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Genetic Information and Variation - Coggle Diagram
Genetic Information and Variation
DNA
Chromosomes are thread-like structures made up of a combination of DNA and proteins called histones.
DNA is a very long molecule and so must be packed tightly. So the DNA-histone complex (also called a
NUCLEOSOME
) is coiled, then nucleosome coils are also coiled again to make it even tighter.
DNA double helix structure is wound with histones to make a nucleosome, nucleosomes are coiled up into coils, which are coiled into supercoils which make up a chromosome.
Chromosomes structure (eukaryotic) : two identical
chromatids
(exact replicas formed during DNA replication). Chromatids are made of supercoiled DNA with histones. The point where two chromatids meet is called the
centromere
.
DNA in Eukaryotic chromosomes is
linear and longer than in prokaryotes
Prokaryotic Cells
Prokaryotes carry DNA as chromosomes but it is
short and circular
(NOT LINEAR). The DNA is not wound around histones, it is just condensed due to supercoiling.
Mitochondrial and Chloroplast DNA
Mitochondria and chloroplasts carry their own DNA (which is similar to prokaryotic DNA), it is short and circular and isn't wound around histones. Their DNA codes for proteins and enzymes which are needed for processes such as respiration and photosynthesis.
This adds to the endosymbiotic theory: the theory says that mitochondria and chloroplasts were prokaryotic in the past, but made their way into eukaryotic cells, which then formed a symbiotic relationship.
Mitochondrial DNA is only inherited from the mother since, it is only in an egg cell, not in a sperm cell. Some diseases are only passed on from mother to daughter. For example, Kearns-Sayre syndrome (the progressive deterioration of muscles in the eye and then the rest of the body as well as the degeneration of the retina in the eye).
RNA and the Genetic Code
Transcription
Genes and Chromosomes
Genes - Sequences of DNA, coding for a polypeptide or functional RNA.
Different polypeptides have a different order and number of amino acids so all genes are different lengths.
genes which don't code for polypeptides code for functional RNA which form ribosomes (rRNA) and molecules called transfer RNA (tRNA).
The entire set of genes in a cell is a genome and the entire set of proteins the cell can produce is the proteome.
Within a gene (whether its coding for a polypeptide or not) there are non-coding sections called
introns
, the coding parts are called
exons
.
EX
ons = The real gene (
EX
pressed/coding DNA)
INtrons = The junk/ not useful (INbetween sequence)
Outside of genes, eukaryotic DNA also contains DNA sequences which repeat over and over. These are called
NON-CODING MULTIPLE REPEATS.
Translation
Mutations