A complex molecule containing the genetic information that makes up the chromosomes.
The DNA in prokaryotic cells is significantly different from
from the DNA found in eukaryotic cells
DNA is
double-stranded
Prokaryotes possess one or more plasmids
Plasmids are very small circular DNA molecules They usually only contain a few genes Plasmids are more accessible for proteins required for gene expression and therefore contain genes that are required often , quickly and / or in emergencies The genes for antibiotic resistance are often found in plasmids
The DNA within which cells are associated with proteins (histones)
Eukaryotic DNA
Chromosomes The main proteins present are the
Histones - their role is to organise and condense the DNA tightly so that fits into the nucleus
chromatin
The tightly coiled combination of DNA and proteins
Makes up chromosomes
S phase
DNA replicates to create two identical strands of DNA called chromatids joined together by the centromere
The two chromatids that make up the double structure of a chromosome are known as
sister chromatids
Chromatids are identical because
They form 2 separate daughter cells after mitosis so this ensures that the daughter cells are genetically identical
Mitochondria
The site of aerobic respiration within eukaryotic cells
Has a double membrane with the inner membrane folded to form cristae. The matrix formed by the cristae contains enzymes needed for aerobic respiration producing ATP
Chloroplast
Chloroplasts, larger than mitochondria, are surrounded by a double membrane, with membrane-bound compartments called thylakoids which contain chlorophyll-stacked structures called grana, joined by lamellae.
They are the site of photosynthesis, with light-dependent stages occur in the thylakoids.
Light independent stage (Calvin Cycle) occurs in the stroma.
lamellae
thin and flat thylakoid membranes
gene
is a base sequence of DNA that codes for the amino acid sequence of a polypeptide or a functional RNA molecule
Functional RNA molecules are required for protein synthesis
mRNA the base sequences on messenger RNA molecules are used by ribosomes to form polypeptide chains tRNA - amino acids are carried to the ribosome by transfer RNA molecules rRNA - ribosomal RNA molecules form part of the structure of ribosomes
The shape and behaviour of a protein molecule depends on the
the exact sequence of these amino acids ( the initial sequence of amino acids is known as the primary structure of the protein molecule
primary structure
the initial sequence of amino acids is
The genes in DNA molecules therefore control protein structure
control protein structure ( and as a result , protei function ) as they determine the exact sequence in which the amino acids join together when proteins are synthesised in a cell
One gene codes for one mRNA molecule which codes for one polypeptide This
known as the central dogma of molecular biology
each chromosome in a human cell nucleus contains one very long DNA molecule This DNA molecule is made up of
thousands of specific nucleotide sequences called genes that code for specific proteins . Even though these genes are all found within the same DNA molecule and are therefore all linked up the cell knows where individual genes start and stop This ensures the cell reads the DNA correctly and can produce the correct protein molecules that requires to function properly
The DNA contained within chromosomes is essential
for cell survival
Every chromosome consists of a long
consists of a long DNA molecule that codes for several different proteins %
gene
A length of DNA that codes for a single polypeptide or protein FORMS
locus ( plural loci )
The position of gene on chromosome
Each gene can exist in two or more different forms called
alleles
Different alleles of a gene have slightly different nucleotide sequences but they still
they still occupy the same position ( locus ) on the chromosome
gene
is a sequence of nucleotide bases in a DNA molecule that codes for the production of a specific sequence of amino acids that in turn make up a specific polypeptide ( protein )
The DNA nucleotide base code found within a gene is a three multiple
three - letter , or triplet , code
Triplets (3 bases) are known as codons
Each codon codes for a different amino acid
Genetic code is degenerate
There are 64 different triplets possible, yet there are only 20 amino acids.
This results in multiple codons coding for the same amino which can limit the effect of mutations.
Genetic code is universal
The same codons code for the same amino acids in all living things.
There are 64 triplet codons which make up 20 amino acids.
Eukaryotic cells contains introns
Non - coding sections of DNA which does not code for any amino acids
Introns
Non-coding regions of DNA
Pre-mRNA to mRNA
Before the pre - mRNA exits the nucleus the introns are removed and the exons are joined together in a process called splicing.