Module 11 Flashcards

Question

Mitosis: Stage 1 - Prophase

Answer 1

Characterized by the appearance of visible chromosomes Outside of the nucleus the cell assembles a structure known as the → mitoic spindle Made of microtubules that pull the chromosomes apart into separate daughter cells The microtubule-organizing centers for animal cells → centrosomes Are duplicated and begin to migrate to opposite poles Plant cells also have microtubule-based mitotic spindles → but they lack centrosomes

Answer 2

The nuclear membrane breaks down and the microtubules of the mitotic spindle attach to the chromosomes The microtubules grow and shrink to explore the region that was once the nucleus As the ends of the microtubules encounter chromosomes → they attach to the centromeres of the chromosomes Each centromere is associated with 2 protein complexes called → kinetochores One kinetochore on each side of the centromere Each kinetochore is associated with one of the two sister chromatids Site of attachment for a single microtubule This arrangement is key for the separation of sister chromatids later in mitosis

Answer 3

One of the most visually distinctive stages of the cell during mitosis The spindle microtubules lengthen and shorten This pushes the chromosomes toward the center of the cell → aligns at the metaphase plate This is a single plane that is roughly equidistant from both spindle poles

Answer 4

The centromere divides and kinetochore microtubules shorten This pulls the chromatids apart toward the centrosome → ensures that one chromatid from each pair go to opposite poles

Answer 5

Complete set of chromosomes arrives at a spindle pole and cytosolic changes occur in preparation for the cell’s division The microtubules of the mitotic spindle break down and disappear The nuclear envelopes begin to re-form around each set of chromosomes → creates two nuclei Once the nuclear envelope is re-formed the chromosomes decondense and are less visible Telophase marks the end of mitosis

Answer 6

The next step in M phase is the division of the parent cell into 2 daughter cells → cytokinesis Cytokinesis begins with a ring of actin filaments that forms on the inner face of the cell membrane called the → contractile ring Forms at the equator of the cell perpendicular to the axis of what was the spindle The ring contracts → pinches the cytoplasm of the cell Divides it into 2 daughter cells

Answer 7

Mitosis is for the most part similar in animal and plant cells → but cytokinesis is different This is b/c plant cells have a cell wall and will need to construct a new cell wall for division to occur The plant cells form a structure called the phragmoplast in the middle of the cell during telophase The phragmoplast consists of overlapping microtubules These guide vesicles containing cell wall components to the middle of the cell Then during late anaphase and telophase the vesicles fuse to form a new cell wall in the middle of the dividing cell called the → cell plate The cell plate will fuse with the original cell wall at the perimeter of the cell This completes cytokinesis

Answer 8

Introduction It is important to control the cell cycle There are 2 events that are critical Initiation of DNA replication → G1 / S transition Initiation of mitosis → G2 / M transition Cells must have regulatory mechanisms to progress through the cycle Without these mechanisms the cell may undergo cell death or divide uncontrollably → cancer development

Answer 9

Through the cell cycle there is cyclic activity of protein and kinases → their combined activity controls cell cycle progression What are these proteins & kinases? Cyclins → regulatory protein subunits of specific protein kinases Their levels rise and fall with each turn of the cell cycle CDKs → kinases that phosphorylate other proteins whose actions are necessary for the cell cycle to progress Always present in the cell Active only when bound to appropriate cyclin

Answer 10

There are several different cyclins and CDK Act at specific steps of the cell cycle During G1 phase → the levels of cyclin D & E rise and activate CDKs It prepares the cell for S phase For example, it activates transcription factors that lead to the expression of DNA polymerase During S phase → cyclin-A levels increase, activating CDKs that initiate DNA synthesis During G2 phase → levels of cyclin B rise activating CDKs that initiate multiple events associated with mitosis Breakdown of nuclear envelope in prometaphase Formation of the mitotic spindle

Answer 11

At various stages of the cell cycle, checkpoints make sure the cell is ready to move on to the next phase There are 3 major stages in the cell cycle i. DNA damage checkpoint Checks for damaged DNA b4 it enters S phase ii. DNA replication checkpoint Checks for the presence of unreplicated DNA at the end of G2 b4 the cell enters mitosis iii. spindle assembly checkpoint Checks that all of the chromosomes are attached to the spindle before the cell progresses with mitosis

Answer 12

If DNA is damaged by radiation → activates a protein kinase that phosphorylates the p53 protein When p53 is phosphorylated, its level in the nucleus rises → this activates the transcription of several genes One of which is an inhibitor that blocks the activity of the G1/S cyclin-CDK complex → arrests the cell at the G1/S transition Gives the cell time to repair the DNA damage P53 is often called → guardian of the genome

Answer 13

What happens if the damage is not repaired in time? Once p53 is activated the DNA needs to be repaired quickly because phosphorylated p53 also.. Stimulates transcription of the Bax gene which codes for → Bax protein Represses transcription of the Bcl-2 gene which codes for → Bcl-2 protein In a healthy cell there is a balance of Bax & Bcl-2 → make Bax/Bcl-2 dimers This will shift the overall concentrations of Bax & Bcl-2 which results in the formation of → Bax / bax dimers

Answer 14

The increase of Bax/Bax dimers activates the pathway for programmed cell death → apoptosis This results in a controlled and orderly disintegration of the cell Apoptosis is important in the developing embryo → allows for remodeling of tissues E.g., developing hand looks like a paddle until cells are selectively killed In the adult → apoptosis has several important functions Maintenance of tissue size → eliminate excess cells to balance cell proliferation Elimination of specific cells → e.g., removal of activated T lymphocytes that are no longer required Elimination of genetically damaged cells → cells that are irreparable need to be removed The loss of the ability of cells to undergo apoptosis is a step to becoming cancerous

Answer 15

Group of diseases characterized by uncontrolled cell division There are cancer-causing genes known as → oncogenes First discovered in viruses Also altered version of proto-oncogenes → normal genes important in cell division Have the potential to become mutated into oncogenes There are tumour suppressor genes → inhibit cell division P53 protein is an example of a tumour suppressor The key is that cell division is regulated by Proto-oncogenes that promote cell division And tumour suppression genes that inhibit cell division This is a counterbalance system → must agree for cell division to take place Key features of cancer cells Ability to divide on their own without growth signals Resistance to inhibitory or cell death signals Ability to invade tissues → metastasis Promote new blood vessel formation → angiogenesis

Module 11 Flashcards

(39 cards)