Molecular Biology Lecture Quiz 4

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Transcription

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Synthesis of RNA using a DNA template (DNA making copies of RNA).

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Translation

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Synthesis of a protein using genetic information encoded in a mRNA molecule (translating nucleic acids into amino acids).

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P site

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Holds the tRNA carrying the growing polypeptide chain (protein).

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A site

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Holds the tRNA carrying the next amino acid to be added to the growing chain.

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E site

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Site from which empty tRNA’s exit.

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Stage 1: Initiation

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The initiator tRNA waits in the P site for the next tRNA to occupy the A site.

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Stage 2: Elongation

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The tRNA in the P site is translocated to the E site and released while the tRNA in the A site is translocated to the P site.

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Stage 3: Termination

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Release factor promotes hydrolysis of the bond between tRNA in the P site and the last amino acid of the polypeptide.

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mRNA degradation in prokaryotes

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Bacterial mRNA molecules are degraded by enzymes within a few minutes of their synthesis.

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mRNA Degradation eukaryotes

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mRNA molecules in multicellular eukaryotes typically survive for hours, days, or even weeks.

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Protein Processing and Degradation

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i. Process proteins for functional protein molecules.
ii. Add phosphate groups to in/activate proteins.
iii. Add sugars to in/activate cell surface proteins.
iv. Transport proteins to target destinations in order to function.

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proteasomes

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Giant protein complex that recognizes and destroys proteins tagged for elimination by the smaller protein ubiquitin.
i. Regulates the length of time each protein functions.
ii. Example: cyclins during cell cycle = short-lived.

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Multistep Model of Cancer Development

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1. Loss of tumor suppressor gene APC
2. Activation of the ras oncogene
3. Loss of tumor suppressor gene DCC
4. Loss of tumor suppressor gene p53
5. Additional mutations

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Bacteriophages

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i. Most complex capsids.
ii. Elongated icosahedral heads with DNA.
iii. Protein tailpiece with fibers for attachment to a bacterium.

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Lytic cycle

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Replicative cycle resulting in the release of new phages by lysis (and death) of the host cell.

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Lysogenic cycle

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Replicative cycle in which the viral genome becomes incorporated into the bacterial host chromosome, replicating with the chromosome without killing the host.

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Pathways of Emerging Viruses

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Step #1: Mutation of existing viruses.
Step #2: Dissemination of viral diseases from small, isolated human populations.
Step #3: Spread of existing viruses from other animals which become sources of new diseases in humans.

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Basic structure of a bacterium

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1. Nucleoid
2. Cytoplasm and ribosomes
3. Cytoplasmic membrane
4. Cell wall
5. Capsule
6. Pili
7. Flagella

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Gram Positive

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Structurally less complex cell walls with more
peptidoglycans (traps crystal violet); usually less toxic.
Tend to be less resistant to antibiotics due to simpler cell wall (antibiotics inhibit cell wall function by interfering with its construction).

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Gram Negative

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Structurally more complex cell walls with less
peptidoglycans (loses crystal violet); usually more toxic.
Tend to be more resistant to antibiotics due to more
complex cell wall (lipid portions tend to be toxic causing fever or shock).

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Archaea

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Extremophiles
Thermophiles
Halophiles
Methanogens

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Extremophiles

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Organisms that live in environmental conditions so extreme that few other spp can survive there.

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Thermophiles

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Organism that lives in hot environments (60 - 80°C or higher). DNA and proteins do not denature.

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Halophiles

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Organism that lives in a highly saline environment
Compensate for water loss by pumping K ions into the cell until an isotonic concentration is reached between the cell and its environment.

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Methanogens

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Organisms that produce methane as a waste product of the way it obtains energy.
i. Found in swamps and marshes.
ii. Found in guts of herbivores.
iii. Poisoned by oxygen.