables accurate copying.

Mutation Possibility: Allows evolution while maintaining stability.

Question 9

What is ATP (Adenosine Triphosphate)?

Answer 9

energy-carrying molecule

Question 10

What are the three types of RNA, and what are their functions?

Answer 10

mRNA (Messenger RNA): Carries genetic information from DNA to ribosomes for protein synthesis.

tRNA (Transfer RNA): Brings amino acids to ribosomes during translation.

rRNA (Ribosomal RNA): Forms part of ribosome structure and facilitates translation.

Question 11

How does ATP release energy?

Answer 11

Hydrolysis of the terminal phosphate group by ATP hydrolase releases energy, forming ADP and Pi (inorganic phosphate).

Question 11

What is the structure of ATP?

Answer 11

Composed of ribose, adenine, and three phosphate groups.

Question 12

How is ATP resynthesized?

Answer 12

By ATP synthase during respiration and photosynthesis through a condensation reaction.

Question 13

What is meant by semi-conservative replication?

Answer 13

Each new DNA molecule consists of one original strand and one newly synthesised strand.

Question 14

What are the steps of DNA replication?

Answer 14

DNA helicase unwinds the double helix and breaks hydrogen bonds.

Free nucleotides align with complementary bases.

DNA polymerase joins nucleotides with phosphodiester bonds.

Question 15

Why is DNA replication important?

Answer 15

Ensures genetic continuity.

Question 16

What is the role of DNA polymerase?

Answer 16

Catalyses the formation of phosphodiester bonds in the new DNA strand.

Question 17

What is the function of DNA helicase?

Answer 17

Unwinds the DNA double helix and breaks hydrogen bonds between complementary bases.

Question 18

What are Okazaki fragments?

Answer 18

Short DNA fragments synthesized on the lagging strand during replication.

Question 19

What is the genetic code?

Answer 19

The sequence of nucleotide bases in DNA that codes for amino acids in proteins.

Question 20

What are the features of the genetic code?

Answer 20

Triplet: Each amino acid is coded by three bases (a codon).

Degenerate: More than one codon can code for the same amino acid.

Universal: The same codons code for the same amino acids in all organisms.

Non-overlapping: Each triplet is read separately.

Question 21

What is a codon?

Answer 21

A sequence of three nucleotides that codes for a specific amino acid.

Question 22

What are start and stop codons?

Answer 22

Start codon: AUG (Methionine) initiates protein synthesis.
Stop codons: UAA, UAG, UGA signal the end of translation.

Question 23

What is a mutation?

Answer 23

A change in the base sequence of DNA.

Question 24

What are types of mutations?

Answer 24

Substitution: One base is replaced by another. Insertion: An extra base is added. Deletion: A base is removed.

Question 25

What is a frameshift mutation?

Answer 25

Insertions or deletions shift the reading frame, altering all downstream codons.

Question 26

What is the impact of mutations on protein function?

Answer 26

Mutations can lead to: Silent mutation: No effect (same amino acid). Missense mutation: Different amino acid (may alter function). Nonsense mutation: Stop codon introduced, leading to a non-functional protein.

Question 27

What are the two stages of protein synthesis?

Answer 27

Transcription: DNA → mRNA (in the nucleus). Translation: mRNA → protein (at the ribosome).

Question 28

What happens during transcription?

Answer 28

• DNA helicase breaks hydrogen bonds, unwinding the double helix. • One DNA strand acts as a template (antisense strand, 3’ → 5’). • RNA polymerase binds at the start of the gene and moves along, assembling a complementary pre-mRNA strand (5’ → 3’) using free RNA nucleotides (Uracil replaces Thymine). • Transcription stops at a terminator sequence, and pre-mRNA detaches. • Splicing removes introns, forming mature mRNA, which exits via a nuclear pore.

Question 29

What happens during transcription?

Answer 29

mRNA binds to a ribosome. tRNA with complementary anticodon carries an amino acid to the ribosome. Ribosome catalyzes peptide bond formation between amino acids. Process continues until a stop codon is reached.

Question 30

What is the role of tRNA in translation?

Answer 30

tRNA molecules transport specific amino acids to the ribosome based on anticodon-mRNA pairing.

Question 31

How is the polypeptide chain modified after translation?

Answer 31

It undergoes folding and chemical modifications in the Golgi apparatus.

Question 32

Compare transcription and translation (6 marks)

Answer 32

**Transcription** • Occurs in the nucleus (eukaryotes). • DNA helicase unwinds DNA, breaking hydrogen bonds. • RNA polymerase binds at the start of the gene and synthesises pre-mRNA using the antisense strand as a template. • Complementary base pairing occurs (Uracil replaces Thymine). • Pre-mRNA is spliced to remove introns, forming mature mRNA. • mRNA exits the nucleus via a nuclear pore. **Translation** • Occurs in the ribosome (cytoplasm or RER). • mRNA binds to ribosome, where each codon is read. • tRNA brings specific amino acids, using anticodon-codon complementary base pairing. • Ribosome catalyses peptide bond formation, forming a polypeptide. • Stops at a stop codon, releasing the completed protein.