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N5 Revision
Cell Biology
Cell structure
Animal Cell
Ribosomes
Cell membrane
Nucleus
Cytoplasm
Mitochondrion
Cell structure
Cell structure
Fungal Cell (yeast)
Cell structure
Bacterial Cell
DNA
Cytoplasm
Plasmids
Ribosomes
Cell wall
Cell membrane
Functions
Transport
Double layer of
phospholipid
Proteins
Protein channel
(Pore)
Some proteins allow molecules to pass through them easily – PORES
Some proteins are responsible for active transport of molecules
Diffusion
• Diffusion is defined as;
The movement of a molecules down a
concentration gradient from a high
concentration to a lower concentration.
• Diffusion is an example of passive transport;
Passive transport is the movement of molecules
down a concentration gradient from a high
concentration to a lower concentration, and
does not require energy for it to take place.
Active transport
• Active transport is;
The movement of molecules and ions against a
concentration gradient, from a region of low
concentration to a region of high concentration.
• Active transport requires energy for membrane
proteins to move molecules and ions against the
concentration gradient.
• For example, nerve cells need to pump sodium
out and potassium in.
Producing new cells
Stages
• Chromosomes are replicating
• Chromosomes shorten and thicken so they are
now visible
• Chromosomes line up at the equator and
spindle fibres attach at the centromere
• Chromatids are pulled apart to opposite sides
of the cells
• Nucleus reforms in each new daughter cell
and cytoplasm divides
DNA and the production of proteins
The structure of DNA is known as a double helix.
It has a 2 sugar phosphate back bones with
pairs of complementary bases held together.
DNA code
DNA carries the genetic code to make proteins.
This code is the order of the bases on the DNA
molecule.
The bases are adenine, thymine, cytosine and
guanine.
The DNA molecule is too important to carry the
code from the nucleus to the ribosome where
proteins are made, so a copy is made.
This copy is messenger RNA (mRNA).
It carries a complementary copy of the code to
the ribosome.
The sequence of the bases determines the order
of the amino acids, which makes the protein .
Different proteins are coded for by different
strands of DNA, so their order of amino acids
is different.
Types of proteins
Because of the different order of amino acids
making up the protein their shape is often
different.
The shape of a protein is different for different
types of proteins;
Structural – structural proteins in the body are
keratin found in hair and nails and collagen which
makes skin elastic.
Hormones – these are chemical messengers that
travel in the bloodstream.
Antibodies - these are Y-shaped molecules which
will bind to foreign cells allowing our immune
system to destroy them.
Enzymes
Enzymes are another type of protein in the body. They
are biological catalysts
They speed up chemical reactions in the body and are
unchanged in the process.
They work by
binding to the
substance they
are going to
work on
(substrate) and
holding it in the
active site.
The active site
The active site must have a complementary
shape to the substrate if they are going to fit
together. For this reason enzymes are specific
like a lock and key.
Enzyme activity
At low temperatures, enzyme activity is low as the
substrate and the enzyme are moving so slowly
they don’t get to meet very often to work.
As the temperature increases so does enzyme
activity, however, at high temperatures, the
enzyme’s shape is altered, meaning the active site
no longer matches the substrate shape.
The enzyme is denatured.
The temperature that the enzyme’s activity is the
highest is known as the optimum temperature.
Enzyme activity
Enzymes are also sensitive to changes in pH.
There will also be an optimum pH, and either
above or below this, will cause the enzyme to
denature.
Genetic engineering
Bacteria have plasmids which can be removed
and altered in genetic engineering.
We can add a human gene to the plasmid and
then after inserting it back into the bacteria,
have this genetically modified organism
produce a new substance for us.
Insulin is produced in this way.
3. Plasmid extracted
1.Chromosome extracted
and gene identified
2. Gene cut out by a
special enzyme
5. Gene inserted into plasmid and
sealed by an enzyme
6. Plasmid inserted into bacterial host cell
7. Genetically modified bacterium
grows and multiplies
8. Gene protein produced
by duplicates of plasmid
4.Plasmid cut open by
a special enzyme
Photosynthesis
Photosynthesis is a two-stage process.
Stage 1 – Light Reactions
Stage 2 – Carbon fixation
Light reactions
Light energy is trapped by the chlorophyll in
chloroplasts.
The light energy is used to split water into
hydrogen and oxygen and make ATP.
The ATP and hydrogen are used in the second
stage but oxygen diffuses out of the cell.
Carbon fixation
Carbon fixation is where hydrogen and
carbon dioxide are joined together to make
glucose.
Enzymes are essential in this stage.
The glucose can be used for respiration
immediately or it can be stored as starch or
used to make cellulose for cell walls.
Fermentation
When no oxygen is present in the cell,
fermentation occurs.
In plants,
Glucose
pyruvate
ATP
ethanol
+ CO2