BIO93 FINAL (CHAPTER 19)

the complex of DNA and proteins that makes up a eukaryotic chromosome; when the cell is not dividing, chromatin exists as a mass of very long, thin fibers that are not visible with a light microscope.

• -regulation of genes expressed at any given time
• -control of gene expression can occur at many different stages in the pathway that lies between transcription of a gene and activity of the protein.
• -the most important and commonly used strategy for regulating gene expression acts at the LEVEL OF TRANSCRIPTION- which genes are copied by the RNA polymerase.

• -regulation of chromatin structure
• -regulation of transcription
• -regulation of RNA processing
• -regulation of translation
• -posttranslational regulation
• -regulation of protein degradation

a small protein with a high proportion of positively charged amino acids that binds to the negatively charged DNA and plays a key role in its chromatin structure.

• -the attachment of acetyl groups to certain amino acids of histone proteins.
• -when histones are acetylated, the positive charges are neutralized and histone tails no longer bind to neighboring nucleosomes.
• -this unfolding allows the transcription proteins to have greater access to the DNA to initiate TRANSCRIPTION.

• (1) heterochromatin (tightly compacted form)
• (2) euchromatin (less compacted form)

non-transcribed eukaryotic chromatin that is so highly compacted that it is visible with a light microscope during interphase.

the more open, unraveled form of eukaryotic chromatin that is available for transcription.

When the DNA is more compacted, the transcriptional machinery cannot access the DNA & therefore transcription is not active for the genes in that region.

• -regulation of transcription is needed for the cell to quickly adapt to the ever-changing outer environment.
• -done by a cluster of functionally related genes that can be under coordinated control by a single on-off switch.
• -the regulatory switch is a segment of DNA called the OPERATOR, usually positioned with the PROMOTER.
• -an OPERON is the entire stretch of DNA that includes the operator, the promoter, and the genes they control.

the segment of DNA that acts as a regulatory switch

the entire stretch of DNA that includes the OPERATOR, PROMOTER, and the genes they control.

• -requires galactoside permease which allows lactose to enter the cell.
• -requires B-galactosidase to catalyze the hydrolysis of lactose to galactose and glucose.
• -E. coli can then use glucose via glycolysis.
• -converts galactose to glucose via glycolysis.
• -when lactose is present, the repressor becomes inactivated and the lac operon is allowed to be transcribed.

• (1) core promoter (not a control element); leads to basal levels of transcription.
• (2) PROXIMAL CONTROL ELEMENTS; located close to the core promoter; activators & repressors can bind.
• (3) DISTAL CONTROL ELEMENTS; necessary for full activation/repression.

protein that binds to an enhancer and stimulates transcription of a gene.

• -distal control elements
• -DNA segment containing multiple control elements that may be located far way from the gene it regulates.

• (1) ACTIVATORS BIND ENHANCERS
• (2) DNA BENDS
• (3) ACTIVATORS STABILIZE TRANSCRIPTION COMPLEX

• (1) DNA BINDING DOMAIN (DBD): allows protein to bind to specific DNA sequences.
• (2) ACTIVATION DOMAIN: allows protein to stabilize transcription initiation complex.

alternate splicing generates different proteins from the same gene.

a portion of a DNA or primary transcript sequence that DOES NOT CODE FOR PROTEIN.

because different genes are switched on and off in each type of cell.

• -a gene found in viruses or as part of the normal genome that is involved in triggered cancerous characteristics.
• -GAIN-OF-FUNCTION MUTATIONS

• -mutations that change the gene product such that it gains a new and abnormal function.
• -these mutations usually have dominant phenotypes; only need one copy of the mutated gene to produce excessive cell division
• -DOMINANT MUTATION
• -GROWTH-STIMULATING PATHWAY IS ENHANCED.

normal cellular genes that code for proteins that stimulate normal cell growth.

MUTATIONS that alter genes that normally regulate cell growth and division during the cell cycle include genes for growth factors, their receptors, and the intracellular molecules of signaling pathways.

• -CELL CYCLE-STIMULATING PATHWAY.
• -CELL CYCLE-INHIBITING PATHWAY.
• -EFFECTS OF MUTATIONS.

an oncogene arises from a genetic change that leads to an increase either in the amount of the proto-oncogenes protein product or in the instrinsic activity of each protein molecule.

• (1) movement of DNA within the genome.
• (2) amplification of a proto-oncogene.
• (3) point mutations in a control element or in the proto-oncogene itself.

• -in the promoter or enhancer that controls a proto-oncogene, causing an increase in its expression
• -in the coding sequence, changing the gene's product to a protein that is more active or more resistant to degradation that the normal protein.

• -G protein that relays a signal from a growth factor receptor on the plasma membrane to a cascade of protein kinases.
• -if Ras has been activated, cells will begin to divide rapidly.

• -gene whose protein products inhibit cell division, thereby preventing uncontrolled cell growth (cancer).
• -LOSS-OF-FUNCTION MUTATIONS

• -mutations that are the result of gene product having less or no function.
• -RECESSIVE MUTATION (still work as long as there is one good copy of the gene).
• -GROWTH INHIBITING PATHWAY FAIL.

• -tumor-suppressor gene.
• -encodes for tumor suppressor protein.
• -example of defective tumor suppressor gene.
• -example of LOSS-OF-FUNCTION MUTATION.
• -SPECIFIC TRANSCRIPTION FACTOR THAT PROMOTES SYNTHESIS OF CELL CYCLE-INHIBITING PROTEINS.
• -mutations that KNOCK OUT the p53 gene can lead to excessive cell growth and cancer.

cancer always entails unrestrained cell division.