Sec 5- Mitosis and Cell Division Flashcards
Unit II- Life of a Cell
What is a chromosome?
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).
What is chromosome number?
A eukaryotic cell’s DNA is divided into a characteristic number of chromosomes.
- Sum of all chromosomes in a cell of a given species.
What are sister chromatids?
One of two attached members of a duplicated eukaryotic chromsome.
What is a centromere?
Contricted region in a eukaryotic chromosome where sister chromatids are attached.
What are nucleosomes?
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.
What does “Chromo” refer to?
‘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).
What does multiplication by division mean in mitosis?
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).
When a cell divides using mitosis…
…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.
Why do cells divide (using mitosis)?
- Multi-Cellular Organisms
- -Growth
- -Repair
- Single-Celled Organisms (Eukaryotes)
- -Reproduction of organism
What is the life of a cell?
The life of a cell (cell cycle) starts when a new cell forms, and ends when the cell reproduces.
- It includes two main phases:
- Interphase
- Mitotic phase (M phase)
What is interphase?
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)
Why do some cells permanently enter G0?
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
What does M phase consist of?
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.
What are the four parts of Mitosis?
- Prophase
- Metaphase
- Anaphase
- Telophase
Pay Me Any Time!
What is the purpose of Mitosis?
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).
What happens at the end of G2 (Interphase)?
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.
What happens in the synthesis phase?
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.
What happens in prophase?
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
What are mitotic spindle?
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.
What is metaphase?
Chromosomes line up in the middle of the cell.
What is the anaphase?
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!
What is the telophase?
Events in telophase are the reverse of prophase events!
- Chromosomes decondense
- Spindle disassembles
- Nuclear envelopes forms
What is cytokinesis?
- Typically occurs during telophase
- Cytoplasmic division is called cytokinesis
- A cleavage furrow forms during cytokinesis in animal cells
How/Why does bacteria divide by binary fission?
- 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.
Why does cell division need to be controlled?
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
Cell Cycle Checkpoints:
- G1 Checkpoint
- Is the DNA okay? - G2 Checkpoint
- Did the chromosomes duplicate correctly - M Checkpoint
- Did spindle fibers attach to the kinetochores correctly?
Why do cyclins regulate the cell cycle?
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
What are kinases?
Kinases are proteins that add a phosphate group to other proteins (phosphorylation).
- Added phosphate groups sometimes activate and sometimes inactivate proteins.
- Cell cycle prgression:
- Cyclins bind cyclin-dependent kinases (Cdks)
- Cdks become phosphorylated themselves
- Cdks then phosphorylated target proteins that are needed for the next step of the cell cycle
What are the negative regulators of the cell cycle?
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.
What is cancer?
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.
How is a (benign) tumor different from cancer?
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).
What are the types of cancer?
Cancer are divided into three groups:
1. Carcinomas (90%)
* Arise from epithelial cells
* Skin, breast, colon, lung, liver, bladder
- Sarcomas
* Bone, muscle - Leukemias/Lymphomas
* Blood Cancers
Why can malignant tumors be fatal?
- Bodily resources are squandered
- Cells do not perform their normal function
- Tumors can block and destroy organs
What are the treatments of cancer?
- 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
What causes uncontrolled cell division?
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
- Tumor suppressor genes
* Stop cell cycle progression
* They can cause cancer when they are not functioning (negative regulators)
* Examples are p53 and Rb
