Synthesis and Release of Protein

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Synthesis and Release of Protein
Mr G Davidson
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Variety of Protein

• Proteins are important molecules in biology.
• They contain the elements Carbon, Hydrogen,
  Oxygen and Nitrogen.
• They often contain Sulphur and Phosphorous.

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Variety of Protein

• Proteins are built from chains of amino acids,
  held together by peptide bonds forming
  polypeptides.
• If the polypeptides form parallel strands,
  fibrous proteins are formed, and if they become
  tangled up to form a spherical shape, globular
  proteins are formed.

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Variety of Protein

• Proteins form many different parts of an organism
  and have many functions.
• e.g. -enzymes, antibodies, structural,
  hormones, etc.

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Structure of DNA

• Cell proteins are built according to inherited
  information held in the nucleus, the information
  is packaged as chromosomes.
• The chromosomes are made up of chains of
  molecules, called genes.
• A gene is a unit of heredity and is composed of a
  complex substance called Deoxyribonucleic acid.

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Structure of DNA
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Structure of DNA
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Structure of DNA

• The DNA molecule can be described as a double
  helix.
• It is made up of two strands of sub-units called
  nucleotides.
• Each nucleotide has 3 parts
• deoxyribose sugar
• a base
• phosphate 

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Structure of DNA

• There are four different nucleotides, because
  there are four different bases.
• The four bases are
• Cytosine
• Guanine
• Adenine
• Thymine

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Structure of DNA

• The molecule is held together in two different
  ways.
• A strand is connected by strong bonds between the
  sugar and phosphate.
• The strands are held together by weak hydrogen
  bonds connecting cytosine to guanine and adenine
  to thymine.

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DNA Replication

• During cell division, the genes must be able to
  replicate in order that each new cell gets a full
  chromosome compliment.
• In order for replication to occur, the following
  must be present in the nucleus of the cell
• a supply of nucleotides (4 types)
• ATP
• a DNA molecule to copy
• appropriate enzymes

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DNA Replication

• Replication begins with the uncoiling of the DNA
  helix.
• Once this has happened, the weak hydrogen bonds
  joining the two strands break, causing the DNA
  molecule to unzip.
• Once the bases are exposed, free nucleotides find
  their complimentary bases, forming two new DNA
  molecules, identical to the original molecule.

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DNA Replication
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Protein Synthesis

• The sequence of bases along a strand of DNA is
  anything but random.
• The order of bases is called the genetic code.
• The code is actually a recipe for protein
  production.

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Protein Synthesis

• Proteins are chains of amino acids of which there
  are twenty in nature , so it follows that the DNA
  code should be able to specify at least 20
  different items.
• To do this, the bases of DNA are grouped in
  threes, these are called triplets of bases, each
  containing a triplet code for a specific amino
  acid.

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Protein Synthesis

• DNA occurs in the nucleus of a cell, and protein
  synthesis on the ribosomes in the cytoplasm,
  therefore something must happen which transfers
  information from one place to another.
• Protein synthesis occurs in two stages
• -transcription
• -translation

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Transcription

• The information contained in the DNA code has to
  be collected and taken out of the nucleus and
  this is done by another nucleic acid called
  Ribonucleic Acid (RNA).
• It is similar to DNA except
• 1. it is a single strand
• 2. it has a ribose rather than a deoxyribose
  sugar
• 3. the base Thymine is changed to the base Uracil

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Transcription

• There are two types of RNA
• 1. messenger RNA (mRNA)
• 2. transfer RNA (tRNA)
• During protein synthesis, the appropriate region
  of DNA temporarily opens up to expose the bases
  to produce a strand of mRNA which then leaves the
  nucleus through the pores.
• The mRNA template is made of triplet bases called
  codons.

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Translation

• Once the mRNA leaves the nucleus, it becomes
  attached to a ribosome.
• In the cytoplasm, there are still tRNA molecules
  containing only 3 bases called an anticodon,
  which corresponds to a specific amino acid.

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Translation

• The codons of the mRNA pair up with the
  anticodons of the tRNA which is carrying an amino
  acid.
• The amino acids are then joined together by
  peptide bonds to form proteins.

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Protein Synthesis
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Protein Secretion

• Many of the enzymes and other proteins made by
  the cell will have to be secreted by the cell
  since they may be used in remote parts of the
  organism.
• These proteins are processed by the Golgi body
  where carbohydrates are added to form
  glycoproteins.
• These are then pinched off to produce vesicles
  which are then transported to the plasma membrane
  where they are secreted.

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Protein Secretion