Cell Bio Exam 4

What is a chromosome?

Strings of DNA wrapped around proteins to make them compact. Ways for cells to organize and store DNA.

What is a chromatid?

One half of a duplicated chromosome.

What is a centromere?

A constricted region of the chromosome where the kinetochores form and the spindle microtubules attach. Also where the chromosomes are joined together, “the waist”

Different centromere attachments:

What are telomeres?

Protective caps or repeated regions on the ends of chromosomes. Every time a cell replicates a little bit gets sliced off.

What are sister chromosomes?

Two identical copies of a single replicated chromosome

What is a homologous pair?

Two sets of chromosomes (2n) one coming from each parent. They are similar in structure, size and carry similar genetic information.

Discuss topological equivalence in regards to the nucleus

The cytoplasm and nucleus are ________ ________ because the outer and inner nuclear membranes are continuous with one another, so that the flow of material between the nucleus and cytosol occurs without crossing a lipid bilayer.

What is RAN?

Nuclear import is powered by ____, a monomeric G-protein. The conformation of ___ will be different within the nucleus and within the cytoplasm. It is a monomeric G-protein that functions as a nuclear shuttling protein.

What is RAN-GAP?

Present only in the cytoplasm. This means that ___ can hydrolyze GTP only while it is in the cytoplasm.

What is RAN-GEF?

Present only in the nucleus (it binds chromatin). This means that ___ can bind GTP only while it is in the nucleus.

What is regulating what enters or exits the nuclear pore?

Comes mainly from the disordered FG-nucleoporins in the central channel. The FG-repeat mesh in the central channel is the selectivity barrier. It blocks free diffusion of large molecules. Cytosolic fibrils with FG repeats. The cytoplasmic filaments carry FG-nups that capture incoming receptor-cargo complexes and position them at the channel entrance. The basket on the nuclear side also carries FG-nups. It helps receptor-cargo complexes dock and be released on the nuclear side, and it handles mRNA export surveillance before mRNP’s leave.

What is nuclear export?

Moves cargo from the nucleus to the cytoplasm through the pore, using same machinery as import but run in reverse.

What are the steps for protein export?

1. Cargo is tagged. Proteins to be exported carry a nuclear export signal

2. Complex forms in the nucleus. The exportin CRM1 binds the NES-cargo only when it’s bound to RanGTP.

3. Transit through the pore. CRM1 interacts with the FG repeats in the central channel and carries the cargo across.

4. Disassembly in the cytoplasm. RanGAP stimulates Ran to hydrolyze GTP to GDP, which makes CRM1 release the cargo.

5. Recycling, CRM1 returns to the nucleus, and RanGDP is brought back by NTF2, where RCC1 (RanGEF) reloads it with GTP.

What part of the cell cycle takes the longest amount of time to complete?

Interphase

What is the centrosome?

A major microtubule-organizing center (MTOC) in animal cells. A non-membrane bound organelle, made of dense mass of protein and always contains 2 centrioles inside. Tubulin polymerizes from y-TuRCs.

How is the cell cycle regulated?

Based on a group of cyclically-activated protein kinases called Cyclin-dependent kinases (Cdks). In order to function as kinases, Cdks must be bound to their regulatory protein cyclin.

What is the longest phase of meiosis?

Prophase I

What are the phases of Prophase I?

1. Leptotene: nuclear membrane, condensation of chromosomes

2. Zygotene: formation of bivalent, formation of synaptonemal complex, synapsis between homologous chromosomes

3. Pachytene: crossing over

4. Diplotene: chiasma, dissolution of synaptonemal complex

5. Diakinesis: dissolution of nuclear membrane

How do chromosomes move to opposite poles during anaphase?

Dynamic instability (depolymerization): kinetochore microtubules shorten, mostly by losing tubulin subunit at the plus end (at the kinetochore). The kinetochore stay attached to the shrinking end and is pulled along, a ‘pac-man’ mechanism.

Motor proteins: kinetochore-associated motors and microtubules-depolymerizing kinesins help drive disassembly and keep kinetochores coupled to the shortening fibers.

What is separase?

Breaks down cohesion and allows separation of chromatids

What is shugoshin?

Protects cohesins

What are cytosolic fibrils?

Contain phenylalanine and glycine repeats. (known as FG repeats) and they are thought to be the binding sites for nuclear import receptors.

What is a nuclear basket?

A filamentous, cage-like protein structure attached to the nucleoplasmic side (the inside facing the nucleus) of the nuclear pore complex in eukaryotic cells

What are channel nucleoporins?

The proteins that compose nuclear pore complexes. Present in multiple copies within a single nuclear pore