Nucleotides and Nucleic Acids

Question 1

Nucleotides

Answer 1

Nucleotides consist of pentose which is a 5 carbon sugar, a nitrogen containing organic base and a phosphate group

DNA Nucleotides
- Deoxyribose, a phosphate group and an Organic base (adenine, cytosine, guanine or thymine)

RNA Nucleotides
- Ribose, a phosphate group and an Organic base (adenine, cytosine, guanine or uracil)

• Nucleotides are joined together by phosphodiester bonds
• DNA molecules are a double helix made out of two polynucleotides joined together by hydrogen bonds
• RNA molecules are short, single chained molecule

Question 2

ATP (Adenosine triphosphate)

Answer 2

ATP (Adenosine triphosphate)
- made out of ribose, adenine, and 3 phosphate groups

• energy is released when ATP is hydrolysed to form ADP and a phosphate molecule. This reaction is catalysed by ATP hydrolase. The inorganic phosphate can be used to phosphorylate other compounds to make them more reactive
• Condensation of ADP and inorganic phosphate catalysed by ATP synthase
  produces ATP during photosynthesis and respiration.

Question 3

DNA Replication

Answer 3

DNA Replication (Semi-Conservative)
- Double Helix unwinds Hydrogen bonds between complementary bases break using DNA Helicase
- Both strands are used as templates, Complementary base paring occurs between the template strands and free nucleotides
- Adjacent nucleotides are joined by phosphodiester bonds formed in condensation reactions using DNA Polymerase

Question 4

Genetic Code

Answer 4

Genetic Code
- order of bases is called genetic code which consists of triplets of bases
- each triplet codes for a specific amino acid, known as a codon
- the non-coding sections of DNA are called introns and the coding regions are called exons.

• Genetic Code is non-overlapping, each triplet is only read once and triplets don’t share bases
• Genetic Code is degenerate, more than one triplet codes for the same amino acid, this reduces the effect of mutations (base deletion, insertion or substitution)
• Start and Stop codons start or stop protein synthesis

Question 5

Protein Synthesis

Answer 5

Transcription
- occurs in nucleus
- hydrogen bonds between the complementary bases break and the DNA uncoils
thus separating the two strands.
- One of the DNA strands is used as a template by RNA polymerase to make the
mRNA molecule. the DNA template is called the antisense strand
- Free nucleotides line up by complementary base pairing and adjacent nucleotides are joined by phosphodiester bonds made by RNA polymerase, forming a single stranded molecule of mRNA
- mRNA then moves out of the nucleus through a pore and attaches to a ribosome in the cytoplasm, this is where translation starts

Translation
- mRNA attaches to ribosome and transfer RNA collects amino acids from cytoplasm and carries them to the ribosome. tRNA is single stranded molecule with a binding site and triplets of bases at the other.
- tRNA attaches itself to mRNA by complementary base paring (2 tRNA attach to mRNA at the same time)
- the amino acids attached to two tRNA molecule join by a peptide bond and then the tRNA molecule detach from mRNA, leaving behind the amino acids
- This process is repeated leading to the formation of a polypeptide chain until a stop codon is reached on mRNA.