Protein Synthesis

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Protein Synthesis

• DNA ? RNA ? Protein
  
• Transcription Translation

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DNA

• Basis for heredity from parents to
  offspring. Located in nucleus of cell.
• Regulates synthesis of proteins. Tells what
  particular polypeptide chain to make.
• Proteins are important in structure of
  organelles, plasma membrane, enzymes and
  hormones.

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Genetic Code

• Contains DNA which is a long twisted
  (double helix) molecule composed of nucleotides.
  DNA never leaves the nucleus.
• Nucleotides have a sugar group, phosphate group
  (PO4-2), and 1 of 4 nitrogen groups. These are
  adenine, thymine (uracil in RNA), cytosine, or
  guanine.

• The sugar and phosphate group make up the
  uprights and the nitrogen bases make up the
  rungs. (see diagram)
• Nitrogen groups pair up. Adenine with thymine
  and cytosine with guanine. This is called a
  nitrogen-base pair.

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DNA
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Genetic Code

•   When three base pairs are together, they
  form a triplet code which makes an amino acid.
  There are 20 amino acids altogether. (see
  diagram on board).
•   When 10 or more amino acids are formed,
  these form a gene. A gene is a section of DNA
  that contains all the triplet base pairs to code
  for one complete polypeptide chain.

• The genetic code is the message the gene
  provides to make a polypeptide chain.
• When 50 amino acids are formed, these form a
  protein. Examples are alanine, valine, cysteine
  and glycine.

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Genetic Code
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Protein Synthesis

• 2 processes of protein synthesis
• 1.Transcription
• 2.Translation

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1. Transcription

•   Process by which RNA is formed.
• DNA regulates protein synthesis and ribosomes are
  where proteins are manufactured.

•   DNA needs amino acids so we need breakdown
  of protein to get amino acids. So go to where
  proteins are manufactured which is the ribosome.
• During transcription, triplet code of DNA is
  transcribed (copied) onto an RNA molecule.

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Transcription
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Transcription

• 1 of 3 types of RNA is formed
• A. messenger RNA (mRNA)
• B. transfer RNA (tRNA)
• C. ribosomal RNA (rRNA)

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A. mRNA

• Exits nucleus through pores. Passes into
  cytoplasm and associates with ribosomes.

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B. tRNA

• Different structure then mRNA. It is a folded
  structure.
• Exits nucleus and passes into cytoplasm
• Transports free amino acids to ribosomes

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C. rRNA

• Still a different structure. It is spherical.
• Combines with proteins in nucleolus to form a
  ribosome.
• Exits into cytoplasm and remains as free
  ribosome or anchors to endoplasmic reticulum.
• Look at p. 68 fig. 3-17

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Transcription

• DNA DNA
• Cytosine Guanine
• Thymine Adenine
• Adenine Thymine
• Each triplet is an amino acid. This is a double
  helix.
• The mRNA comes in and unzips the double
• helix.Then you get the following.

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Transcription

• DNA RNA DNA RNA
• Cytosine Guanine Guanine Cytosine
• Thymine Adenine Adenine Uracil
• Adenine Uracil Thymine Adenine
• The triplet formed by the mRNA is
• called a codon.

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2. Translation

• The interpretation of the codon message in mRNA
  to a specific sequence of amino acids. Entirely
  done in the cytoplasm on the ribosomes.

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Translation

• A. mRNA attaches to ribosomes
• B. tRNA brings free amino acids. Only 2 tRNA
  at a time on mRNA. tRNA has triplet base called
  anticodon.
• C. Anticodon combines with complementary
  codon on mRNA

• D.Continues on down ribosome and peptide
  bonds are formed
• E.Sequence is stopped when stop codon is
  reached
• F.New protein is then formed

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Look at p.69 fig. 3-18

• Questions 136-156