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Translation (written lesson)
Q: How are proteins (amino acid chains) made from the information in
mRNA?
A: Translation
Ribosomes translate mRNA into protein
Translation has 3 steps also!
1.
Translation Initiation: mRNA binds to a ribosome and a
tRNA binds to the ribosome, bringing in the first amino acid
(a.a.)
2.
Translation Elongation: Ribosome covalently links a.a.'s
together as additional tRNA's bring them to the ribosome in
response to the message of the mRNA.
3.
Translation Termination: When the "stop codon" of the
mRNA gets to the ribosome, translation stops. mRNA is
released from the ribosome; tRNA is released; newly
synthesized protein is released.
How does the mRNA sequence of nucleotides direct a ribosome to connect
the proper protein sequence of amino acids???
The genetic code = the way that the 4 bases of RNA encode the amino acid
sequence of protein.
Proteins are made of monomers called amino acids. There are 20 different
amino acids. Each protein is made of a different combination of a.a.'s.
A messenger RNA is actually a code language that tells the ribosomes which
amino acid to add first, second, third, etc. in the protein chain. The "code
words" of mRNA are called codons.
3 nucleotides specify one amino acid = a codon
*AUG does code for an amino acid, Methianine, therefore "Met" is
always the first amino acid in a protein.

What is tRNA and what is its role in translation?
 tRNA's carry amino acids (a.a.'s) to the ribosome during translation; the
ribosome then links the a.a.'s together into a peptide chain.
 tRNA is a single-stranded RNA molecule the folds on itself through Hbonds between internally complementary nucleotides. Once it has folded,


a tRNA is shaped like a cloverleaf.
There are many different tRNA's. They are all similar to one another in
their cloverleaf shape, but each one carries a different a.a.
Each tRNA has an "anti-codon" that is complementary to a specific codon
of mRNA. The a.a. that a tRNA carries corresponds to the codon that its
own anti-codon recognizes. e.g. A tRNA whose anti-codon is AAG will
carry the a.a. “Phenylalanine/Phe” because AAG is complementary to the
codon UUC, which is a codon for Phe (see genetic code chart above.)
5’
NH2
GAC
CUG
CUG
GAC
3’
AMINO ACID =
ASPARTATE
AMINO ACID =
LEUCINE
What is the structure of the ribosome? How does a ribosome build
proteins?
 The intact ribosome is actually a combination of two subunits. The two
subunits are named the "small subunit" and the "large subunit" and they
must come together before translation can begin.
 Ribosome subunits are made of 1) ribosomal RNA (rRNA) and 2) many
different proteins. Together, the rRNA's and the proteins of a
ribosome's subunits act as a huge enzyme complex that can create
proteins by forming new peptide bonds between a.a.'s.
 Every intact ribosome has three important active sites: 1) mRNA-binding
site, 2) tRNA-binding site #1 (also called the "P" site) 3) another tRNAbinding site, #2 (also called the "A" site.)
How does the ribosome work with the tRNA's and with the mRNA to
elongate a chain of amino acids?
Please see cartoon!!!
1.
INITIATION
Of
TRANSLATION
2.
3.
mRNA binds to the small subunit of a ribosome,
then the 1st transfer RNA (always carries
methionine) binds to the #1 binding site of the
ribosome and to mRNA's start codon
large subunit joins the complex
A second tRNA binds to the ribosome's #2 site and
to the second codon of the mRNA. (The second
tRNA is chosen by its anti-codon (because its anticodon is complementary to the codon of the
mRNA.))
Initiation of Translation:
Amino Acids
m-RNA
t-RNA’s
START CODON
5’
Initiation
Complex
P Site
Small Subunit
of Ribosome
A Site
Large Subunit
of Ribosome
3’
ELONGATION
Of
TRANSLATION
The ribosome catalyzes a reaction: the two amino
acids carried in by the two tRNA's are linked by
a peptide bond.
4.
The 1st tRNA is released, but the amino
acid that it carried is now covalently
linked to the second tRNA's amino acid.
5.
The ribosome moves tRNA #2 over into
tRNA-binding site #1. This leaves
tRNA-binding site #2 open for a third
tRNA to bind. The shift of tRNA #2
also pulls the mRNA further into the
ribosome.
6.
tRNA's continue to deliver a.a.'s to the
ribosome, and the ribosome continues to
covalently link the amino acids by
forming peptide bonds between them.
Each time an amino acid is added to the
growing chain, the ribosome shifts the
tRNA that was in binding site #2 over
into site #1, pulling the mRNA in a little
and exposing site #2.
Elongation Phase of Translation:
Amino Acids
t-RNA’s
5’
New Protein
NH2
3’
TERMINATION
Of
TRANSLATION
7.
When a stop codon is reached, the newly
formed protein chain is released by the
ribosome. The last tRNA is released by
the ribosome. The two subunits of the
ribosome fall apart. The mRNA is
released by the ribosome.
Amino Acids
t-RNA’s
5’
3’
New Protein
STOP CODON
NH2
Amino Acids
t-RNA’s
m-RNA
COOH
5’
New Protein
NH2
End of Translation Lesson
3’
REPLICATION (written lesson with still pictures)
How is the double helix/DNA replicated (during the S phase of interphase)?
The two strands of the parent DNA are antiparallel. This means that
the 5’ end of one strand pairs with the 3’ end of the opposing strand.
Adenine Hydrogen bonds to Thymine and Guanine H-Bonds to Cytosine.
Thus we say that A and T are complementary and G and C are
complementary.
Steps in DNA replication (synthesis):
1.
Parental (double-stranded) DNA molecule unwinds and
hydrogen bonds between complementary pairs are broken leaving
two separated, complementary backbones. The enzyme that
performs the unwinding and separation is called DNA Helicase.
This enzyme gradually "unzips" the two strands of the parent
molecule.
5’ A
G
C
A
T
T
A
G
C
C
G
A
T
A
T
T
3’
G
G
T 3’
DNA Helicase Enzyme
T
A
A
C
C
5’
2.
Once the two parent strands have been separated by
Helicase, new complementary strands are made, using the singlestranded parent strands as templates.
The enzyme that performs the synthesis of new, complementary strands is
DNA Polymerase. (Creates a polymer from monomers)
5’ A
G
C
A
A
T
T 3’
G
C
A
T
T
A
DNA Polymerase
Enzymes
C
G
T
T
A
A
T
3’
G
G
C
C
5’
Limitations of DNA Polymerase:
1) DNA Polymerase can only add free complementary nucleotides to parental
strand's 3' end. Since the strands of DNA are anti-parallel, when Helicase
opens the molecule one single-stranded parent has a free 3' end, but the
other has a free 5' end. Only the parent whose 3' end is single-stranded will
be copied continuously by DNA Polymerase. This strand is called the Leading
Strand. DNA Polymerase simply binds to the open 3' end and adds
complementary bases along toward the branch point. The other parent
strand must be copied in short, discontinuous pieces; therefore, it is called
the lagging strand. DNA polymerase "waits" for helicase to unzip an entire
segment of the double helix, it binds to the lagging strand at the branch
point, which is its 3' end, and adds nucleotides away from the branch point.
This creates a short fragment of daughter strand. Then the enzyme waits
for another segment of lagging strand to be exposed by Helicase, and then it
binds near the branch point and adds nucleotides down toward the small
fragment it previously created.
5’ A
G
T 3’
On the “Leading Strand”
DNA Polymerase
continuously adds new
nucleotides, as it
follows DNA Helicase
C
T
A
T
T
A
G
C
C
C
G
G
A
T
A
T
T
A
T
A
G
3’ G
C
C 5’
A
On the “Lagging Strand”
5’
DNA Polymerase
runs in the opposite
direction of the Helicase,
and therefore must make
a series of discontinuous
pieces (or fragments).
A
T
A
T
T
A
T
A
G
3’ G
C
C 5’
A
T 3’
C
G
C
A
T
A
T
T
A
T
A
G
C
C
C
G
G
A
T
5’ A
T
A
T
A
T
T
A
T
A
T
A
T
A
5’ A
T
G
G
3’ G
C
C 5
5
G
3’ G
C
C
5’
2) The second limitation of DNA Polymerase is that it
cannot form a covalent bond between the fragments it
has created on the lagging strand. The enzyme that
does connect the fragments is called DNA Ligase.
5’ A
5
T 3’
A
T 3’
G
C
G
C
A
T
A
T
T
A
T
A
G
C
G
C
C
G
C
G
A
T
5’ A
T
A
T
A
T
T
A
T
A
T
A
T
A
G
3’ G
C
C 5
DNA Ligase enzyme
can connect the two
fragments by forming
a covalent bond
between them.
3’
G
3’ G
C
C 5’
Since the two strands of the parent molecule were
complementary, and since the two new strands are complementary
to the parent, the two, double-stranded daughter molecules are
identical to each other and to the original/parent DNA molecule.
They are called sister chromatids.
5’ A
5’ A
T 3’
T 3’
G
C
G
C
A
T
A
T
T
A
T
A
G
C
G
C
C
G
C
G
A
T
A
T
A
T
A
T
T
A
T
A
T
A
T
A
C
G
3’ G
G
3’ G
We now have two
identical daughter
molecules of DNA,
and the cell is ready for
a Mitosis or a Meiosis
division.
C 5
End of Replication Lesson
C
C 5’
Electron Transport in the Mitochondria (Written Lesson)
Most of the cell’s ATP is generated by a process called
chemiosmosis or oxidative phosphorylation which occurs as a
result of electron transport in the mitochondria.
IV. Electron Transport Chain/System (ETS) and Chemiosmosis
1. occurs in/across the inner membrane of the mitochondria
The Mitochondria up
Inner
Outer Membrane
Matri
Inter Membrane
Compartment
2. high energy electrons from NADH or FADH2 are
transferred from one membrane-bound protein to the
next
H+
H+
H+
H+
H+
e
When NADH gives up its
high-energy electrons, it also
loses an H+; this reaction also
produces NAD+.
-
NADH
NAD+ + H+
The high-energy electrons
are automatically passed (one
electron at a time) from
one protein to the next.
3. at each pass... the electron becomes more stable, and a
little bit of its high energy is released
4. that released energy is used to create an H+ ion gradient
(forcing H+ ions into an area of high concentration by
active transport)
H+
H+
H+
H+
H+
H+
H+
e-
H+
Each time the electron is
passed, some of its energy is
used for the active transport
of H+ into the inter-membrane
Space.
5. the H+ ions build up in the inter-membrane compartment
(between the two mitochondrial membranes)
6. Another membrane-bound protein/enzyme named ATP
Synthase is used as a channel through which the protons
can flow down their gradient and back into the matrix.
7. When the H+ ions flow down their gradient, they release
Energy. That released energy is used by the ATP
Synthase to phophorylate (add a third phosphate group
to) ADP, producing ATP.
H+
H+
H+
H+
H+
H+
2
As the H+ ions flow through the
ADP + Pi
ATP Synthase, they release
energy. This energy is used by
the ATP Synthase to produce
ATP.
ATP
H+
H+
8. At the end of the electron transport chain, the final
electron acceptor is oxygen gas, O2, and when O2 is
reduced by accepting electrons, it also picks up Hydrogen
atoms, becoming H2O.
H+
H+
H+
H+
H+
H+
e
The final electron acceptor is O2
(Oxygen gas). O2 accepts the
electron as it releases the last of its
energy. The O2 also picks up H+
creating H2O.
-
O2
H2
H+
End of Electron Transport in Cellular Respiration Lesson
O
The Light Reactions of Photosynthesis (Written Lesson)
The light reactions of photosynthesis occur in the thylakoid
membrane of the chloroplast. Sunlight energy is absorbed by
photosystems which are collections of chlorophyll pigment
molecules embedded in the thylakoid membrane. There are two
types of photosystem in the thylakoid membrane; Photosystem I
and Photosystem II.
The Chloroplast up Close
Inner
Outer
Strom
Inter Membrane
Compartment
Thylakoid Membrane
Stroma
The chloraphyll pigment
molecules that are capable of
capturing sunlight energy
are clustered together in the
Thylakoid Membrane.
These clusters are called
photosystems. This
cluster is Photosystem II.
Thylakoid Membrane
II
Thylakoid space
Photosystem II (only called II because it was the second of the
two to be understood)
1. the chlorophyll absorbs the energy from sunlight
2. the reaction center (a single chlorophyll) collects
all the energy from surrounding chlorophyll
molecules
3. two of the electrons of the reaction center
chlorophyll absorb so much energy that they leave
the chlorophyll altogether
Stroma
One of the reaction center’s
electrons becomes so
energetic that it jumps off the
photosystem and onto
the first carrier, and then is
passed along horizontally by
redox reactions.
e
-
II
Thylakoid space
4. because the chlorophyll does not like losing
electrons, it requires a replacement for it's lost
electron... the replacement electron is produced by
the splitting of one molecule of H2O (this is the
step that produces oxygen gas)
Stroma
When water splits three products
are formed:
1) O2 (this is the step where plants
generate Oxygen gas)
+
2) H ions
•
Electrons that are immediately
used to replace the reaction
center’s lost electron.
eII 2e1/2O2
H2O
H+ H+
H+
H+
Thylakoid space
H+
H+
5. the excited electron from chlorophyll is accepted
by a protein of the electron transport system
6. the same type of chemiosmosis that occurs in
mitochondria also occurs in the thylakoid disc to
produce ATP. Except here the Thylakoid
Compartment is the Reservoir for H+ ions.
Stroma
H+
As Photosystem II’s electron
is passed along,
it moves to carriers with
higher and higher redox
potentials (more electronegative).
Therefore these redox reactions
release energy. This energy
is used to actively transport
H+ ions into the thylakoid
space.
eII
H+
H+ H+
Thylakoid space
H+
H+
Strom
In the Chloroplast, the H+ ions
flow down their gradient into the
stroma, releasing energy as they
go. This energy is used to drive
synthesis of ATP.
ATP
H+
ADP + Pi
eI
H+
H+ H+
Thylakoid
H+
7. the final electron acceptor of Photosystem II is
the reaction center chlorophyll in Photosystem I
*In Photosystem I electrons are also excited by sunlight. An
excited electron from Photosystem I is ultimately passed to
NADP+ which also accepts 2 electrons and 1 H+ ion to form
NADPH. Thus NADP+ is the final electron acceptor.
In Photosystem I’s high energy
electron is NOT
used as an energy source to pump
H+. Rather, it is passed to the
“High-energy Electron Carrier”
NADP+, which also picks up
H+, generating NADPH.
Stroma
NADP+ + H+
NADP
H
e
-
II
I
e
-
H+
H+ H+
Thylakoid space
H+
H+
*The differences between Photosystem I and II are that the
arrangement of the chlorophylls is different, and their
associated electron transport systems are different
*The main product that comes from Photosystem II is ATP
from Photosystem I is NADPH
This ATP and NADPH will be used to power the reactions of the
Calvin Cycle, the pathway where glucose is made.