TOPIC%204:%20GENETICS

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TOPIC 4 GENETICS
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4.1 Chromosomes, genes, alleles and mutations

• ?State that eukaryote chromosomes are made of DNA
  and proteins.
• ?Define gene, allele and genome.
• ?Define gene mutation
• ?Explain the consequence of a base substitution
  mutation in relation to the processes of
  transcription and translation, using the example
  of sickle-cell anemia.

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4.1 Chromosomes, genes, alleles and mutations

• Review
• During the phase of the cell cycle known as
  interphase, chromosomes are in long thin threads
  called chromatin.
• We can only see DNA under large microscopes when
  chromatin condenses to form chromosomes.
• Eukaryotic cells (plants and animals) contain
  chromosomes, surrounded by a nuclear envelope.

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4.1 Chromosomes, genes, alleles and mutations

• New
• The chromosomes of eukaryotic cells are
  associated with proteins.
• Each chromosomes contains a single molecule of
  DNA along with these associated proteins.
• Some proteins are structural (ex histones) and
  others regulate DNA activities.

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4.1 Chromosomes, genes, alleles and mutations

• Review
• DNA is a sequence of nucleotides, held together
  by weak hydrogen bonds between the bases.
• This sequence of bases contains the genetic code
  in the form of triplets of bases.
• A triplet of bases in the DNA is transcribed into
  a triplet of bases in the mRNA, which is then
  translated into a specific amino acid.

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4.1 Chromosomes, genes, alleles and mutations

• New
• Gene a heritable factor that controls a specific
  characteristic, or a section of DNA that codes
  for the formation of a polypeptide.
• Allele a specific form of a gene occupying the
  same position on the DNA as other alleles of that
  gene, but differing by small differences in its
  base sequence.
• Genome the entire genetic information of an
  organism. (human genome has 20,000-25,000 that
  serve as directions to build all our proteins)
• Gene mutation a change in the sequence of bases
  in a gene.

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4.1 Chromosomes, genes, alleles and mutations

• Mutations
• DNA replication can be tricky a nucleotide can
  be left out, an extra one may be added, or the
  wrong one inserted.
• These mistakes are called gene mutations.
• The insertion of an incorrect nucleotide is
  called a base substitution mutation.
• When the DNA containing the incorrect nucleotide
  is transcribed and translated, errors can occur
  in the polypeptide.

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4.1 Chromosomes, genes, alleles and mutations

• Mutations
• If you look at a codon chart, many codons code
  for the same amino acid so many substitution
  mutations have no effect on the polypeptide that
  is produced.
• EX UCU, UCC, UCA, UCG all code for Serine, so
  if there was an incorrect nucleotide substitution
  in the last slot of the codon, Serine would
  still be placed in a polypeptide.

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4.1 Chromosomes, genes, alleles and mutations

• Cystic Fibrosis
• A deletion of 3 nucleotides that results in a
  loss of the amino acid phenylalanine at the 508th
  position of 1,480 amino acids on that specific
  protein.
• The protein that is incorrectly made should
  regulate and control components of sweat and
  mucus.
• Heavy mucus in lungs builds up, and is 80 cause
  of death in CF patients.

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4.1 Chromosomes, genes, alleles and mutations

• Cystic Fibrosis
• Mucus in the sinuses builds up, blocking passage,
  leading to infection, inflammation and breathing
  difficulties.
• Also, bile secreted by the liver and pancreas to
  aid in digestion may block the bile ducts,
  causing a build up and failure to rid the blood
  of toxins.
• This all results from these people having 3
  nucleotides deleted among 4,440 in a single
  protein!

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4.1 Chromosomes, genes, alleles and mutations
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4.1 Chromosomes, genes, alleles and mutations

• Sickle Cell Anemia
• Point mutation in the DNA

Sickle Cell Anemia Original/Good Mutation
DNA CTC CAC
mRNA GAG GUG
Amino Acid Glutamic Acid Valine
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4.1 Chromosomes, genes, alleles and mutations

• Sickle Cell Anemia
• Blood disorder where red blood cells (RBC) become
  sickle shaped (look like a half moon) and cannot
  carry oxygen properly.
• These RBC lose their elasticity and flexibility
  because Glutamic Acid is hydrophilic and Valine
  is hydrophobic.
• This change of polarity causes the RBC membrane
  to change shape and become rigid, so they don't
  pass through capillaries easily.

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4.1 Chromosomes, genes, alleles and mutations

• Sickle Cell Anemia
• The mutation doesn't make the correct protein
  hemoglobin. This protein is how the RBC carry
  oxygen to other tissues.
• The RBC odd shape results in clots and allows
  them to deliver less oxygen because the surface
  area to volume ratio is affected.
• Symptoms fatigue, rapid heart rate, shortness of
  breath, kidney problems and possible infections.

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4.1 Chromosomes, genes, alleles and mutations

• 1. What is meant by the term 'base substitution
  mutation' and 'silent mutation'.
• 2. Find 3 'silent mutations' using your codon
  chart. Give the normal amino acid and the amino
  acid after the mutation.
• EX normal codon CAU Histidine
• silent mutation CAC Histidine

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4.1 Chromosomes, genes, alleles and mutations

• 3. In the normal allele for hemoglobin, there is
  a triplet on the coding strand of the DNA that is
  C-T-C. In people suffering from sickle cell
  anemia, what has this triplet mutated to?
• 4. Because of this mutation, one amino acid in
  the polypeptide chain in hemoglobin is abnormal.
  Name the normal amino acid and the amino acid
  that is from the sickle cell mutation.
• 5. Explain why this mutation leads to
  sickle-cell anemia