Microbiology Ch 8

Gene - a segment of DNA that codes for 1 protein

Genome - all genetic info in a cell

Genotype - total genetic make-up - all alleles

Phenotype - organisms expressed genes

• Chromosome - physical structure that carries genes
• - - DNA + protein

• *1 circular molecule of DNA - double stranded + histone-like proteins
• *1 mm long (when uncoiled)
• *supercoiled (caused my hisone-like proteins)
• * found in the nuclear area of the cell
• * is attached to the cell membrane at one point

Replication - DNA make a copy of itself - 2 identical daughter cells - occurs in the nucleus

Occurs during the S (synthesis) phase of cell cycle - before cytokinesis (cell division)

• 1. 2 strands of DNA unzip = hydrogen bonds between base pairs are broken
• 2. Catalyzed by DNA polymerase - it joins nucleodies in the correct order
• 3. free nucleosides (extra P) floating in the nuclear cytosol bind complementarily to each strand
• 4. replication is is the 5' to 3' direction (bidirectional)
• - the leading strand is synthesized continuously by DNA polymerase
• - the lagging strans is synthesized discontinuously - RNA polymerase synthesizes a short RNA primer which is then extended by DNA polymerase (DNA polymerase digests RNA primer and replaces it with DNA)

• complementary pairing of nitroginous bases: A,T,G,C
• A:T
• G:C
• basis for the flow of genetic information
• Double helix is held together by hydrogen bonds as the base pairs

Backbone of pentose sugar and phosphates are held together by covalent bonds

• required for synthesis of DNA
• Proof reads DNA - if not correct it excises incorrect nucleotide and replaces it with correct one

energy needed for synthesis is in the P bonds of nucleosides

on DNA - site where replication occurs - DNA polymerase

Each new DNA strand contains one parent strand and one daughter strand

• synthesis of RNA - single stranded - occurs off one side (strand) of the DNA - in the nucleus
• mRNA - messenger - carries the code
• rRNA
• tRNA

• - Transcription begins when RNA polymerase binds
• at the promotor sequence on DNA

• - Transcription proceeds in the 5' to 3' direction
• -Stops at the terminator sequence on the DNA

- assembled from RNA nucleotides floating around

Translating the message in mRNA into a protein

mRNA travels out of nucleus - into cytoplasm to be translated on a ribosome

• 1. Ribosome runs along mRNA
• 2. Codons - 3 nucleotide sequences on the DNA are matched to Anti-Codons (3 complimentary nucleotides) on tRNA.
• 3. The tRNA is attached to a specific a.a.
• 4. a.a. are joined by peptide bond
• 5. Translation begins at start codon A,U,G
• 6. Translation ends at stop codon U,A,A or U,A,G, or U,G,A

20 different a.a. but 61 tRNAs (anti-codons) - code is degenerative - more than one anit-codon for each a.a.

Regulation of proteins systhesis is important - determines what biochemical reactions occur and uses ATP so some genes are only turned on when necessary

Constitutive gene - always on - 70% of genes

inducible - normally off but can be turned on

repressible - normally on but can be turned off

• Located on DNA - series are linked genes/ sites thought to regulate other genes responsible for protein synthesis
• 3 parts (1 & 2 controls 3)

• 1. promotor site = segment of DNA - if RNA polymerase binds to it - mRNA made
• 2. operator site =stop/ go point = if repressor binds to it then no mRNA made - no repressor = mRNA
• 3. structural gene site → codes for mRNA → protein

• Induction - mechanism that turns on gene expression
• - inducer - molecule that causes induction by inactivating repressor

• Repression - mechanism that inhibits gene expression
• = repressor = protein that blocks RNA polymerase - no mRNA made = no protein made

• Mutation = change in nucleotide sequence = abnormal protein
• sometime lethal or harmless - sometimes beneficial

• Mutagen - things that causes a mutation
• 1. chemicals
• 2. radiation

occasional mistake during DNA replication - 1 in 1 million

Point mutation - base substitution - results in wrong a.a. in protein (sickel cell)

nonsence mutation - nonsence codon created - no anit-codon so no protein made

frameshift mutation - 1 extra base inserted - changes all codon sequences

Ionising = high energy - free radicals destroy nucleotides

UV = fused thymines - thymine dimers (2) - DNA can replicate

Genetic recombination = crossing over (meiosis) - 2 chromosomes cross over - new combinations of genes

Bacteria takes in DNA from DEAD bacteria & incorporate in own DNA

Conjugation - bacteria to bacteria - transfer of plasmid though sex pili

• Transduction - bacteria + virus
• 1. bacterial cell infected by virus
• 2. virus reproduces itself
• 3. bacterial DNA - carried in head of virus (phage)
• 4. bacterial DNA introdiced into another bacteria when virus infects it

generalized = all of bacterias DNA is transfered

specialized = some DNA is transfered

Recombinant DNA - when recipiant cell incorporates new DNA into its own DNA

• Segments of DNA change position
• can move to
• 1. another part of same chromosome
• 2. a plasmid
• 3. DNA of another bacteria
• 4. DNA of another species of bactera
• 5. Phage head

transposans - code for enzymes that cut themselves out of parent DNA and reinsert themselves somewhere else