Molecular Genetics: DNA

1
Molecular Genetics DNA

• Four roles for DNA
• Information storage
• Replication (reproduction)
• Day to day instructions to the cell
• Mutation

2
Molecular Genetics DNA

• Pro- and eukaryotic genes are organized
  differently.
• Prokaryotic genes are tightly-packed and
  streamlined.
• Eukaryotic genes are spread out and hard to
  control, much more complex.

3
The Circular Genome of E. coli
Almost no waste DNA between genes Few repeated
DNA sequences Genes that have to work together
are close to each other Controlled as a unit-
an operon
Genes for lactose metabolism make up an operon
4
Eukaryotic genes and genomes

• Generic gene for an mRNA reveals important
  features
• Interrupted genes (introns and exons)
• Many control regions
• Much wasted DNA

5
Example-globin

• Gene families
• Regulation must be coordinated
• Much non-coding sequence between genes

6
Example-globin

• Hereditary globin deficiencies are called
  thalassemia
• Less susceptible to lethal strains of malaria?
• Cooleys anemia

7
Molecular Genetics-summary of transcription

• DNA instructions are put into action by RNA,
  which is directly copied from a DNA molecule
• (transcription)
• Produces different types of RNA
• ribosomal RNA rRNA, messenger RNA mRNA,
  transfer RNA tRNA
• Some of the RNAs go on to produce protein
• Others have different jobs

8
Molecular Genetics-summary of transcription

• Trancription carried out by enzymes called RNA
  polymerases
• Very large enzymes that are under tight control
  by other proteins

9
Molecular Genetics-RNA processing

• RNA molecules must be heavily modified after
  transcription
• This is called RNA processing

10
Molecular Genetics-RNA processing

• Eukaryotic mRNA processing most complex
• Involves cutting and splicing of genetic
  information

11
Molecular Genetics-Roles of RNA

• All RNAs must be processed
• After processing, some of them are directly
  active as RNA molecules (rRNA, tRNA, regulatory
  RNAs)
• One type (mRNA) serves as physical carrier of DNA
  information that will be translated into protein

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Molecular Genetics-Roles of RNA

• At least 3 types of RNA required for translation
  of proteins
• rRNA structure and catalytic heart of ribosome
• tRNA brings amino acids to ribosome-adaptor
• mRNA carries DNA message to ribosome
• Regulatory RNAs are often needed as well

13
Molecular Genetics-tRNA

• Adaptor or interpretor-amino acids and mRNA
• Anticodon is complementary to an mRNA codon
• 3 end is covalently attached to an amino acid by
  an enzyme

14
Molecular Genetics-translation

• Message read one codon at a time
• tRNAs enter and leave successively
• Ribosome forms peptide bonds

15
Polyribosome or polysome
16
Gene Expression in Prokaryotes

• Expression mainly by controlling transcription
• Constitutive or housekeeping genes expressed
  continually-always on
• Other genes not produced continually
• Only on when needed

17
Operon organization

• Genes that work together are located together
• They are controlled as a unit
• Streamlined, efficient, saves resources

18
The genome is organized in units called operons
19
Eukaryotic gene expression

• Much more complex
• Many control sequences and proteins for each gene

20
Eukaryotic gene expression-transcription factors

• Many proteins must be present for gene to be
  active

21
Eukaryotic gene expression-transcription factors

• All your somatic cells have the same DNA
• Different tissues have different transcription
  factors-different genes are expressed

22
Endocrine disruptors

• Environmental pollutants that mimic hormones
• Interact with transcription factors to activate
  wrong genes
• Birth defects, cancer?