Chapter 8, part A

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Chapter 8, part A

• Microbial Genetics

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Life in term of Biology

• Growth of organisms
• Metabolism
• Determined by the enzymes present in the cells
• DNA carry the information for the enzymes
• Multiplication of organisms
• Increase number of the population
• Heredity save the characteristics of the
  species
• DNA carry the the information

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DNA

• DNA molecules in the cells exist as a
  double-stranded helix
• The linear sequence of bases provides the actual
  information
• A,T,C, and G the four letters of genetic
  language
• Gene Segment of DNA that encodes a
  functional product, usually a
• protein (or
  functional RNA
• mRNA, rRNA,
  tRNA)

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Genetics

• Study of what genes are.
• How genes are replicated.
• How they carry information.
• How information is expressed.

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Terminology

• Genome All of the genetic material (DNA) in a
• cell
• Genomics Molecular study of genomes
• Genotype All genes of an organism. The genetic
• composition of an organism, its
  entire
• complement of DNA.
• Phenotype The expression of the
  genes, the
• proteins of the cell
  and the
• properties they
  confer on the
• organism

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The flow of genetic information

• The DNA in a cell is duplicated (replication)
  before the cell divides, so each daughter cell
  receives the same genetic information (DNA ? DNA)
• When a gene is expressed
• DNA is transcribed to produce RNA (mRNA, rRNA,
  tRNA),
• mRNA is then translated into proteins.
• DNA (gene )? Transcribed (RNA)
• RNA (mRNA) ? Translate (protein)

Gene expression
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DNA

• In eukaryotic cells the DNA exists as linear
  double helix molecules associated with various
  proteins that regulate genetic activity.
• One molecule - chromosome
• Different organisms have different number of
  chromosomes
• Human 46, East-32
• Bacterial DNA is one chromosome which is
  circular molecule, associated with different
  proteins.
• The chromosome of E. coli, for example, contains
  about 4 million base pairs and is approximately
  1000 times longer than the cell.
• Not all of the DNA encode genes

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E. coli
Figure 8.1a
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DNA

• Polymer of nucleotides Adenine, Thymine,
  Cytosine, Guanine
• " Backbone" is deoxyribose-phosphate
• Strands held together by hydrogen bonds between
  AT and CG
• Strands have 3 and 5 end
• Strands are antiparallel
• Double helix associated with proteins

Figure 8.4
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DNA replication

• Enzyme responsible for the replication is DNA
  polymerase
• During DNA replication, the two strands of the
  double helix separate at the replication fork,
  and each strand is used as a template by DNA
  polymerases to synthesize two new complementary
  strands of DNA according to the rules of
  nitrogenous base pairing.
• 5..AAGCTTA. 3
• 3..TTCGAAT. 5
• Because each daughter double-stranded DNA
  molecule contains one original and one new
  strand, the replication process is called
  semiconservative
• DNA polimerase makes mistakes with frequency 10-9
  - mutation

Figure 8.3
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DNA replication
Figure 8.6
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DNA replication

• DNA is copied by DNA polymerase
• In the 5? ? 3? direction
• Leading strand synthesized continuously
• Lagging strand synthesized discontinuously
• Initiated by an RNA primer
• Okazaki fragments
• RNA primers are removed and Okazaki fragments
  joined by a DNA polymerase and DNA ligase

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Bacterial DNA replication
Figure 8.7
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Transcription

• DNA is a template for transcription to synthesize
  RNA (mRNA, tRNA, and rRNA)
• Only genes are transcribed
• Enzyme responsible for the transcription of DNA
  is RNA polymerase
• Transcription begins when RNA polymerase binds to
  the specific DNA sequence - promoter
• Transcription proceeds in the 5? ? 3? direction
• Only one of the DNA strands is transcribed
• Complementary base are A-U (UTP) and G-C
• DNA 3.. AATCCGA . 5
• RNA 5. UUAGGCU.. 5
• Transcription stops when it reaches the
  terminator sequence

GENE sequence Promoter sequence ? coding sequence
? terminator sequence
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Transcription
Figure 8.8
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mRNA

• Eukaryotic genes consist of
• Exones coding sequence
• Intrones nonsence sequence
• mRNA is synthesize as a precursor and undergo
  splicing
• one mRNA more then one protein
• variability
• Bacterial genes dont have intrones

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mRNA processing in Eukaryotes
Figure 8.12
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Bacterial mRNA

• Bacterial genes dont have intrones
• Bacterial mRNA does not undergo splising
• Bacterial mRNA could carry sequences for more
  then one protein
• Transcription starts from one promoter
• mRNA AUG..Stop.AUG..Stop..AUGStop
• protein1 protein2
  protein3

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Flow of Genetic Information

• DNA gene with specific sequence of bases
• A, T, G, C
• RNA complementary to the DNA with bases
• A, U, G, C
• Protein sequence of 20 amino acids- code
• Genetic code
• Variability 4, 428, 4364
• Codons - three-base segments of mRNA that specify
  amino acids are called codons.
• All organisms have the same codons to specify the
  particular amino acid

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Translation
Translation is the process in which the
information in the nucleotide base sequence of
mRNA is used to dictate the amino acid sequence
of a protein.

• Who is the translator?
• Transfer RNA (tRNA).
• For each sense codon these is a tRNA with
  complementary antisense codon

Figure 8.2
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Translation

• The genetic code is degenerate that is, most
  amino acids are coded for by more than one codon.
  
• Of the 64 codons, 61 are sense codons (which
  code for amino acids), and 3 are nonsense codons
  (which do not code for amino acids and are stop
  signals for translation).
• The start codon, AUG, codes for methionine.
• Protein Met - Phe - Ser - ArgVal
• mRNA AUGUUUUCCAGGGUGUGA

Figure 8.9
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Iniciation of translation
Figure 8.9, step 1
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Translation
Initiation of translation AUG
codon Elongation Termination Stop codon
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Translation

• In Eukaryotic cells
• Transcription nucleus
• Translation - EPR
• In bacterial cells there is no nucleus
• The transcription and translation processes go
  simultaneously.

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Learning objectives

• Define genetics, genome, chromosome, gene,
  genetic code, genotype, phenotype, and genomics.
•  Describe how DNA serves as genetic information.
•  Describe the process of DNA replication.
•  Describe protein synthesis, including
  transcription, RNA processing, and translation.