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Bio181 > Sec 5- Mitosis and Cell Division > Flashcards

Sec 5- Mitosis and Cell Division Flashcards

Unit II- Life of a Cell

1
Q

What is a chromosome?

A

A eukaryotic chromosome is a molecule of linear DNA together with associated proteins.

  • Each species has a characteristic number of chromsomes (but all members of the species have the same number of chromsomes).
  • Each cell in a multi-cellular organism has the same number of chromsomes (with some exceptions!).
  • Genomic DNA is the sum of DNA of all chromosomes in a cell (= genome).
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2
Q

What is chromosome number?

A

A eukaryotic cell’s DNA is divided into a characteristic number of chromosomes.

  • Sum of all chromosomes in a cell of a given species.
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3
Q

What are sister chromatids?

A

One of two attached members of a duplicated eukaryotic chromsome.

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4
Q

What is a centromere?

A

Contricted region in a eukaryotic chromosome where sister chromatids are attached.

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5
Q

What are nucleosomes?

A

A lenght of DNA (146 nucleotide pairs) coiled around a core of eight histone proteins is called a nucleosome.

  • Histone proteins (+ charge) organize DNA (- charge) structurally.
  • The linker DNA between nucleosomes is about 60 nucleotide pairs long.
  • Nucleosomes are compacted into chromatin fibers, which supercoil into chromosomes.
  • Chromatin is the material, chromosome is the entire structure.
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6
Q

What does “Chromo” refer to?

A

‘Chromo” refers to color.

  • Chromosomes can be artificially colored with fluorescent labels.
  • They can then be artificially arranged by length (karyotype).
  • Each human chromosome has a number (higher number = decreased length).
  • One chromosome of each number is from the dad and one is from the mom.
  • The sex chromosomes are not numbered but are designated by a letter (X and Y).
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7
Q

What does multiplication by division mean in mitosis?

A

A cell reproduces by dividing in two.

  • Each descendant cell receives a full set of chromosomes and some cytoplasm.
  • Nuclear division mechanisms partition chromosomes of a parent cell into new nuclei (mitosis or karyokinesis).
  • The cytoplasm divides by a seperate mechanism (cytokinesis).
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8
Q

When a cell divides using mitosis…

A

…the two resulting cells are genetically identical to each other and the original cell.

  • They have identical chromosomes!
  • You start out with one parent cell and end up with two daughter cells.
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9
Q

Why do cells divide (using mitosis)?

A
  • Multi-Cellular Organisms
  • -Growth
  • -Repair
  • Single-Celled Organisms (Eukaryotes)
  • -Reproduction of organism
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10
Q

What is the life of a cell?

A

The life of a cell (cell cycle) starts when a new cell forms, and ends when the cell reproduces.

  • It includes two main phases:
    1. Interphase
    1. Mitotic phase (M phase)
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11
Q

What is interphase?

A

In interphase the cell is not dividing, but it may be getting ready for division.

It has three phases:
1. G1 (gap 1)
2. S (synthesis)
3. G2 (gap 2)

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12
Q

Why do some cells permanently enter G0?

A

When they no longer need to divide.

Ex of cells that don’t divide much are:
* Skeletal muscle
* Cardiac muscle
* Red blood cells (RBCs)
* Neurons

Ex of cells that divide often are:
* Skin cells
* Hair follicle cells
* Cells of stomach lining
* Nailbed cells
* Cells of the bone marrow that make RBCs and WBCs

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12
Q

What does M phase consist of?

A

M phase contains:
* Mitosis/nculear division (karyokinesis)
* Cell division (cytokinesis)

  • A typical dividing human cell takes ~24 hours to progress trough the cell cycle with ~1 hour spent in the M phase.
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13
Q

What are the four parts of Mitosis?

A
  1. Prophase
  2. Metaphase
  3. Anaphase
  4. Telophase

Pay Me Any Time!

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14
Q

What is the purpose of Mitosis?

A

Mitosis is a nuclear division process that maintains the chromosome number.

  • Each daughter cell has the same chromosomes as the other and as the parent cell.
  • Daughter cells are genetically identical (clones).
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15
Q

What happens at the end of G2 (Interphase)?

A

At the end of interphase the DNA is duplicated, but the chromosomes are not visible (blue area).

  • There are also two centrosomes (also replicated in the S phase).
  • Mitosis has not yet started.
15
Q

What happens in the synthesis phase?

A

In the synthesi phase of interphase the DNA of the chromosomes are duplicated (DNA replication), forming sister chromatids.

  • Sister chromatids are attached to each other at the centromere region.
  • Mitosis begins after G2.
16
Q

What happens in prophase?

A

Three things happen in prophase:
1. Chromosomes condense and become visible
2. The nuclear envelope disappears
3. The mitotic spindle forms and moves to opposite poles of the cell

17
Q

What are mitotic spindle?

A

Dynamically assembled and disassembled array of microtubles that moves chromosomes during nuclear division.

  • Microtubules of the mitotic spindle attach to the chromosomes at the centromeres, specifically to the protein region called kinetochore.
18
Q

What is metaphase?

A

Chromosomes line up in the middle of the cell.

19
Q

What is the anaphase?

A

Microtubles sperate the sister chromatids of each chromosomes and pull them toward opposite spindle poles.

  • Each DNA molecule is now a separate chromosomes.
  • zfor a short period there are now 92 chromosomes in a human cell!
20
Q

What is the telophase?

A

Events in telophase are the reverse of prophase events!

  1. Chromosomes decondense
  2. Spindle disassembles
  3. Nuclear envelopes forms
21
Q

What is cytokinesis?

A
  • Typically occurs during telophase
  • Cytoplasmic division is called cytokinesis
  • A cleavage furrow forms during cytokinesis in animal cells
22
Q

How/Why does bacteria divide by binary fission?

A
  • Bacteria are prokaryotic and don’t have a nucleus.
  • They don’t need to go through mitosis before cell divison.
  • Bacteria typically have one circular chromosome.
  • Multiple chromosomes don’t need to sorted and divided.
  • Bacteria divide by a process called binary fission.
23
Q

Why does cell division need to be controlled?

A

Different types of cells proceed through the cell cycle at different rates.

  • Locc of cell cycle controls may result in cells dividing at the wrong time and place.
  • Progression through the cell cycle can be aborted if the cell senses a problem.
    • too many cells already
    • faulty DNA replication
    • not enough resources available
24
Q

Cell Cycle Checkpoints:

A
  1. G1 Checkpoint
    - Is the DNA okay?
  2. G2 Checkpoint
    - Did the chromosomes duplicate correctly
  3. M Checkpoint
    - Did spindle fibers attach to the kinetochores correctly?
25
Q

Why do cyclins regulate the cell cycle?

A

They are needed at each checkpoint for progression and there is a sharp decline in their concentration after clearing the checkpoint.

  • Cyclins are proteins that are produced and degraded in the cell at various times in the cell cycle.
  • Cyclins control kinases
26
Q

What are kinases?

A

Kinases are proteins that add a phosphate group to other proteins (phosphorylation).

  • Added phosphate groups sometimes activate and sometimes inactivate proteins.
  • Cell cycle prgression:
    1. Cyclins bind cyclin-dependent kinases (Cdks)
    1. Cdks become phosphorylated themselves
    1. Cdks then phosphorylated target proteins that are needed for the next step of the cell cycle
27
Q

What are the negative regulators of the cell cycle?

A

The absence of some proteins is necessary for cell cycle progression.

  • p53 is an example
  • p53 is a negative regulator of the cell cycle that helps the cell clear the G1 checkpoint.
  • p53 assess if there is damaged DNA.
  • p53 recruits proteins to repair the DNA.
  • What happens if the DNA can’t be repaired? p53 does not function properly in many different cancers.
28
Q

What is cancer?

A

Uncontrolled cell division

  • Cancer is a malignant growth or tumor caused by abnormal and uncontrolled cell division.
  • Was named after the similarity in appearance of a malignant tumor to a crab.
29
Q

How is a (benign) tumor different from cancer?

A

Benign Tumor, Malignant Tumor, and Metastasis

Benign Tumor
* Abnormally growing and dividing mass of cells.

Malignant Tumor (Cancer)
* An abornal tissue mass that can spread into neighboring tissue and to other parts of the body.

Metastasis
* The spread of cancer cells beyond their original site (stage 4 cancer).

30
Q

What are the types of cancer?

A

Cancer are divided into three groups:
1. Carcinomas (90%)
* Arise from epithelial cells
* Skin, breast, colon, lung, liver, bladder

  1. Sarcomas
    * Bone, muscle
  2. Leukemias/Lymphomas
    * Blood Cancers
31
Q

Why can malignant tumors be fatal?

A
  • Bodily resources are squandered
  • Cells do not perform their normal function
  • Tumors can block and destroy organs
32
Q

What are the treatments of cancer?

A
  • Surgery to remove the tumor
  • Radiation therapy disrupts cell division (targeted)
  • Chemotherapy involves drugs that disrupt cell division
  • Non-cancer cells that normally divide rapidly also die: hair follicle cells, cells around fingernails, skin cells
33
Q

What causes uncontrolled cell division?

A

Caused by mutated genes that regulate the cell cycle.
1. Proto-oncogenes
* Promote cell cycle progression
* Are called oncogenes when mutated
* They can cause cancer when they are too active (positive regulators)
* Examples are Cdks and growth factors

  1. Tumor suppressor genes
    * Stop cell cycle progression
    * They can cause cancer when they are not functioning (negative regulators)
    * Examples are p53 and Rb

Bio181 (8 decks)

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