Analytical Profile of Coleus Forskohlii | Forskolin .pdf
4 - Genetics
1. Genetic Material:
DNA and RNA
• DNA and RNA = hereditary material first
discovered in the nuclei of cells
• nucleotide “building blocks”
2. Nucleotides :
building blocks of DNA and RNA
1) Phosphate group
2) Sugar (deoxyribose or ribose)
3) Base
• Purines (A,G) two rings
• Pyrimidines (T,C,U) one ring
3. DNA structure:
the double helix
• Watson & Crick: DNA structure
Double stranded double helix
• Backbone = alternating sugar and
phosphate
• Bases form the “rungs” of ladder
• Complementary base pairing
4. DNA structure:
the double helix
Antiparallel strands
(opposite orientation)
3’ end = end with the –OH
attached to the 3’ carbon
5’ end = end with the
phosphate attached to the
5’ carbon
Strands run 5’---------3’
3’---------5’
6. RNA Structure
Different from DNA in that it:
• Is usually single-stranded
• Only double-stranded in some viruses
• A “rio” virus?
• DNA is single stranded in some viruses
• Contains ribose instead of deoxyribose
• Contains uracil instead of thymine
Three types found in cells:
• mRNA
• rRNA (ribosyl) 50S and 30S
• tRNA Bottom
is H a
7. Protein Synthesis
Question:
How is info from DNA used to dictate
the activities of the cell?
Answer:
expression of proteins through
transcription and translation
Transcription = synthesis of complementary RNA
from DNA
Translation = synthesis of proteins through
decoding of mRNA
8. Transcription: DNA to mRNA
Single stranded mRNA synthesized from DNA template
• Synthesized 5’ to 3’
• Complementary to template DNA
• Remember, uracil instead of thymine in RNA
Steps:
1. RNA polymerase binds the promoter
2. Synthesis continues until the terminator is reached
3. mRNA can now be used in the translation process
4. Operator:
10. Translation: mRNA to protein
Translates the nucleic acid
sequence into an amino acid
chain
Codons = groups of 3
nucleotides that “code” for a
particular amino acid
- Start codon = initiates
protein sythesis
- Stop codons = terminate
protein synthesis
Genetic code is degenerate because there are more codons than amino acids, they are not unique
Last letter is called a “wobble” because it
can change, but the chances the amino acid
will change is low
AUG codes for
11. Translation: mRNA to protein
The process of “reading” mRNA codons and generating the
amino acid chain takes place in the ribosome
tRNA molecules transport amino acids to the ribosome
• Anticodon = 3 base sequence complementary to a codon
- pairs to the complementary codon on mRNA
- carries the amino acid of the codon it recognizes
anticodon
Bound amino acid
12. Translation: mRNA to protein
1. Ribosomal subunits assemble on mRNA strand
1. Starts at P (pairing) site
2. AUG of mRNA is matched to tRNA with proper anticodon
3. Another tRNA carrying the 2nd amino acid arrives
13. Translation: mRNA to protein
4. The second codon pairs with the anticodon of 2nd tRNA
5. A peptide bond forms between the amino acids
6. Ribosome moves, opening up space for another tRNA
14. Translation: mRNA to protein
7. The ribosome reaches a stop codon,
releases polypeptide
9. Last tRNA is released; ribosome
subunits dissociate; new protein!
Stop codons do not have tRNA
15. Regulating Gene Expression
Transcription and translation are steps in gene expression
(DNA functional protein)
• Are all genes expressed all the time?
• No
• How does the cell “decide” when to express proteins?
Constitutive genes = not regulated so have constantly
expressed protein products (~60-80% of genes)
• Other genes are regulated by control mechanisms
• Things like the cytoskeleton are needed all the time, so the
genes are always turned on and expressed
17. Repression
• inhibits gene expression by action of a repressor
- Blocks RNA polymerase from initiating
transcription
• Usually a response to buildup of a product of a
metabolic pathway decreases synthesis of the
enzyme producing the product
Example: E. coli trp operon
• Requires a corepressor (Tryptophan)
19. When
tryptophan is
abundant
RNA polymerase
Corepressor has to bind to repressor to change its shape to make it functional
Repressors are always there (constituent), but are not turned on/off until something acts on it
20. Induction
• turns on transcription of a gene by an inducer
- Binds the repressor and keeps it from blocking
transcription
ends repression on synthesis of the enzyme
needed for metabolism of a particular substrate
Ex) E. coli beta-galactosidase (Lac operon)
• Inducer = lactose or allolactose (analog)
23. Mutation
Mutation = A change in the base sequence of DNA
• may be neutral, beneficial, or harmful
• Provides genetic variation for natural selection
Mutagen = Agent that causes mutations
Spontaneous mutations: Occur in the absence of a
mutagen
24. Types of Mutations in DNA
• Base substitution (point mutation) - Change in
one base, replaced with a different base
• Missense - Result in change in amino acid
• Nonsense – A base substitution, which results
in a stop codon
• Frameshift - Insertion or deletion of one or more
nucleotide pairs
25. Figure 8.30a, b
Transposons
Transposons = “jumping jeans” segments of DNA that can
move from one region of DNA to another
- Contain insertion sequences for cutting and resealing
DNA
- Complex transposons carry other genes
- Stuck between inverted repeats
26. Bacterial Gene Transfer: Conjugation
Conjugation = transfer of genetic material from one bacterial
cell to another in the form of a plasmid
Plasmid = circular piece of DNA that replicates independently
from the chromosomes
Requires direct cell-to-cell contact:
Sex pilus = projection from
surface of donor cell that
contacts surface of recipient
cell to bring them into contact
F for fertility
27. Example: E. coli fertility (F) factor plasmid
Donor (F+) cell carrying the plasmid transfers the plasmid
to a recipient (F-), which becomes F+
Importance: acquired DNA by recipient adds a new
function, like antibiotic resistance, etc.
Plasmid is replicated through rolling circle replication
28. Antibiotic Resistance
• Misuse of antibiotics selects for resistance mutants
- This can happen from:
• Using outdated or weakened antibiotics
• Using antibiotics for the common cold and other
inappropriate conditions
• Using antibiotics in animal feed
• Failing to complete the prescribed regimen
• Using someone else's leftover prescription
