Cell and Molec Final Exam

ronisopa's version from 2016-12-06 23:28

Section 1

Question Answer
Replication ForksPoints where a pair of replicating segments of DNA come together and join the nonreplicated segments
Where does replication start?Starts at the origin site
DNA polymeraseIs responsible for syntehsizing new DNA strands from a template. Moves in 3' to 5' direction. Uses an RNA primer
PrimaseAn RNA polymerase that assembles an RNA primer on the 5' end of both strands
Helicaseunwinds the parental strand
PrimosomePrimase and helicase
Beta ClampHelps the DNA pol to move processively.
Exonuclease Activity5' to 3" end cuts off the primers. 3' to 5' end proofreading.
RepliconsEukaryotes replicate their genome in small portions. Each has its own origin from which replication forks proceed outward bidirectionally.

Section 2

Question Answer
Nuclotide Excision RepairRemoves bulky lesions. Transcription coupled path or global genomic path. Damage recognized by protein, the strand is separated. An incision by a pair of enonucleases, excision and then repair synthesis.
Base Excision RepairRemoves altered nucleotide. Recognition of alteration by glycosylase, cleavage of glycosidic bond holding base to sugar. Endonuclease cleaves DNA backbone, sugar-phosphate remnant removed by DNA pol and filled in. Sealed by DNA ligase.
Double-Strand Breakage RepairIonizing radiation. Nonhomologous end joining and homologous recombination. Repairing by NHEJ. Lesion detected. Protein ku binds to broken ends and recruits DNA-PKcs. DNA ends brought together and joined by DNA ligase 4
Mismatch repairThe correction of mistakes that escape the DNA pol proofreading activity.

Section 3

Question Answer
Maturation Promoting FactorMPF consists of two subunits: a kinase and a regulatory subunit, cyclin. Increased cyclin concentration activates the kinase. Cyclin levels fluctuate predictably.
Cyclin BindingCyclin binds to the catalytic subunit of Cdk. Cycin-Cdk complexes phophorylate and thereby regulate other proteins involved in cell division.
Phosphorylation and dephosphorylation of CDKCAK phosphorylates a Thr on CDK subunit that activates. Wee1 phosphorylates Tyr residue that inactivates CDK until it is the proper size. The single Thr drives the cell into mitosis
Controlled ProteolysisOccurs via the ubiquitin-proteasome pathway. Destruction of the mitotic cyclins allows a cell to exit mitosis. Degradation of of CDK inhibitor Sic1 and enable entry into S-phase.
ProphaseDuplicated chromosomes are prepared for segregation and the mitotic machinery is assembled.
Formation of the Mitotic SpindleThe centrosome is a MT- organizing structure. Contains the centrioles and surrounded by pericentriolar material. The Mitotic spindle is made of MT
PrometaphaseMitotic spindle is completed and chromosomes are moved by MT to center of the cell. Differential growth of MT
MetaphaseChromosomes are aligned at the spindle equator on the metaphase plate.
AnaphaseBegins when sister chromatids split and move apart. APC is activated at beginning of anaphase and adds ubiquitin to proteins. Depolymerization of MT generates sufficient force to move the chromosome.
Spindle CheckpointOperates at the metaphase/anaphase transition to check for misaligned chromosomes. Unattached kinetochores contain a protein complex that send a wait signal.
TelophaseThe daughter cells return to interphase. Nuclear envelopes of the two nuclei are reassembled and chromosomes become dispersed.
CytokinesisIndentation of cell surface. Contractile ring theory.

Section 4

Question Answer
Signaling PathwaysConsist of a series of proteins. Each protein in a pathway alters the conformation of the next protein. Kinases add phosphate groups while phophatases remove them. Target proteins ultimately recieve a message to alter cell activity.
Protein Phosphorylation Can Change Protein Behavior in Different WaysIt can activate or inactivate an enzyme. It can increase or decrease protein-protein interactions. In can change the subcellular location of the protein. It can trigger protein degradation.
Extacellular Messengers Small molecules such as amino acids and their derivatives. NO and CO. Steroids. Eicosanoids.
Receptor Types GPCR, RTK, ligand gate channels, steroid hormone receptors
Signal Transduction by G proteinLigand binds to the receptor, the receptor's affinity for the G protein increases. The GDP on G protein is exchanged for GTP and thus promoting association with the effector.
Termination of G proteinDesensitization: blocking active receptors from turning on additional G proteins. GRK: inactivates a GPCR via phosphorylation. Termination of the response is accelerated by regulators.
Second MessengerSubstance released into interior of cell as a result of binding of the fist messenger to receptor on outer surface of cell.
PI- Derived Second MessengersPhosphates are added to PI to make PIP2. PLC breaks down PIP2 IP3 and DAG. DAG activates PKC. IP3 releases CA2+
Response to glucagon or epinephrineThese hormones stimulate glycogen breakdown (Phosphorylase), inhibit its synthesis (Synthase) and induce genes of glucose synthesis.

Section 5

Question Answer
Receptor Protein Tyrosine KinaseLigand binds and causes the monmers to dimerize, they then are able to autophosphorylate. It creates SH2 or PTB domains that attract signal molecules with the same domains.
The Ras-Map Kinase PathwayThe Ras is a G protein embedded in the membrane by a lipid anchor. Active when bound to GTP. Ras-GTP binds and activates downstream signaling proteins
G-Protein Accessory ProteinsGAPS: shorten the active time of Ras. GEFs: stimulate the exchange of GDP for GTP, activating. GDIs: inhibit the release of GDP, keep protein in inactive form.
Steps of MAP Kinase CascadeGrowth factor binds, autophosphorylate of receptor. Recruitment of Grb2-Sos and activation of Ras. Recruitment and activation of RAF. Phosphorylation scheme results in an activated transcription factor. MAPK translocates into nucleus and activates TF.
Scaffolding ProteinsFunction to tether members of a signaling pathway in a specific spatial orientation to enhance their mutual interactions. Some can induce a conformational change.
Signaling pathways can converge, diverge or crosstalkSignals from unrelated receptors can converge to activate a common effector. Identical signals can diverge to activate a variety of effectors. Signals can be passed back and forth between pathways as a result of crosstalk.