Higher Biology
Unit 1 – Protein Synthesis
Learning Outcomes
Synthesis and release of proteins
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Proteins can be classified as fibrous (e.g. keratin) or globular (e.g.enzymes,
hormones, antibodies).
Conjugated proteins are globular proteins with non- – protein parts (e.g.
haemoglobin, chlorophyll).
Proteins are made up of amino acids and it is the sequence of amino acids that
determines the function (or job) of that protein
DNA Structure and Replication
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DNA REPLICATION IS IMPORTANT because when a cell needs to make a
new copy of itself, it is important that the new cell contains exactly same
genetic information so the new cell functions properly.
DNA is made up of a double helix composed of two-twisted nucleotide strands.
Each nucleotide consists of a deoxyribose sugar, a nitrogen base, and an
inorganic phosphate group.
The base Adenine always pairs with the base Thymine (A with T)
The base Guanine always pairs with the base Cytosine (G with C)
In DNA replication these stages occur in the nucleus are as follows:1.
DNA double helix unwinds
2.
Weak Hydrogen bonds between bases break
3.
Free DNA nucleotides pair with complimentary base pairs A-T, G-C
4.
Strong chemical bonds form between the sugar of one nucleotide and the
phosphate of another, forming a sugar-phosphate backbone
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Each original DNA strand and rewinds with one new DNA strand. This is
called semi-conservative replication
Genes are located on chromosomes, which are mainly composed of DNA.
DNA replication requires a supply of nucleotides, ATP, a template DNA strand,
and the appropriate enzymes
Protein Synthesis
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Protein synthesis is when protein is made e.g. salivary amylase (enzyme)
A substance called RNA copies the DNA code that is needed to make the
protein.
RNA is a single stranded molecule, containing ribose sugar instead of
deoxyribose
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RNA contains uracil instead of thymine. i.e., uracil pairs with adenine
These are the stages involved in Protein Synthesis
1. Transcription (Copying the DNA code) – occurs in the nucleus
a) DNA double helix unwinds
b) Weak Hydrogen bonds between bases break
c) Free RNA nucleotides pair with complimentary base pairs A-U, G-C
d) This copied code called mRNA leaves the nucleus through a pore
2. Translation (making the protein) – occurs at a ribosome
a) Every 3 bases on mRNA makes a triplet code for one amino acid.
These 3 bases together are called a codon
b) A substance called tRNA is found in the cytoplasm and every 3 bases
on tRNA is called an anti-codon, which is complementary to codons
c) Each type of tRNA molecule carries a specific amino acid and takes it
to the appropriate place on the mRNA
d) Eventually a long chain of amino acids is formed joined together by
peptide bonds making a polypeptide chain
e) The protein moves into the rough ER and then a vesicle transports it
to the Golgi body
f) In the Golgi body, the protein is processed and packaged and then a
vesicle transports it to the cell membrane where the protein is
secreted
Viruses
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Viruses are very small and contain DNA or RNA surrounded by a protein coat
Viruses can alter (host) cell metabolism so that replication of viral DNA/RNA can
take place resulting in the release of large numbers of viruses. (Cell lysis)
The stages of a virus entering a cell include:1.
Attachment – the virus attaches to the cell
2.
Penetration – the DNA or RNA is injected into the cell
3.
Replication – DNA replication occurs
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Protein Synthesis – the protein coats are made
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Assembly – the protein coats surround the DNA
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Cell Lysis – the viruses are released to invade more cells
Cellular response in defence in animals and plants
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There are 2 types of Cellular defence mechanisms in animals
Phagocytosis or Antibody Formation
Phagocytosis is a non-specific immune response and involves lysosomes inside
Phagocytes fusing with the foreign particle and digesting it.
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Antibodies (Y-shaped globular proteins) Are produced by lymphocytes in
response to the presence of foreign antigens
Immuno-suppresser drugs are given to transplant pati0ents to prevent them
producing lots of anti-bodies which will cause them to reject the organ
Cellular defence mechanisms in plants – plants can protect themselves by
producing a variety of compounds (including tannins, cyanide and nicotine), or
by isolating injured areas by means of substances such as resin.