1.1 Mitochondria are structures in
cells where respiration
1.1.1 Ribosomes are too small to see
using the light microscope.
18.104.22.168 Chromosomes are made from DNA. Genes are
short sections of DNA. Each gene is a set of
coded instructions for making a particular protein.
1.2 Mitochondria are tiny structures found in cells (one is
called a mitochondrion). Respiration, the chemical
reaction that releases energy from glucose, happens in
mitochondria. This provides energy for life process
such as movement and growth.
1.2.1 Tissues and organs that need a lot of energy have large
numbers of mitochondria in their cells. For example, liver
cells and muscle cells contain a lot of mitochondria.
22.214.171.124 Some cell structures are too small to be seen with the light
microscope. Ribosomes are like this. They are found in the
cytoplasm and are the site of protein synthesis. They can only
be seen using an electron microscope.
1.3 Chromosomes: The cell's nucleus contains chromosomes.
These are long, coiled molecules of DNA, divided up into
regions called genes.
1.3.1 DNA: The information contained in genes is in the form
of coded instructions called the genetic code. The
genetic code controls cell activity, which means that it
also controls some characteristics of the organism.
126.96.36.199 DNA controls the production of different proteins. These are needed for the
growth and repair of cells.
1.4 Structure of DNA: Two scientists, James Watson and
Francis Crick, worked out the structure of DNA. By
using data from other scientists they were able to build
a model of DNA.
1.4.1 Each strand of DNA is made of chemicals called bases. Do not confuse these
with the bases you meet when you study acids and alkalis in chemistry. There
are four different types of bases, shown as A, T, C and G in the diagram.
188.8.131.52 In DNA, two strands coil together to form a double helix. There are
chemical cross-links between the two strands, formed by pairs of bases.
1.5 Genes and proteins Each gene in a molecule of DNA
contains: A different sequence of bases Codes for a
particular protein. Proteins are made in the cytoplasm of a
cell, not in the nucleus. Genes cannot leave the nucleus,
so a copy of the gene is needed. This copy is able to
leave the nucleus to go into the cytoplasm so that proteins
can be made by the cell.
1.5.1 The four bases of DNA are A, T, C and G. They always pair up in a particular
way, called complementary base pairing: A – T and G – C
1.6 Protein structure is determined by the DNA base code.
1.6.1 Proteins are made from lots of amino acids joined together. Each amino acid is coded by the sequence
(order) of three bases.
184.108.40.206 The sequence of bases determines the sequence of
amino acids in a protein molecule.
220.127.116.11.1 DNA controls the functions of a cell by controlling its production of
proteins. Some of these proteins are enzymes.
1.7 Messenger RNA (mRNA): Ribosomes are the site of
protein synthesis. They are found in the cytoplasm but
DNA is found in the nucleus. The genetic code needed
to make a particular protein is carried from the DNA to
the ribosomes by a molecule called mRNA.