Genes and Chromosomes

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Chapter 10

• Genes and Chromosomes

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Structure of DNA

• I. DNA (Deoxyribonucleic Acid) is made of
• Nucleotides (3 parts)
• 1.Deoxyribose (simple sugar)
• 2.Phosphate Group
• 3.Nitrogen Base(A, C, T or G)
• ADENINE
• CYTOSINE
• THYMINE
• GUANINE
• Alt --gt T
• C lt--gt G (COMPLIMENTARY)

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• DNA Chains (2 strands) of nucleotides joined by
  hydrogen bonds between bases twisted ladder gt
  DOUBLE HELIX
• A. DNA Replication Each organism has its
  unique nucleotide sequence in its DNA ---gtfrom
  parents
• DNA must be copied
• for cell division
• (chromosomes replicate)

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• STEPS IN DNA REPLICATION
• Enzymes break bonds between bases - DNA unzips
• Free nucleotides in nucleus pair up with exposed
  bases (complimentary)
• 2 new strands formed and rewind (identical to
  original DNA)

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Protein Synthesis

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The DNA code builds a protein. Proteins are made
up of amino acids.

• 3 nitrogen bases together represent a code called
  codon

• A codon can represent
• A start command
• A stop command
• A specific amino acid

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RNA Ribonucleic Acid

• A nucleic acid
• Single strand (not double like DNA)
• Different sugar molecule
• Uracil instead of thymine
• JOB 1. Acts as a messenger to deliver DNAs
  message
• 2. Used to build a protein.

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TRANSCRIPTION Enzymes make RNA from a strand of
DNA

• 1. DNA uncoils
• 2. DNA unzips
• 3. One side of DNA used to make RNA
• Now this RNA called messenger RNA (mRNA) travels
  to the ribosome to build a protein using the help
  of ribosome RNA (rRNA)

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Translation Making a specific protein from the
mRNA

• Transfer RNA (tRNA) brings amino acids over to
  the ribosome to hook up with the mRNA. When a
  match is made the amino acid stays. Eventually a
  chain of amino acids is produced PROTEIN

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GENETIC CHANGES

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• A. MUTATION A CHANGE
• 1. POINT MUTATION Change in a single base pair
  - can change the entire protein
• example normal---gt AUGAAGUUUGGC
• point mutation---gt AUGAAGUAUGGC

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2. Frameshift mutation Deletion or addition of
one nitrogen base that changes all the amino
acids that come after it.

• 3. Chromosomal mutation Adding or deleting
  part(s) of a chromosome (lots of nitrogen bases
  involved.)
• -These are usually due to mistakes in meiosis.
• -The zygote would usually die (miscarriage).
• Nondisjunction Mistake in the separating of
  chromosomes during meiosis.

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• Examples of non-disjunction
• 1. TRISOMY gamete (sex cell) has an extra
  chromosome so the human zygote will have 47
  chromosomes.
• Example Trisomy 21 Down Syndrome

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• 2. MONOSOMY A sex cell with 22 chromosomes
  combines with a sex cell with 23 chromosomes.
  The human zygote has 45 chromosomes. This zygote
  will not make it miscarriage.

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4 Types of chromosome mutations

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• A. DELETION part of chromosome left out
• ex ABCDEFG --------gt ABCEFG
• B. INSERTION duplication of certain genes
• ex ABCDEFG ----------gt ABCBCDEFG
• C. INVERSION part of chromosome breaks off and
  is reinserted backward
• ex ABCDEFG ------------gtADCBEFG
• D. TRANSLOCATION part of a chromosome breaks off
  and is added to a different chromosome
• ex ABCDEFG ----------gt WXABCDEFG

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What causes mutations?

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• SPONTANEOUS MUTATIONS Random, mistakes or
  changes in the DNA sequences This is a
  fundamental supporting principle of evolution
• ENVIRONMENTAL MUTAGENS AGENTS U.V. light,
  X-rays, Radioactive substances..These cause
  mutations that may or may not be transferred to
  the offspring!.