8.1 - 8.2 Genes, The Genetic Code, DNA and Chromosomes
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AS - Level Biology (8 - DNA, Genes and Protein Synthesis) Mapa Mental sobre 8.1 - 8.2 Genes, The Genetic Code, DNA and Chromosomes, criado por Bee Brittain em 16-03-2016.
8.1 - 8.2 Genes, The Genetic Code,
DNA and Chromosomes
GENES
A Gene is a section of DNA that codes for: 1) the amino
acid sequence in a poly peptide 2) Functional RNA (inc.
tRNA and rRNA)
A gene occupies a fixed position on the DNA molecule called a locus
The Genetic Code
20 Different A.A
4 Bases - Adenine and Thymine, Cytosine and Guanine
Three bases = One amino acid
64 Possible Codes
The code is DEGENERATE
This means that most amino acids are coded for by more than one triplet
One Triplet = One animo acid
The code is UNIVERSAL (mostly)
The same triplet codes for the same amino acid in most organisms
The code is NON-OVERLAPPING
Each base sequence is only once
Non-Coding regions
Multiple repeats of base sequences
Within Genes there are:
Introns - Non-coding regions
Exons - Coding regions
DNA
Prokaryotic
Circular
Shorter
Not associated with protein molecules
Don't have chromosones
Eukaryotic
Linear
Longer
Associated with proteins called HISTONES
Form CHROMOSOMES
Mitochondria and
Chloroplasts of eukaryotic cells also
contain DNA
This is like DNA of prokaryotes though
Chromosome Structure
1) DNA is a double helix
2) Helix is wound around histones to fix it in position
3) This DNA-Histone complex is then coiled further
4) The coil is the looped and further coiled and packaged into a CHROMOSOME
Chromosome contains a single molecule of DNA
Single molecule has many genes along it
Homologous Chromosomes
One chromosome from each homologous pair comes from the mother (maternal) and one comes from the father (paternal)
Homologous chromosomes are similar, but not identical
They have the same genes in the same order, for example: eye colour then hair colour. However they will have
different alleles, so the maternal chromosome may have blue eyes, then blonde hair, where as the dad could
have brown eyes and brown hair.