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B3 Revision

Cells contain:-

- cytoplasm- where many chemical reactions take place.

- Cell membrane- controls movement in and out of the cell.

- Nucleus- contains genetic information DNA controlling what the cell does

- Mitochondria- respiration take place inside it, supplies energy for the cell.

Nucleus contains a complete set of genetic instructions. These are carried by genes on chromosomes. Genes are made from dna

DNA= deoxyribonucleic acid

Dna molecule is made up of 2 stands which form a double helix.

The genetic instructions form a chemical code made up of 4 bases (Adenine, Thymine, Cytosine & Guanine). These bond together forming cross links.

A bonds with T and C with G

Before cells divide the DNA is replicated meaning each new cell has a complete set of genetic information.

DNA Replication:-

  1. double helix unzips
  2. bases pair up
  3. an enzyme bonds 2 bases together forming complementary strands.
  4. 2 identical pieces of DNA are formed.

Protein synthesis-

DNA controls with proteins a cell synthesis (makes). Each gene code for a different protein.

Proteins are made from chains of amino acids. Cells use amino acids from your diet to make proteins.

Sequence of bases in gene represents order in which cell assembles amino acids to make protein.

Group of 3 bases represent 1 amino acid.

Each has different shape & function.

Liver changes some amino acids to others called transmission.

Essential amino acid- ones which you have to get in your diet because your body can’t make them.

DNA is used for identification in DNA fingerprinting. Blood from a crime scene can be compared with suspects DNA.

To make a DNA finger print you need:-

- isolation- DNA is extracted.

- Fragmentation- DNA is cut into fragments using restriction enzymes.

- Separation-DNA sections are separated using electrolysis.

- Comparison- compared with reference sample.

Enzymes are proteins acting as a biological catalyst, speeding up chemical reactions. They are very specific so each one will only speed up a particular reaction. Rate of reaction can be affected by temperature and PH.

A rise in temperature increases enzyme activity until optimum temperature is reached, temperatures above this can permanently denature enzyme molecules.

The optimum H for enzymes can vary.

Each enzyme has a different number and sequence of amino acids, resulting in different shaped molecules with different functions. Every enzyme has an active sight that only a specific reactant can fit.

When enzymes reach extreme temperatures or high PH the bonds holding the enzymes shape can break; the active sight is denatured and the lock and key mechanism doesn’t work.

Cells have to obtain oxygen, glucose, water and minerals from surroundings.

They have to get rid of waste products.

This is done via diffusion.

Diffusion is the net movement of particles from areas of high to low concentration.

Cells have…

- a low concentration of oxygen inside the cell.

- A high concentration outside.

Rate of diffusion is increased by increasing the surface area of the cell membrane; greater difference between concentrations; particles have


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