B5 Growth and developement- making proteins and cell division Biology 21st Century Science GCSE

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Making proteins:

Key points:

·       They are made in the cytoplasm because the DNA is unable to leave the nucleus as it's too big

·       Because the cell needs to get the information from the DNA to the ribosome, a copy of the DNA needs to be made

·       This is called mRNA

    • The main differences between it and DNA are:
      • It is only made of one single strand, while DNA is made of two
      • mRNA is much shorter
      • DNA uses the base ‘Thymine’, while mRNA uses uracil
      • DNA has the sugar deoxyribose while mRNA has ribose
    • This mRNA is like a messenger that goes between the DNA (in the nucleus) to the ribosome in the cytoplasm

The process:

1.    The DNA strands ‘unzip’, and the mRNA molecule is made using one strand of the DNA as a template (the base paring i.e. A and T, G and C) ensures there’s an exact match)

2.    Then, the mRNA molecule moves out of the nucleus, and joins together with a ribosome, found in the cell’s cytoplasm

3.    The mRNA molecule is then pulled through the ribosome like tape, who reads the molecule

·         Its job is to ‘stick’ the amino acids together in chains to make a protein

·         This is following the order of the bases in the RNA (i.e. every three bases codes for one amino acid, and the combination of these bases decides the amino acid)

Cell division:

There are two different types of cell division. In both processes, the first step is to copy everything i.e. all the chromosomes and organelles within the cell. This happens as follows:

1.    The number of organelles increases

2.    The chromosomes are copied, so the cell now has two copied of DNA:

a.     The molecule of DNA splits

b.    The bases on the free-floating nucleotides pair up with matching bases found on the DNA

c.     Between the bases and the


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