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61 Cards in this Set

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  • Back
In slides of cells, when looking at the nucleus, to what do the lighter and darker staining regions usually correspond?
lighter - euchromatin (trxn accessible)
darker - heterochromatin (condensed, trxn inactive state)
What does the relative abundance of the dark and light regions in a cell nucleus indicate?
Indicates the activity of the nucleus, and thus the cell. Lighter nuclei, or the presence of lots of EUCHROMATIN indicates a very ACTIVE cell that is transcribing lots of DNA and probably making lots of protein.
What delineates the nucleus?
What is special about the outer memberane?
An inner and outer nuclear membrane, seperated by the perinuclear cisterna. The outer membrane is continuous with the ER and may be studed with ribosomes. The perinuclear cisternal space can be continuous with the ER.
Whare are nuclear pores?
Openings in the nuclear envelope which mediate the transport of material into and out of the nucleus.
What is the Nucleolus (nucleoli)?

What can nucleoli indicate about a cell?
-Region of nucleus
-Congregation of chromosomes carrying genes for ribosomal RNA (rDNA)
-Synthesis of rRNAs. (rDNA

-Combination of rRNAs with proteins to form ribosomal subunits to be exported. (rRNA + Proteins -> ribosomal subunits) --- go out into cytoplasm to make new protein

Presence of large or multiple nucleoli indicative of active cell
Differentiate between Faculatative and constitutive heterochromatin.
Facultative- DNA shut down until its needed, chromatin can be unwound to become euchromatin
Constitutive - rarily if ever transcribed, always condensed, usually found at the outer edge of nucleus just under the nuclear membrane.
What are some of the levels of DNA packing into chromosomes?
The DNA double helix is wound around histone proteins, forming histones (beads) which are connected by linker DNA. Solenoids, which are 30nm (across) lengths of chromatin are formed from nucleosomes, creating fibers that are condensed/twisted up to make loops and eventually into chromosomes.
What are histones?
Family of highly basic (+)proteins (h2a, h2b, h3, h4) which form an octameric core and are used to pack DNA into nucleosome units (11nm). An additional histone protein, H1, and some non-histone proteins help condense DNA into solenoid 30nm fibers.
What is the role of the nucleoskeleton?
Organizes the chromatin wtihin the nucleus, in part by interaction with the nuclear lamina. The scaffold for chromosomes in the nucleus is formed by acidic proteins (-).
What is the role of the nuclear fibrous lamina?
It supports the nuclear envelope, and is made of many proteins like nuclear lamins (A,B,C), which are made of intermediate filaments. These proteins help chromatin attach to the nuclear envelope, give structure to the envelope, and help reassemble the envelope after mitosis.
What are the types of intermediate filaments and where are they found?
Nuclear Lamins: Cell Nucleus
Keratins: Epithelial Cells
Vimentins: Connective Tissue
Desmin: Muscle
Glial Fibrillary Acidic Protein: Glial Cells
Neurofilaments: Neurons
What is a NLS and why is it important?
Nuclear localization signal, proteins need it to be imported into the nucleus through nuclear pores. Importins interact with fibrils and NLS.
What are importins?
Nuclear import receptors. Help proteins to access the nucleus via fibrils.
What triggers the nuclear envelope break down in mitosis (in part) >
Phosphorylation of nuclear lamins which make up the nuclear fribrous lamina.
Describe nuclear pores and what is the role of nucleoporins in the pores?
Complex, made of 100+ proteins, including nucleoporings, which establish a channel for transport.
How does transport in/out of nuclear pores proceed?
Small molecules (<40kDaltons) can diffuse freely, larger materials like proteins, ribosomal subunits, etc. must be actively transported. Transport is specific and is controlled by nuclear import and export signals and chaperone proteins.
Describe the nucleolus substructure and the functions of each area
Fibrillar center - rDNA not being transcribed
Dense Fibrillar Zone - rDNA transcribed to rRNA
Granular Zone - ribosomal packing and processing
Where can the nucleolus be found in the nucleus?
Nucleolus condense around the nuclear organzing regions of 10 interphase chromosomes which contrain the ribosomal DNA genes.
Define cancer.
. Cancer may be simply defined as cells that begin to divide continually, apparently without restraint, and with no regard to adjacent tissues or organs. These cells have thus escaped the carefully monitored controls of the cell cycle.
What are some basic functions of the cell cycle?
To copy and pass on the cell's genetic information to the next generation by forming two genetically identical daughter cells, whose DNA in each chromosome was accurately replicated and segregated. Also cells duplicate their organelles and macromolecules.
What are the phases in the cell cycle and how are they controlled in general?
4 unequal phases:
G1, S, G2, M
Controlled by extensive cell signaling.
What is a renewing population?
What is cytokinesis?
cells which divide, grow, differentiate and divide again.
When the cytoplasm and its contents separate in two.
What is interphase?
Interphase is the time during which the cell continues to transcribe genes, grow, differentiate, and carry out its assigned cellular functions. It is subdivided into a G1 (gap 1) phase, a S (synthesis) phase during which cells replicate their DNA in preparation for mitosis, and a G2 (gap 2) phase. Cells grow continuously during the three phases of interphase.
What are cells monitoring for during G1 and G2?
cell will monitor both internal and external conditions to make sure they are acceptable before committing to the M phase and cell division.
What are the phases of mitosis?
Prophase, metaphase, anaphase, and telophase.
What is G_0 phase?
Cells can opt out of the cell cycle during G1 and enter a quiescent G0 phase. Cells may remain in G0 until conditions for cell division improve or, in the case of nerve cells and skeletal muscle cells, the G0 phase is considered to be permanent.
What aspects of the environment are monitored at the G1 checkpoint ?
confirms that sufficient nutrients, are available for cell proliferation. Also, that the cell DNA is intact and “ready” for replication. Otherwise, the cell may enter G_0
What aspects of the environment are monitored at the G2 checkpoint ?
also monitors external conditions, perhaps making certain that the proper extracellular signals are present in order to proceed to mitosis successfully. Is the DNA replicated? A variety of internal signals must also be activated. For example, signals for inducing the formation of the mitotic spindle must be present.
What do kinases and phosphatases do?
Kinase: Phosphorylates a protein
Phosphatase: Dephosphorylates a protein
Phosphorylation and dephosphorylation are fast ways to turn a protein on and off.
What role does cyclin play in regulation of the cell cycle?
THE CONCENTRATION OF THE CYCLINS CONTROLS THE ACTIVATION OF the protein kinases M-Cdk (triggers mitosis) and S-Cdk (triggers DNA synthesis.
What kind of feedback mechanism is involved with anactivated M-cyclin-cdk compled?
There is a positive feedback mechanism in that each activated M-cyclin-Cdk complex will activate more of the same complexes in a geometric fashion. This rapid accumulation triggers the cell into the M-phase.
What are some of the basic characteristics of Cyclins and CDKs (cyclin dependent kinases)?
Cyclins are present in cell only at certain times and activate CDKs when around.

CDKs are always present in the cell, are normally inactive, phosphorylat other proteins when activated that drive cell cycle to the next phase.
What breaks down cyclin?
ubiquitin tags cyclin and proteosomes break it down
What is the cell checking for at the M checkpoint?
Are all chromosome aligned properly on metaphase plate?
What functions does MPF (cycling + cdk) have in mitosis?
Chromatin condensation due to phosphorylation of histone ! and condensins,
Phosphorylation of lamins causing nuclear envelope breakdown, fragmentation of golgi and ER, spindle formation
What kind of extracellular signal molecules are required for normal cell division and growth and where do they come from?
Most of the signal molecules are proteins either secreted by other cells, bound to surface of other cells, or in the extracellular matrix.

Mitogens - stimulate cell division
Growth Factors (GFs) -stimulate cell growth/increase in mass

Survival factors - promote cell survival by suppressin apoptosis.
What does p53 do for the cell?
p53 is a G1
checkpoint protein that monitors for DNA damage. If DNA is damaged, p53 stops the cell cycle so DNA can be repaired prior to replication.
What mitosis preparations occur in interphase?
The cell increases in size, DNA is replicated, centrosome is duplicated*.
*under a control checkpoint?
what occurs during prophase?
individualization of chromosomes, initiation of mitotic spindle, rupture of envelope

condensation of the chromatin (triggered in part by phosphorylation of the condensin family of proteins as well as H1) into mitotic chromosomes, and the initial growth of the microtubule-based mitotic spindle apparatus with its polar, astral, and kinetochore microtubules and their associated proteins including dynein and the kinesin microtubule motors.
what occurs during prometaphase?
breakdown of nuclear envelope, which then permits the attachment of spindle microtubules to the kinetochores of the chromosomes
What occurs in metaphase?
align the chromosomes at the Metaphase plate, spindle completed, disappearance of nuclear envelop and nucleolus
what occurs during anaphase early and late?
early: chromosomes pulled apart longitudinally, and migrate to poles
late: aggregation of chromosomes at the poles, beginning of cell division, initation of cleavage furrow
What occurs during telophase?
nuclear envelope reassembly, and decondensation of the chromatin, nucleolus reforms too, cytokinesis commences
Which end of the microtubule is anchored at the centrosome?
What is meant by the free ends being termed dynamically unstable?
The minus end.
They switch rapidly from uniform growth to rapid shrinkage.
How is the depolymerization of microtubles decreased when they interact with MTs from an opposite centromere?
When two microtubules from opposite centrosomes interact in an overlap zone, motor proteins and other microtubule-associated proteins cross-link the microtubules together (black dots) in a way that stabilizes their plus ends by decreasing the probability of their depolymerization.
what is a centriole made up of?
How are the δ-tubulin rings in the centrosome related to microtubules?
9 triplets of alpha and beta tubulin
They are the MT's nucleation sites
What do astral MTs do?

What are kinetochores?
Attach to plasma membrane

Where the spindle microtubules attach to chromosomes in the centromere (where the sister chromatids attach)
What is pulled apart during anaphase? What else is going on at this time?
Sister chromatids. The kinetochore microtubules shorten and the chromatid is pulled toward the poles(anaphase A). The polar microtubles are elongatin, thereby increase the separation between the spindle pores (anaphase B).
Describe how nuclear envelope breaks down and reforms during M phase
In prophase, the lamins (fibrous proteins inside nuclear envelope) are phosphorylated, which causes the envelope to break apart. In telophase the lamins are dephosphorylated and the lamins come back together and the nuclear envelope pieces fuse back together.
What is the major function of lamins?
To assemble and disassemble the nuclear envelope
What is the role of cohesin?
what is the role of condensin?
Keeps the sister chromatids together.
Helps with the coiling of DNA into chromosomes.
What does anaphase promoting complex do?
Triggers the separation of sister chromatids by promoting the destruction of cohesins.
What occurs during cytokinesis? When does this occur in the M phase?
What is the contractile ring made of?
Contractile Ring cleaves cytoplasm into two daughter cells
Begins in Anaphase and ends after Telophase
Signals end of M Phase
Actin and myosin
With respect to chromosomes, what is a:
and Translocation?
deletions: when a part of a chromosome is missing, or part of the DNA genome is missing
duplications: when a part of a chromosome is present in two copies,
inversions: when a chromosome breaks and a piece reverses and reattaches itself, nondisjunction: an error in cell division where the chromosomes fail to separate, so that both pass to the same daughter cell—this results in monsomy and trisomy)
translocation: when the location of specific chromosome material attaches to another chromosome
What is Down Syndrome the result of?
Trisomy 21: three copies of Chromosome 21.
How can chromosomal abnormalities be detected?
examine the karyotype: chromosomes are prepared, sorted, and examined according to their morphological features and staining patterns
What does the presence of a barr body in a cell indicate?
The sex of the individual, barr bodies are found in females (inactive X chromosomes).
What is amniocentesis?
Method to look at chromosomal abnormalities in a fetus using a sample of fetal cells from amniotic fluid.
What distinguished chromosomes?
Size and the placement of the centromere. Can have
metacentric, submetacentric, and acrocentric
What occurs during necrosis?
The cell membrane disintegrates, allowing lysosomal contents to enter the extracellular space and induce an inflammatory response.
What occurs during apoptosis?
The nucleus undergoes fragmentation with the loss of cell volume and cell membrane blebbing (looks like making small vesicles), not loss of cell contents, apoptoic bodies formed and a phagocytosed. no inflammatory response.