Chapter 17/chapter 18 Dr. Alaie
● Gene expression ² transcription of DNA into RNA.
○ We do not change the language of nucleotides. (It is still the language of
nucleotides )
○ You go from DNA to RNA
○ Transcription is what you see here,
you see a piece of a helix, then you transcribe a portion of the helix, then you get
a single-stranded RNA molecule that is complementary to one of the two DNA
strands² this is called gene expression.
○ gene expression² getting expression from a particular piece of DNA.
○ Depending on the type of RNA, we may translate it / we may never translate it
and used it in its RNA formed.
○ The minute you transcribe a piece of DNA to RNA, you call that a gene
● Translation² When the language of nucleotides is turned into the language of amino
acids (Translating to a different language)
Prokaryotes and eukaryotes
● Prokaryotes and eukaryotes regulate gene expression in response to environmental
conditions.
○ We have to be adaptable and flexible, it is not always have the same stretches of
DNA, the same genes on all the the time
○ Indeed what makes one cell different from another cell is the collection of
proteins that it expresses (the collection of proteins that it has carrying out its
function)
■ Cuz the DNA is the same if you’re looking in the nucleus in our body cell
■ There are some immune cell that has not the same DNA cuz it has been
alter.
■ What makes a stomach cell different than a kidney cell is that certain
genes in the kidney cell are express and not express in stomach cell vice
versa
● There are genes that expressed in different type of cell called
housekeeping genes. For example, (every cell is going to need
all the enzymes that are involved in glacolysis, proteins that make
up the cytoskeleton)
Prokaryotes
● Natural selection has favored bacteria that produce only the gene products needed by
that cell at that particular cell
, ○ This doesn’t mean that same cell can’t shut those off at another time when
they’re not needed and turn it back on later on
○ There’s flexibility/adaptable, so why waste the energy to produce these protein
are not needed at that time
● One mechanism for control of gene expression in bacteria is the operon model
(coordinate control gene, only bacteria do this, human do not do this cuz we
control our genes separately)
○ Prokaryotes do coordinate control gene² where they are going to be putting a
whole bunch of genes under the same control. (like a light switch)
■ Cell wants to do this cuz if the genes that are under the same control are
involved in the same process or genes that are related (either turn all on
or all off)
■ Also it is more efficient and faster speed
● But a different process gene will not be under the same control.
(similar to the idea that you will not put the basement light and
upstair light under the same control cuz you do not need it until
you go down stair, but you will put adjacent room under the same
switch)
Operon
● Operon: A cluster of functionally related genes can be corrdinaely controlled by single
<on-off switch= (like a master light)
● An operon is the entire stretch of DNA that includes the operator, the promoter, and the
genes (they are going to be transcribe) that they control
○ Operator and promoter are control area (the light switch) and they are going to
control genes that function similarly.
■ Operator are exclusive to Prokaryotes cells
● Repressible operon: one that is usually on; binding of a repressor to the operator shuts
off transcription (one that can be repress)
○ The genes are being express, so you have to repress them or turned them off
when yo bind something to it. (bacteria can adapt to something and turned them
are)
○ By default, the trp operon is on and the genes for tryptophan synthesis are
transcribed
■ It is call trp operon because it is the the enzymes that are involve in
making amino acid² trytophan
, ■
■ (Bacteria needs to make tryptophan all the time, they constantly need the
scouce of tryptophan all the time)
■ There are five genes that make up the enzymes 1, 2, 3
● If you look at the picture² Enzyme 1 and 3 looks like it has two
different shape that emerge together cuz there are two
independent polypitide (trp B and trp A) that make up enzyme 3 (
trp E and trp D ² enzyme 1).
○ This mean that there are two genes that code for these two
polypitide, they come together in a coordinary structure to
make up enzyme 1.
○ Trp C just codes for 1 poplypeitide to make ENZYME 2
■ trpE +trp D= enzyme 1
■ Trp C= enzyme 2
■ Trp B +trp A = enzyme 3
○ This is the biosynthetic pathway that lead to
the amino acid ² trptophan. YOU need all three enzyme.
■ The precursor are done by enzyme 1, the product
is the substrate for ezyme 2, etc. Enzyme 3 then is
able to generate tryptophan.
● Gene expression ² transcription of DNA into RNA.
○ We do not change the language of nucleotides. (It is still the language of
nucleotides )
○ You go from DNA to RNA
○ Transcription is what you see here,
you see a piece of a helix, then you transcribe a portion of the helix, then you get
a single-stranded RNA molecule that is complementary to one of the two DNA
strands² this is called gene expression.
○ gene expression² getting expression from a particular piece of DNA.
○ Depending on the type of RNA, we may translate it / we may never translate it
and used it in its RNA formed.
○ The minute you transcribe a piece of DNA to RNA, you call that a gene
● Translation² When the language of nucleotides is turned into the language of amino
acids (Translating to a different language)
Prokaryotes and eukaryotes
● Prokaryotes and eukaryotes regulate gene expression in response to environmental
conditions.
○ We have to be adaptable and flexible, it is not always have the same stretches of
DNA, the same genes on all the the time
○ Indeed what makes one cell different from another cell is the collection of
proteins that it expresses (the collection of proteins that it has carrying out its
function)
■ Cuz the DNA is the same if you’re looking in the nucleus in our body cell
■ There are some immune cell that has not the same DNA cuz it has been
alter.
■ What makes a stomach cell different than a kidney cell is that certain
genes in the kidney cell are express and not express in stomach cell vice
versa
● There are genes that expressed in different type of cell called
housekeeping genes. For example, (every cell is going to need
all the enzymes that are involved in glacolysis, proteins that make
up the cytoskeleton)
Prokaryotes
● Natural selection has favored bacteria that produce only the gene products needed by
that cell at that particular cell
, ○ This doesn’t mean that same cell can’t shut those off at another time when
they’re not needed and turn it back on later on
○ There’s flexibility/adaptable, so why waste the energy to produce these protein
are not needed at that time
● One mechanism for control of gene expression in bacteria is the operon model
(coordinate control gene, only bacteria do this, human do not do this cuz we
control our genes separately)
○ Prokaryotes do coordinate control gene² where they are going to be putting a
whole bunch of genes under the same control. (like a light switch)
■ Cell wants to do this cuz if the genes that are under the same control are
involved in the same process or genes that are related (either turn all on
or all off)
■ Also it is more efficient and faster speed
● But a different process gene will not be under the same control.
(similar to the idea that you will not put the basement light and
upstair light under the same control cuz you do not need it until
you go down stair, but you will put adjacent room under the same
switch)
Operon
● Operon: A cluster of functionally related genes can be corrdinaely controlled by single
<on-off switch= (like a master light)
● An operon is the entire stretch of DNA that includes the operator, the promoter, and the
genes (they are going to be transcribe) that they control
○ Operator and promoter are control area (the light switch) and they are going to
control genes that function similarly.
■ Operator are exclusive to Prokaryotes cells
● Repressible operon: one that is usually on; binding of a repressor to the operator shuts
off transcription (one that can be repress)
○ The genes are being express, so you have to repress them or turned them off
when yo bind something to it. (bacteria can adapt to something and turned them
are)
○ By default, the trp operon is on and the genes for tryptophan synthesis are
transcribed
■ It is call trp operon because it is the the enzymes that are involve in
making amino acid² trytophan
, ■
■ (Bacteria needs to make tryptophan all the time, they constantly need the
scouce of tryptophan all the time)
■ There are five genes that make up the enzymes 1, 2, 3
● If you look at the picture² Enzyme 1 and 3 looks like it has two
different shape that emerge together cuz there are two
independent polypitide (trp B and trp A) that make up enzyme 3 (
trp E and trp D ² enzyme 1).
○ This mean that there are two genes that code for these two
polypitide, they come together in a coordinary structure to
make up enzyme 1.
○ Trp C just codes for 1 poplypeitide to make ENZYME 2
■ trpE +trp D= enzyme 1
■ Trp C= enzyme 2
■ Trp B +trp A = enzyme 3
○ This is the biosynthetic pathway that lead to
the amino acid ² trptophan. YOU need all three enzyme.
■ The precursor are done by enzyme 1, the product
is the substrate for ezyme 2, etc. Enzyme 3 then is
able to generate tryptophan.
