genetics recap & basics. dna structure function replication
Post on 16-Dec-2015
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GENETICS
Recap & Basics
DNA
• Structure
• Function
• Replication
Structure of DNA
•Deoxyribose sugars joined by Phosphate bonds
•Bases – A, T, C, G bonded to sugars
•Two corresponding strands are joined together by weak bonds between bases
(A & T; C & G)
•Twisted into a double helix
Function of DNA
• Carries the genetic code for functioning of an organism
• The sequence of bases on one strand contains the genetic code for all proteins needed by an organism
• Three bases = a triplet; one triplet codes for one amino acid (protein is made up of chains of amino acids).
• Groups of triplets code for a protein = a gene.(gene is section of DNA that codes for a protein)
Packaging of DNA
• There is a lot of DNA in cells, especially in eukaryotes.
• It has to be wound around proteins to make it fit into the cell.
• Usually DNA occurs as chromatin fibres within cells.
• Before replication, chromatin fibres condense to form chromosomes.
Replication of DNA
• DNA in cells replicates itself before cell division.
• Mitosis: cell division for growth and repair
• Meiosis: cell division for sexual reproduction
• Cell division
Chromosomes
• In somatic cells, chromosomes exist in homologous pairs (one from father and one from mother).
• Humans have 23 pairs – so 46 chromosomes.
• One half of the pairs is a set called the haploid number, n. Two sets are diploid, 2n.
• In gametes (egg & sperm) there is only a haploid number of chromosomes.
Genes• Genome is the total amount of genetic material
an individual has.
• One gene codes for one protein.
• It is possible to have variations of the same protein. These arise from variation of the same gene.
• Different varieties of the same gene are called alleles.
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