Heredity

Question 1

What are the structural properties of DNA?

Answer 1

• Carries instructions for all constructions - protein.
• Nucleotide: comprised of a phosphate molecule (backbone) connected to a pentose sugar - joint to a nitrogen base - forming the base pairs in the 5’ - 3’ (primer).

Question 2

What is the main function of DNA?

Answer 2

Create Proteins:

• control chemical reactions (enzymes).
• provide structure in bone, cartilage, skin.
• control movement across the cell membrane.
• hormone messengers.

Question 3

What are the stages of DNA Replication?

Answer 3

1) DNA helicase unzips the double helix (breaking the hydrogen bonds between nucleotides.
2) Single-stranded binding proteins stabilise DNA.
3) Leading Strand - synthesised continuously (5’-3’) direction by DNA Polymerase.
4) Lagging Strand - synthesised discontinuously (3’-5’) Primase synthesizes a short RNA primer, extended by DNA polymerase to form an Okazaki fragment.
5) After RNA Primer is replaced by DNA, DNA ligase joins Okazaki fragment to the growing strand.

Question 4

Cell Division:

What are the stages of Mitosis?

Answer 4

Mitosis forms two daughter cells (with identical sets of chromosomes) - All somatic cells are formed;

• Interphase: DNA replication occurs; cell grows larger.
• Prophase: Chromosomes condense (become visible) - nuclear membrane breaks down; centrioles migrate to poles of cell in spindle form.
• Metaphase: Condensed chromosomes move to the equator of cell - become attached to spindle forms.
• Anaphase: Sister chromatids separate and are dragged by spindle forms to opposite ends of the cell.
• Telophase: Two sets of chromosomes uncoil - nuclear membrane reforms and spindle fibres disappear.
• Cytokinesis: Division of cytoplasm - following the division of nucleus - creating two daughter (diploid) cells.

Question 5

What is the difference between eukaryote/prokaryote chromosomes?

Answer 5

• Eukaryote has membrane-bound organelles (nucleus) of with prokaryotes do not.
• Eukaryotes have histone proteins (coiled DNA) which link at the points called a centromere - whereas the DNA in prokaryotes are joint single-strands in the form of plasmids.

Question 6

Cell Divison:

What are the stages of Meiosis?

Answer 6

Forms four haploid gametes (sexually reproductive) cells (sperm and ovum) - each daughter cell has half the number of chromosomes (23 in humans):

• Metaphase 1: chromosomes line in homologous pairs in the middle of cell; exchange genetic material (increases variation).
• Anaphase 1: the chromosomes remain intact, and one whole chromosome is pulled form the pair to either poles of the cell.
• Anaphase 2: chromosomes/cells are pulled apart into sister chromatids to either end of the cell.
• Prophase: crossing over of genetic material before cells split forming gametes.

Question 7

What is Binary Fission?

Answer 7

A form of asexual reproduction (used by bacteria/archaea domains) - resulting in cell division (mitosis).

Question 8

Explain the crossing over

Answer 8

1) Homologous chromosomes are duplicated (before meiosis).
2) Crossing over of the chiasms orders recombination in the order of alleles - impacting genetic diversity - increasing potential gene pool.

Question 9

Outline the key differences between mitosis and meiosis.

Answer 9

Mitosis Meiosis
- one cell division - two cell divisions complete the
completes the process. process.
- two cell output. - four-cell (gamete) output.
- each daughter cell has - each daughter cell has haploid
diploid number of number of chromosomes.
chromosomes.
- asexual - sexual