Download The Nucleus, Chromosomes and Genes

The Nucleus, Chromosomes and
Genes
Do you know the difference
between:
• A gene
• A chromosome
• A DNA molecule?
Discuss and report back…..
Finding your way around the cell
cell
Do you remember the
function of the nucleus?
CONTROL
nucleus
What is in the nucleus?
1 Chromosome
Chromosomes are made of a chemical called DNA
What is a gene?
Several genes
One
chromosome
A gene is a short part of a chromosome that is a coded
instruction for a single protein which influences
features e.g. eye colour
The chromosome
The chromosome has several genes (instructions)
encoded along its length.
Chromosomes
Only clearly visible when the cell is
dividing
End of section
Link to genetic
code
How many chromosomes?
We have two copies of each chromosome. One copy we inherit
from our father and one copy we inherit from our mother.
Is each pair of chromosomes
identical?
Eye colour
Blue allele
Eye colour
Brown allele
The chromosomes in a pair do contain the same genes.
But sometimes in different versions: ALLELES
Sets of chromosomes
This nucleus
is DIPLOID
2 sets
This nucleus has two sets of chromosomes.
3 are inherited from the father
3 are inherited from the mother
To give a total of 6
The Genetic Code
The chromosome
One chromosome = one molecule of DNA
The chromosome
The chromosome has several genes (instructions)
encoded along its length.
One GENE codes for one PROTEIN
The protein is assembled in the
cytoplasm by structures called ribosomes
which read the code.
1 gene = 1 protein
Uses of Proteins
Proteins are used for
•Making new cells – structural proteins
•Making enzymes
•Making hormones and other signalling chemicals
Proteins are made from amino acids. There are about 20
of these. The exact order of amino acids in a protein
decides what job it can do.
Structure of DNA
Structure of DNA: 2
Structure of DNA: 3
The sequence of bases is
the code used for
assembling proteins from
amino acids.
Only one of the two
strands is read (the other
is only important in
copying the DNA
molecule before cell
division). To do this the
double helix partially
unzips to allow reading.
Bases
There are four bases:
Adenine
Cytosine
Guanine
Thymine
These base pair following rules:
A always base pairs with T
C always base pairs with G
Structure of DNA: 4
The bases are read in
threes. This is because
3 bases are needed to
code for one amino
acid.
Eg. ACG = alanine
Reading the DNA
Copy of a gene
Amino
acids
Ribosomes
Protein
CYTOPLASM
NUCLEUS
Explore the animation on the next
slide to firm up your ideas.
Mutations
These are changes in the sequence of bases that make up a
gene.
The protein coded for by the mutant gene will be altered.
Almost always it will not work as well as the normal version
of the gene
mutagen
Mutations are caused by:
1)
Radiation:
•natural (from the rocks and the Sun)
•manmade (form medical machinery, nuclear reactor
waste, bombs)
2)
Chemicals:
•tobacco tar, pesticides, some food toxins
3)
Inaccurate copying of genes as
chromosomes are copied prior to cell division.
Effects of mutation
A) If the mutation is in a normal body cell
Cell death or a change in its functioning. In the worst cases the
change in function leads to cancer. This is when a cell start to
undergo uncontrollable division to create a tumour.
B) If the mutation is in a sperm or egg cell
All the cells in the new embryo will possess the mutation.
Often this results in abnormal development or death. Very
occasionally the mutation will change the properties of the
protein that the gene codes for in a useful way (and the
offspring that have it will be at an advantage compared with
offspring with a normal version of the gene)