Chapter 7:
The Blueprint of Life,
from DNA to Protein
Where we’ve been…
• Our bacterium has
–
–
–
–
Entered the host’s body through the Portal of Entry.
Adhered to the host’s cells
Competed with host’s normal microbiota
Successfully defended itself against the host immune
system (more in Stage 03…)
– Found the right environment (pH, temperature, oxygen
requirement, and water availability)
– Found and transported in the right nutrients
– And, finally, through catabolic reactions, harvested
energy and made precursor metabolites that were made
into subunits.
Metabolism
• The sum total of ALL
chemical reactions
within a cell
– Catabolic
– Anabolic
Where we’re going…
• Now we are going to take those subunits
(nucleotides, amino acids, monosaccharides,
glycerol and fatty acids) and put them together
to make macromolecules so we can make
another bacterial cell.
• Nucleotides --> nucleic acids (RNA, DNA)
• Amino acids --> proteins
• Monosaccharides --> polysaccharides
• Glycerol + fatty acids --> lipids
Where we’re going…
• Now we are going to take those subunits
(nucleotides, amino acids, monosaccharides,
glycerol and fatty acids) and put them together
to make macromolecules so we can make
another bacterial cell.
• Nucleotides --> nucleic acids (RNA, DNA)
• Amino acids --> proteins
• Monosaccharides --> polysaccharides
• Glycerol + fatty acids --> lipids
Making macromolecules!
• DNA nucleotide subunits --> DNA Replication to
make DNA.
• RNA nucleotide subunits --> Transcription to
make RNA.
• amino acid subunits --> Translation to make
proteins.
What do you know about DNA?
• Chromosomes made of DNA contain an
organism’s entire genome
• DNA codes for genes….genes code for
proteins
• Chemical composition is nucleotides
• It exists in most cells as a double stranded
structure
DNA Structure
DNA Base Pairing
A-T
G-C
DNA Structure
DNA Base Pairing
A-T
G-C
DNA Replication
Enzymes necessary for DNA
replication: more about enzymes!
• DNA gyrase, Helicase, Primase, DNA polymerase, DNA ligase
http://www.chem4kids.com/files/bio_enzymes.html
From: http://waynesword.palomar.edu/molecu1.htm
Enzymes can break molecules apart
http://www.chem4kids.com/files/bio_enzymes.html
Enzymes can put molecules together
Nucleotides are added to the 3’
position (OH group)
DNA Base Pairing
A-T
G-C
DNA replication…a closer look
DNA polymerase
polymerizes
DNA nucleotides together
in the 5’ -> 3’ direction
to make DNA.
DNA polymerase
requires a primer
(short stretch of nucleotides)
and a template
in order to begin work.
DNA replication…closer look
http://www.youtube.com/watch?v=yqESR7E4b_8
Where we’re going…
• We just put DNA nucleotides together to
make DNA during DNA Replication.
• Now we have to make more proteins needed
to build our new cell.
Gene Expression…why is it
important?
• Transcription
• Translation
In order for our cell to
replicate, it needs to
make the proteins that
are needed to build that
new cell. DNA has the
blueprints (genes) for
making these proteins.
Transcription: RNA is
transcribed from DNA
Comparing bases:
DNA: G, A, T, C
RNA: G, A, U, C
Base Pairing:
DNA-RNA
G-C
A-U
T-A
C-G
Transcription: DNA to RNA
• Requires an enzyme - RNA polymerase
• RNA nucleotides
• Base pairing rules for building RNA from a
DNA template
• Process proceeds in the direction 5’--->3’
• Process begins at the promoter region and
ends at the terminator sequence
Transcription: RNA synthesis
Base Pairing:
DNA-RNA
G-C
A-U
T-A
C-G
Transcription: Promoter orients
direction of transcription
What are the possible products
from transcription?
• Messenger RNA (mRNA)
– Encodes the message for a protein.
• Transfer RNA (tRNA)
– Essential component to translate RNA language into
amino acid language during translation.
• Ribosomal RNA (rRNA)
– Together with protein, this makes up the structure of a
ribosome.
Translation: RNA to protein
• What is needed for the process?
–
–
–
–
mRNA
Amino acids
tRNA
Ribosomes
“Speaks” both
amino acid
language
AND
RNA language!
Able to translate
the RNA code
into amino acids!
Translation: RNA to protein
• What is needed for the process?
–
–
–
–
mRNA
Amino acids
tRNA
Ribosomes
Large
subunit
Small
subunit
• Connects amino acids
together to make a protein!
Prokaryotic ribosome
The Genetic code:
Translating RNA to amino acids
Translation
Translation
Translation: reading frame
determines the protein
Both processes occur at the same
time in bacteria…
…because the DNA is not separated from the ribosomes
(like in eukaryotic cells!)
Is it important to regulate protein
synthesis?
• Yes!
• Genes to produce enzymes for glucose
metabolism are constitutive (always made)
• Other genes are inducible…only made
when needed (lactose operon)
• Other genes are repressible…turned off
when not needed (tryptophan operon)
Models for transcriptional
regulation with repressors
Transcriptional regulation by
activators
Lactose Operon as a model
• Used to understand control of gene
expression in bacteria
• Operon consists of three genes needed to
degrade lactose
• Repressor gene(codes for repressor protein)
outside of operon coding region inhibits
transcription unless something else bind to
the repressor protein
Lactose Operon
Diauxic growth curve of E. coli
What conditions are needed for the lactose
operon to be turned “on”?
• No glucose
• Increasing levels of cAMP
• cAMP binds to CAP, then complex binds next to
lactose operon promoter at the activator region
• RNA polymerase binds to promoter
• Lactose present
• Allolactose binds to repressor, keeping it from
binding to the operator
• RNA polymerase can transcribe the gene
How do organisms adapt to other
changes in their environment?
• Some organisms turn genes on/off as
needed
• Some organisms alter gene expression
Gene regulation systems in bacteria
• Signal transduction
– Two component regulatory
system
• E. coli use this system to
sense if nitrate is present
when in an anaerobic
environment. It turns on
genes to use nitrate as the
terminal electron acceptor
for use in anaerobic
respiration!
Gene regulation systems in bacteria
• Signal transduction
- Quorum sensing
Quorum sensing turns on
biofilm production!
Metabolism
• The sum total of ALL
chemical reactions
within a cell
– Catabolic
– Anabolic
DNA Replication
Transcription
Translation