1.1 Nucleus - contains the
genetic information and
controls what the cell
does. It has a
from it, onto which
ribosomes are attached.
1.2 Cytoplasm - where most
chemical reactions take place, it
may contain mitochondria which
is where most energy is
released in respiration.
1.3 Cell membrane - controls
movement into and out of the cell.
1.4 Mitochondria - place of respiration,
provide energy for the life process. Liver
and muscle cells have particularly large
numbers of mitochondria because they
have a high energy requirement.
2.1 The nucleus of each cell contains a complete set of
genetic instructions called the genetic code.
2.2 Information is carried by genes on chromosomes,
which are long coils of a chemical called DNA.
2.3 The genetic code controls cell activity and,
consequently, some characteristics of the organism.
2.4 A DNA molecule is made up of two strands coiled
around each other in a double helix.
2.5 The genetic code is in the form of a chemical code
made up of four bases.
2.6 These bases bond together in pairs forming the links
which hold the two strands of DNA together.
2.7 Each gene in a DNA molecule contains a different
sequence of bases. The bases code for the structure
of different proteins that are needed for the growth
and repair of cells.
2.8 Proteins are made in the cytoplasm. The code,
carried in DNA, is in the nucleus. As DNA does not
leave the nucleus, a copy needs to be made and
transferred to the cytoplasm.
2.9 DNA controls cell function by controlling the
production of proteins, some of which are enzymes
3 Watson and Crick
3.1 This highly specialised structure was first put
forward in 1953 by James Watson and Francis
Crick. They used data from cyrstallography
experiments performed by Rosaland Franklin. The
data from her experiments helped Watson and Crick
develpo a model that fitted the data. The model
showed two chains wound as a double helix and
other data indicated that the bases occured in pairs.
3.2 The structure fitted the data so perfectly that it was
accepted almost immediately. Watson and Crick
were awarded the nobel prize for medicine in 1962
for thier discovery of the structure of DNA. Thier
discovery is considered the most important
biological work of the last century. It led to an
explosion of scientific advances including genetic
engineering and mapping the human genome.
4 Bases in DNA
4.1 The four bases in DNA are A, C, G, T. A always bonds with T
and C always bonds with G on opposite strands of the DNA
molecule. This is complimentary base paring.
4.2 Proteins are made up of chains of amino acids. The cell uses the amino
acid from food to construct them. When a cell needs to produce proteins
of a particular type, certain genes will be switched on. These genes and
their resulting proteins determine the characteristics of the cell.
5 Protein Synthesis
5.1 The sequence of bases in a gene
represents the order in which the cell
should assemble amino acids to make
5.2 A group of three bases represent one
amino acid in a protein chain. Each protein
has a different shape and function.
5.3 Proteins are synthesised by structures
called ribosomes. These are too small
to be seen under a light microscope.
The are located in the cytoplasm.
5.4 In order for the DNA code in the
nucleus to be translated as a new
protein by the ribosomes, a
'messenger' molecule needs to
travel from the nucleus into the
cytoplasm and then become
attached to a ribosome. The
molecule is called mRNA
5.5 1. mRNA constructed from DNA
template in nucleus.... 2. mRNA carries
code from original DNA into the
cytoplasm and becomes attached to a
ribosome.... 3. Ribosome'translates'
the code on mRNA and constructs a
sequence of amino acids.... 4. Amino
acids linked together as a long chain
protein, which is released from the
ribosome to carry out it's function.