Biology B3

Cells

• Cytoplasm where chemical reactions take place
• A cell membrane which allows movement in and out of the cell
• A nucleus which contains the genetic information and controls what the cell does
• Mitochondria- respiration takes place here supplying energy. Cells with high energy requirement eg sperm, muscle and liver cells have large numbers of mitochondria

Ribosomes are too small to be seen under a microscope. They are in the cytoplasm and are the site of protein synthesis.

DNA

• DNA is two strands coiled to form a double helix, each strand containing bases made up of A-T G-C.
• Chromosomes are long, coiled molecules of DNA divided up into regions called genes.
• Each gene contains a different sequence of bases and codes for a particular protein.
• The base sequence determines the amino acid.
• Three bases =  one amio acid.

The code needed to produce a protein is carried from the DNA to the ribosomes by a molecule (mRNA) A copy of a gene is needed because the gene itself cannot leave the nucleus. DNA controls cell function by controlling the production of proteins, some of which are enzymes.

Watson and Crick

They used data from other scientists to build a model of DNA to include an X-ray showing the double helix and other data indicated that the bases occured in pairs.

New discoveries like Watson and Cricks are not accepted or rewarded immediately as it's important that other scientists can repeat their work and get similar results.

Proteins

Functions:

• Structural eg collagen
• Hormones eg insulin
• Carrier molecules eg haemoglobin
• Enzymes

Enzymes

• Biological catalysts
• Catalysing chemical reactions occuring in living cells: Respiration, photosynthesis, protein synthesis
• Having a high specificity for their substrate

How emzymes are affected:

• Low temperatures = lower collision rates
• Enzymes denature at extremes of pH and high temperatures
• Denaturing is an irreversible change, the active site changes shape

The bonds holding the shape of the protein break when exposed to high temperatures or extreme pH's. The active site denatures and the lock and key mechanism no longer works.Enzymes have an optimum temperature and pH, changing the temperature or pH means the enzyme becomes less effective,

Measuring the rate of a reaction

The rate of an enzyme-controlled reaction can be expressed as a Q10 value.

Q10 = Rate at higher emperature/rate at temperature

Mutations

• Gene mutations are changes to genes.
• They can be spontaneous  or increased by environmental factors such as radiation.
• Gene mutations may lead to the production of different proteins.
• Only some of the full set of genes in used n any one cell, some genes are switched off.
• Most mutations are harmful but some can be beneficial.

Aerobic respiration

Aerobic respiration is the release of energy from glucose in the presence of oxygen. Respiration results in the production of ATP which is used as the energy source for many processes in cells.

C6H1206 + 6O2 ---> 6CO2 + 6H20

Aerobic respiration requires oxygen and so the rate of oxygen consumption is an estimate of metabolic rate. Respiration is an…