Learning Objectives Week 6
http://www.biotopics.co.uk/genes/trans.html transcription and translation site from info below
** http://www.youtube.com/watch?v=WsofH466lqk transcription vid
**http://www.youtube.com/watch?v=5bLEDd-PSTQ translation vid
** http://www.youtube.com/watch?v=8nQH0GqFn6k protein synthesis (transcription and translation)
During translation, the following stages are taking place:
(1) Messenger RNA strand passes through ribosome
(2) Triplet CCC codes for the next amino acid to be brought into position in the ribosome
(3) Transfer RNA brings in the appropriate amino acid (proline)
(4) Amino acid added to polypeptide chain
(5) Transfer RNA released to pick up amino acid to be recycled
(6) "Used" messenger RNA strand may pass on to another ribosome
(7) Process repeats with next triplet code until:
(8) Triplet UAA causes translation to stop
(9) If it is "long", the polypeptide chain folds into the shape of the final protein
o The 2 strands of the DNA molecule are temporarily split by enzymes
which cause a short part to be copied into a similarly short section of
RNA molecule. The copying is along the same lines as already
explained, (A for T, G for C, C for G) except that a different base
called U (uracil) replaces T (thymine). Also, RNA is only made of a
single strand, and it contains a different sidechain subunit.
o The two strands of DNA - shown here in black and grey - separate
(under the influence of the enzyme RNA polymerase). Messenger RNA -
here red - forms on one - black - strand of DNA. The other strand - grey
- does not take part in the process.
o The strand of messenger RNA (mRNA) formed then leaves the nucleus
and passes into the cytoplasm. The opened-up section of DNA re-forms
into a double helix, as before. Describe the structure and function of ribosomes.
A ribosome is made of two pieces (subunits). These two subunits are named
according to their ability to sediment on a special gel (the Svedberg unit, a
measure of the rate of sedimentation in centrifugation). The bigger the number
given to the subunit the bigger the molecule.
A typical eukaryotic cell ribosome consists of two subunits named 60S (large
subunit) and 40S (small). They make polypeptides.
A ribosome is a complex made up of one or more ribosomal RNAs and large and
small proteins subunit. Ribosomes are made up of about 1/3 proteins and the rest
are ribosomal RNAs.
The subunits of ribosomes are made in the nucleolus of eukaryotes and the
transported to the cytoplasm. The large and small subunits only come together if
they are attached to an mRNA molecule.
Ribosomes are located in the cytoplasm. They are responsible for bringing
together tRNA and mRNA for translation to occur.
Ribosomes in prokaryotes and eukaryotes are very similar, but their differences
are important. Inhibitors like streptomycin can inhibit bacteria ribosomes, while
the eukaryotes ribosomes are unaffected. This difference is key to designing many
antibiotics and medicines.
A ribosome has three sites, or docking stations, for tRNA: the P site, A site, and E
site. The P site is where tRNAs add amino acids to the polypeptide chain. The A
site holds the tRNA that is next in line to add an amino acid, and the E site is the
site from which empty tRNA's exit the ribosome.
Describe the process by which amino acids are added to a growing polypeptide chain.
o Transfer RNA (tRNA) brings in the appropriate amino acid
o Amino acid is added to polypeptide chain.
o Elongation adds an amino acid to the polypeptide chain until a stop codon
terminates translation. Diagram the overall process of transcription and translation.
Describe the major types of mutations, causes of mutations, and potential
consequences. (SEE WRITTEN NOTES)
Mutations involve a physical change to
genetic material that results in the
abnormal encoding of protein sequences.
o Point Mutation
Point Mutation occurs when there is a
substitution of one nucleotide for another.
This type of mutation usually only impacts
one codon in a sequence.
o Silent Mutation
A silent mutation is a type of point
mutation that does not change the amino acid
sequence of the protein. In silent mutation,
a nucleotide mutates to another nucleotide.
However, the new nucleotide also codes to
the original amino acid. This type of
mutation is likely to have little effect on
the protein sequence.
o Frame-shift Mutation
Frame-shift mutation involves the insertion
or deletion of one or more nucleotides from
the sequence. This insertion or deletion results in a
shifting of the nucleotides. This creates
different amino acids in the protein
sequence. Generally, the amino acid sequence
after the insertion or deletion is
Types of mutations within a gene (same as
Substitution-the substitution of one
nucleotide for anther.
Insertion-to insert or add a
Deletion mutations- to delete or remove
Briefly describe and compare the regulatory mechanisms of the lac operon, and
o Lac operon
Protein synthesis is INDUCED (begins) when lactose is present.
o Trp operon
Protein synthesis is REPRESSED (stops) when a high
concentration of tryptophan is present.
o Lac operon
Consists of a promotor, operator, and a cluster of 3 genes (lacZ,
Explain how selective gene expression yields a variety of cell types in multicellular
o Certain genes are activated through mechanisms such as feedback inhibition,
positive feedback and negative feedback. Look up those terms for examples like
the lac operon and the trp operon
Briefly explain how eukaryotic gene expression is controlled by explaining how mRNA
breakdown, initiation of translation, protein activation, and protein breakdown regulate
o mRNA Breakdown
Enzymes in the cytoplasm breakdown the molecules of mRNA and
the timing of when this occurs is a very important factor in
regulating the amounts of various proteins that are produced in the
Long-lived mRNA’s can be translated into many more protein
molecules than short-lived ones.
mRNA in eukaryotes have liftimes of hours or even weeks.
o o Initiation of Translation
The process of translating an mRNA into a polypeptide also offers
opportunities for regulation. Among the molecules involved in
translation are a many proteins that control the start of polypeptide
synthesis. Red bold cells for instance have an inhibitory protein
that prevents translation of hemoglobin mRNA unless the cell has
a supply of heme, the iron containing chemical group essential for
hemoglobin function. By controlling the start of protein synthesis,
cells can avoid wasting energy if the needed components are
o Protein Activation
After translation is complete, some polypeptides require alterations
before they become functional. Post- translational control
mechanisms in eukaryotes often involve cleavage (cutting) of a
polypeptide to yield a smaller final product that is the active
protein, able to carry our specific functions in the organism. In
Figure 11.6, we see the example of the hormone insulin, which is a
protein. Insulin is synthesized in the cells of the pancreas as one
long polypeptide that has no hormonal activity. After translation is
completed the polypeptide folds up, and covalent bonds form
between the sulfur (S) atoms of sulfur-containing amino acids.
Two H atoms are lost as each S-S bond forms, linking together
parts of the polypeptide in a specific way. Finally, a large center
portion is cut away, leaving two shorter chains held together by the
sulfur linkages. The combination of two shorter polypeptides is the
form of insulin that functions as a hormone. By controlling the
timing of such protein modifications, the rate of insulin synthesis
can be fine-tuned.
o Protein Breakdown
The final control mechanism operating after translation is the
selective breakdown of proteins. Some of the proteins that trigger
metabolic changes in cells are broken down within a few minutes
or hours. This regulation allows a cell to adjust the kinds and
amounts of its proteins in response to changes in its environment.
It also enables the cell to maintain its proteins in prime working
order. When proteins are damaged they are usually broken down
right away and replaced by new ones that function properly.
Describe the basic tools used in biotechnology. Define recombinant DNA, PCR and transgenic organisms.
Describe the basic tools used in biotechnology. Define recombinant DNA, PCR
and transgenic organisms.
o Explain how plasmids are used in gene cloning including the purpose of
restriction enzymes. To manipulate genes in the laboratory, biologists often use bacterial
plasmids, which are small, circular DNA molecules that replicate (
duplicate) separately from the much larger bacterial chromosome ( see
Module 10.23). Because plasmids can carry virtually any gene and are
passed from one generation of bacteria to the next, they are key tools
for gene cloning, the production of multiple identical copies of a gene-
carrying piece of DNA. Gene- cloning methods are central to the m mn
production of useful products via genetic engineering.
1- a bacterial plasmid that will serve as the vector, or gene carrier, and
2- the DNA containing the gene of interest— in this case, gene V (
shown in red in the figure)— along with other, unwanted genes. Often,
the plasmid comes from the bacterium E. coli. The DNA containing gene
V could come from a variety of sources, such as a different bacterium, a
plant, a nonhuman animal, or even human tissue cells growing in
laboratory culture. The researcher treats both the plasmid and the gene
V source DNA with an enzyme that cuts DNA.
3- An enzyme is chosen that cleaves the plasmid in only one place.
4- The other DNA, which is usually much longer in sequence, may be cut
into many fragments, one of which carries gene V. The figure shows the
processing of just one DNA fragment and one plasmid, but actually,