Transcript Chapter 6 Microbial Genetics

Microbial Genetics
• Slides are adapted from Dr. Gary Andersen,
Curtis Smith, KCKCC
• Reference: Chapter 7,8 from (Black, J., 2005)
Basic Units of Genetics
• Genomes – the total of the genetic material
in a cell.
• Gene - The unit of heredity for a given
genetic trait. The site on a DNA molecule
that carries the code for a certain cell
function.
• Viruses – 4 or 5 genes, E. coli – 4228 genes,
Human ~ 31,000 genes.
Nucleic Acids
I. Nucleic acids are located in the nucleoid
of bacteria, and the nucleus of eukaryotes.
There are 2 kinds of nucleic acids: RNA &
DNA.
Ruptured
E. coli cell
showing DNA
DNA
A. CHARACTERISTICS OF DNA
DNA(deoxyribonucleic acid) is made of subunits
called nucleotides. Nucleotides are made of 3
components. These 3 components are linked
together with a covalent bond.
E. Coli = 4.6 million nucleotide pairs (~1mm)
Corn = 2.5 billion nucleotide pairs
Human = 3 billion nucleotide pairs (2nm wide by 2
meters long)
Significance of DNA Structure
• Maintains the code with high degree of
fidelity. (double strand assures accurate
replication)
• Provides a method for introducing a high
degree of variety. (unlimited variety of
sequences possible)
1. COMPONENT 1 - Phosphate
Phosphate group - Phosphate functions as a
structural part of nucleic acids.
2. COMPONENT – Ribose Sugar
2, DEOXYRIBONUCLEIC
ACID
Ribose - A five carbon sugar that
functions as part of the DNA
backbone (ie. structural). “2,
Deoxy” means without oxygen
on the number 2 carbon atom.
3. COMPONENT – Nitrogen Bases
NITROGEN CONTAINING BASES
Function: express genetic information.
Composition :
2 PURINES:
ADENINE (A)
double ring structures
GUANINE (G)
2 PYRIMIDINES: THYMINE(T) CYTOSINE(C)
single ring structures
Nucleotide Base
Composed of one Nitrogen base, one Deoxyribose,
and one Phosphate group
Deoxyribose
Phosphate
Adenine
(Nitrogen base)
•
4 Nucleotides
D
N
A
S
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c
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e
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DNA Structure
4. DNA is a double helix (there are 2 strands of
DNA) which are intertwined with 5 base pairs
per turn.
5. DNA has complimentarity
that is
A always bonds with T
and
G always with C
6. DNA is always antiparallel. The 2 strands of
DNA are always oriented in opposite directions.
( 5’ PO3 end – 3’ OH end)
http://www.umass.edu/microbio/chime/dna/dna53.htm
DNA Bonds
•
3-D Image of
DNA
B. RNA
RIBONUCLEIC ACID
Similar to DNA except:
1. RNA is single stranded
2. RNA has a ribose sugar instead of
deoxyribose. (Oxygen on #2 C).
3. RNA has URACIL (u) instead of thymine
4. RNA is always shorter than DNA, ~ 1,000
nucleotides in length
•
C. FUNCTIONS OF RNA
1. rRNA (ribosomal) - comprises the ribosome
(site of protein synthesis). (60% of a ribosome
is made of RNA, the rest is protein).
2. tRNA (transfer) carries amino acids to the
ribosome during protein synthesis. Also
known as the “ANTICODON”
3. mRNA (messenger) - a complimentary strand
of RNA equal in size to 1 gene (normally ~1,000
nucleotides). “CODON” - coded info from
DNA (bound for the ribosome)
THE CENTRAL DOGMA OF
BIOLOGY “Francis Crick – 1956”
There are 3 parts to the flow of
information in all cells.
Transcription
Translation
DNA -------------mRNA-----protein
Replication
Central Dogma of Biology
DNA REPLICATION
1. Where 2 parental strands of DNA are
copied into 2 daughter strands. Rate =
1,000 nucs per seconds without error.
This leads to binary fission in bacteria.
Cell Division) = 2 daughter cells
2. Each cell receives 1 parental strand and
1 daughter strand. (semiconservative
replication)
GA sp 08
As the two replication forks meet, the two new chromosomes
separate—each containing one new and one old strand
Replication bonding
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1. EVENTS IN DNA
REPLICATION
a. DNA unwinds using the enzyme DNA
Helicase
b. SSBP holds the 2 strands apart (single
strand binding proteins)
c. Note: 2 replication forks. DNA
replication is considered bi-directional
replication.
DNA REPLICTION CONT’D
d. Polymerization requires DNA Polymerase
(POL III) which is an enzyme that synthesizes
2 nucleotide strands (daughter strands) from
2 parental (templates) strands.
e. DNA exonuclease (POL I) removes any
mistaken base pairs.
f. DNA ligase seals any gaps and joins the 2
strands together.
DNA Replication Enzymes at Work
•
Steps in Replication
•
Replication of DNA cont’d
Sit back!! We’re watching a
movie for a while
(But don’t expect too much)
Let’s watch some “interesting”,
academic movies
• Movie 1
• Movie 2
• Movie 3
THE CENTRAL DOGMA OF
BIOLOGY
There are 3 parts to the flow of information in
all cells.
Transcription
Translation
DNA --------------mRNA---------protein
Replication
B. TRANSCRIPTION
1. 2nd part of the central dogma of biology
2. 1st step in gene expression (i.e.protein
synthesis).
3. The cells genetic plan contained in DNA is
transcribed into a complimentary base
sequence called messenger RNA (mRNA).
4. The region of DNA that produces or serves as
a template for mRNA is called a gene. A gene
normally consists of around 1,000 base pairs.
It is the smallest segment of DNA that codes
for mRNA.
TRANSCRIPTION CONT’D
5. RNA polymerase is the enzyme
responsible for making mRNA
Transcription continued
7. Example:
DNA
DNA
mRNA
A T G C C G
T A C G G C
A UG C C G
8. mRNA is a blueprint of DNA or a
transcript or code.
9. One code word consists of three letters.
Animation of Transcription
• Movie 1
• Movie 2
• Movie 3
C. TRANSLATION
1. Translation is the 3rd part of the central dogma of
biology (2nd step in gene expression or protein
synthesis).
2. After transcription, the coded information in mRNA
is translated into an enzyme (protein).
3. This process takes place on the ribosome. Note that
the ribosome is made of rRNA and protein.
Translation Graphic
TRANSLATION CONT’D
4. tRNA STRUCTURE
tRNA utilizes the information in mRNA to
determine the sequence of amino acids in
a protein. tRNA has a cloverleaf shape.
The amino acid end binds one specific
amino acid in the cytoplasm. The
anticodon end pairs with the codon on
mRNA.
Transfer RNA Structure
TRANSLATION CONT’D
3. The mechanics of translation
Initiation; mRNA bumps into the small
subunit and triggers the two ribosomal
subunits to bind together. The first tRNA
anticodon (UAC) carrying the amino acid
methionine hydrogen bonds with the
codon AUG on mRNA.
TRANSLATION CONT’D
b. Elongation – The second tRNA
binds to the second code word on
mRNA. A peptide bond forms
between the two amino acids. The
first tRNA leaves, and the enzyme
translocase moves the ribosome
down one code word of mRNA at a
time. This repeats ~ 300X.
TRANSLATION CONT’D
In termination, one of three
possible stop codons is reached. The
last tRNA falls away and the two
ribosomal subunits fall apart.
C.
d. The Genetic Code
61 sense codons for 20 amino
acids
3 nonsense (or stop codons)
64total codons
Pg 180 (Black, J., 2005)
The Genetic Code
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Steps in Protein Synthesis
Steps in Protein Synthesis
Steps in Protein Synthesis
Steps in Protein Synthesis
Steps in Protein Synthesis
Protein Synthesis
Animation time..
• Movie 1
• Movie 1
Translation - Animation