What is DNA
Deoxyribonuucleic acid is a nucleic acid. It is a polymer of sub--units called nucleotides. It consists of 2 polynucleotide strands held together by hydrogen bonds to form an alpha double helix.
What is a gene?
A gene is a section of DNA that contains coded information as a specific sequence of bases.
Genes code for polypeptides that determine the nature and development of an organism.
What does a nucleotide consist of?
Each nucleotide consists of 3 molecules joined by a condensation reaction:
- A pentose sugar
- a phosphoric acid molecule
- an organice base
Which bases are complimentary to eachother and whi
A+T - Complimentary + Pyrimidine
C+G - Complimentary + Purine (double ringed bases)
Give the structures and their functions of DNA
- Sugar-phosphate backbone - gives strength
- Coiling of DNA - gives compact shape
- Double helix - protects sequence of bases + keeps molecule more stable
- Large molecule - Allows a large amount of information to be stored
- Many hydrogen bonds - give stability + prevents code being interrupted + allows chain to easily unzip for replication
- Sequence of bases - codes for synthesis of specific proteins
- Complimentary Base Pairing - enables information to be replicated accurately
What is an Allele?
An allele is a gene existing in a different form
What is a sequence of 3 bases known as?
A codon - these code for specific amino acids
- differ in their base sequence + code for different sequence of amino acids hence different polypeptides are produced
- This change in polypeptides makes the protein non-functional as there is a change in the tertiary structure of the protein
- This is because a change in the base sequence affects the hydrogen, ionics and (if present) disulfide bonds
- If the protein coded for is an enzyme, the shape of the active site may be altered and therefore the enzyme is non-functional as the substrate cannot attach and an enzyme-substrate complex cannot be formed
What is the haploid number? What is the diploid nu
Haploid = (n) 23
Diploid = (2n) 46
What 3 stages does the cell cycle consist of? expl
Interphase - represents the non-dividing cell when cell growth occurs
Nuclear division - the nucleus divides into 2 (mitosis) or 4 (meiosis)
Cell division - The cell divides into 2 (mitosis) or 4 (meiosis)
Describewhat happens during Interphase
During late interphase the cell prepares for division in the following ways:
- There is an increase in protein synthesis inside the cell
- The DNA content replicates via DNA replication
- Cell organelles are replicated
Descrine what happens during Prophase
Chromosomes form and become visable. Each chromosome consists of 2 identical chromatids.
Each chromosome shortens and thickens
Centrioles move to opposite poles of the cell and nuclioli and nuclear membrane break down
Describe what happens during Metaphase
Centrioles form a spindle across the cell - the spindle consists of protein microtubules
Each chromosome moves to the equator of the spindle and attaches to it via its centromere