B5-Growth and Development

  • Created by: kira
  • Created on: 06-03-11 18:58

Growth and developmet-B5

*notes taken from the CGP revision guide.

DNA-Making proteins

  • A DNA molecule has two strands coiled together in the shape of two spirals.
  • Each strand is made up of lots of small groups called nucleotides.
  • Each nucleotide conatains a small molecule called a base. DNA has four different bases-adenine(A), cytosine (C), guanine(G), and thymine(T).
  • The two strands are held together by the bases, which always pair in the same way-A-T and C-G. This is called base pairing.
  • DNA controls the production of proteins in a cell.
  • A gene is a section of DNA that contains the instructions for one particular protein.
  • Cells make proteins by joining amino acids together in a certain order.
  • Its the order of the bases in a gene that tells the cell in what order to put the amino acids together.
  • Each set of three bases (a triplet) codes for one amino acid.
  • DNA determines which genes are switched on or off-and which proteins the cells the produces.
  • Proteins are made by Ribosomes. Proteins are made in the cell cytoplasm by organelles called ribosomes.
  • DNA is found in the cell nucleus and cannot move out of it becasue it's really big.
  • The cell needs to get the infomation from the DNA to the ribosome.
  • A copy of the DNA is made using a molecule called RNA., which is similar to DNA but its much shorter and only a single strand. RNA is like a messenger between DNA in the nucleus and the ribosome in the cytoplasm.
  • Here is what happens:

1) The two DNA strands 'unzip'. A molecule of RNA is made using one strand of DNA as a template. Base pairing makes sure its an exact match.

2) The RNA molecule moves out of the nucleus and joins up with a ribosome in the cytoplasm.

3)The job of the ribosome is to stick amino acids together in a chain to make a protein, following the order of bases in the RNA.

Cell division-Mitosis:

  • New cells are needed for growth and repair. The cells of your body divide to produce more cells, so your body and grow and replace damaged cells. Cells can also happen in other animals. There are two stages:

1) First the cell has to copy everything it contains so that when it splits in half the two new cells will contain the right amount of material.

-The number of orgenalles increases during cell growth.

-The chromosomes are copied, so that the cell has two copies of its DNA.

2) The cell has two copies  of its DNA all spread out in long strings.

-Before the cell divides, the DNA forms x-shaped chromosomes. Each 'arm' of a chromosome is an exact duplicate of the other.

-The chromosomes then line up at the centre of the cell and cell fibres pull them apart. The two arms of each chromosome go to opposite ends of




Thank you

lisa linsdell


Some good revision notes on the OCR twentyfirst century science module B5. Contains information on DNA replication, cell organelles, mitosis, meiosis etc. Keywords and phrases highlighted. 



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