W8.1_DNA

Question 1

Define DNA and describe the structure of a nucleotide. Explain how bases are paired up in DNA and are classified.

Answer 1

• Made of nucleotides in a double helix structure, with phosphate and sugar as backbone
• Nucleotide: phosphate group + pentose sugar + nitrogenous base
• Bases: Adenine <-base pair-> Thymine (2 H-bonds)
• Cytosine <-base pair-> Guanine (3 H-bonds)
• Held by complementary base-pairing (%A=%T & %C=%G), C<->G are more strongly bonded
• A&G: purines
• T&C&U(RNA): pyrimidines

Question 2

Describe the similarity in genome in all specialised cells. What do cells do right before cell division?

Answer 2

• All specialised cells: same genome but different genes are expressed (≈99% are shut down)
• Right before cell division: DNA wraps around histone proteins, becomes spooled -> condenses into chromosomes

Question 3

Contrast genome and gene. How are bases arranged?

Answer 3

• Genome: everyone is different -> unique genome = genotype
• All visible/non-visible traits = phenotype (coded by genotype)
• Genotype underpins our predisposition to disease and drug response
• Gene: section of DNA that codes for proteins (unique sequences of bases will code for production of unique proteins)
• Combination of proteins -> unique phenotype
• Bases: arranged in triplets (codons) -> code for specific amino acid

Question 4

Define DNA replication. Describe the process of DNA replication. How can some anti-cancer drugs interfere with DNA bases pairing?

Answer 4

• DNA replication: separating and copying two strands of DNA
• Specialist proteins separate two strands of DNA -> another specialist protein brings correct new base with existing base (through complementary base pairing) ∴ Each new DNA: one old strand + one new strand
• Some functions of anti-cancer drugs: form covalent bonds with bases (ex. cisplatin <-> guanine), act as intercalating agent (ex. doxorubicin)

Question 5

Describe the cell cycle in detail. (G1, S, G2, PMAT, G0)

Answer 5

• G1 (Gap phase 1): cell grow in size, synthesise cell organelles & macromolecules, accumulate sufficient energy
• S (Synthesis phase): DNA replication, duplicates centrosome, gives rise to spindle fibres
• G2 (Gap phase 2): cell keeps growing and until all organelles have duplicated
• M (Mitotic phase)
• Prophase (chromosomes condense, nuclear envelope disintegrates, centrioles move to opposite poles to form spindle fibres)
• Metaphase (chromosomes line up along the middle of cell)
• Anaphase (centrosome splits, chromatids are pulled to opposite poles)
• Telophase (two groups of chromosomes decondense, nuclear envelopes reform to form nuclei)
• Cytokinesis (cytoplasm divides)
• Some end in G0 phase (resting phase), especially for cells that never/seldom divide (ex. nerve cells, cardiac cells)