The Cell Cycle Flashcards
What is a genome?
Full genetic information of an organism, divided across chromosomes
Shape of eukaryotic chromosomes
Linear
Shape of prokaryotic chromosomes
Circular
What is chromatin?
- Makes up chromosomes
- DNA and associated proteins
What is the structure of a chromosome?
- Long, thin chromatin fibres, except for a period following DNA replication
What are sister chromatids?
- Two joined copies of a duplicated chromosome
- Initially attached by cohesin proteins
- Attached most closely at their centromeres
What are arms?
Portion of a chromatid to either side of the centromere
What is the cell cycle?
Ordered sequence of events from the origin of a cell to its division
What is interphase?
- Period of growth between cell divisions
- Subdivided into G1, S and G2 phases
What phase does DNA replication occur in?
Synthesis (S) phase
What is the mitotic (M) phase?
Where mitosis and cytokinesis occurs
What is mitosis?
- Cell division
- Produces two cells with identical genetic material
What are the 5 phases of mitosis?
- Prophase
- Prometaphase
- Metaphase
- Anaphase
- Telophase
What is mitotic spindle?
- Microtubules fibres and associated proteins
- In animal cells formation starts at centrosomes
What are asters?
Radial array of shorter microtubules extending from the centrosomes
What happens in the G2 phase?
- Two centrosomes have formed through duplication of a single centrosome
- Chromosomes are not condensed
What happens in prophase?
- Chromosomes condense
- Nucleolus disappears
- Mitotic spindle and asters begin to form
- Centrosomes begin movement towards opposite poles of the cell
What happens in prometaphase?
- Chromosomes condense further
- Nuclear envelope fragments
- A kinetochore forms on each centromere
- Kinetochore microtubules attach to each kinetochore
- Nonkinetochore microtubules interact with those from the opposite pole
What interacts with kinetochore microtubules?
Sister chromatid interact with kinetochore microtubules from opposite poles
What is a kinetochore?
A specialized protein structure
What happens in metaphase?
- Chromosomes are at the metaphase plate
- Centrosomes are at opposite poles of the cell and asters contact plasma membrane
What is a metaphase plate?
Imaginary plane midway between the spindle’s two poles
What happens in Anaphase?
- Cohesion proteins are split by separase, releasing sister chromatids
- Chromosomes move towards opposite ends of the cell
What are the two mechanisms to move chromosomes towards opposite ends of the cell?
- Motor proteins walk chromosomes along microtubules
- Motor proteins “reel in” the microtubules
Final result of anaphase?
- an elongated cell where each pole of the cell has a complete set of genetically identical chromosomes
What happens in telophase?
- Two nuclei form in the cell and nucleoli reappear
- Chromosomes become less condensed
- Spindle microtubules are depolymerized
- Cytoplasm is divided producing two daughter cells
What is depolymerization?
breaking a polymer down into monomers or other smaller units
What is cleavage?
- The process of cytokinesis in animal cells
- Involves pinching of plasma membrane
How is cytokinesis made possible?
By a ring of proteins (actin and myosin) that tightens to divide the cell into two.
What is myosin?
A motor protein
Cytokinesis in plant cells
- Cytokinesis occurs through the formation of a cell plate from vesicles containing cell wall materials
What undergoes binary fission and what does it mean generally?
- Prokaryotes divide by binary fission
- Process of dividing, resembles mitosis
What happens in binary fission?
- Cell enlargement, DNA replication and the dividing of the replicated chromosomes all occur at the same time
- Cytokinesis occurs through pinching of the plasma membrane
What is a check point?
A point where progression is stopped by a stop signal until a go-ahead signal allows it to continue
What are the 3 important checkpoints?
- G1 checkpoint
- G2 checkpoint
- M checkpoint
G1 Checkpoint
- Determines if cell division should occur
G2 Checkpoint
- Checks DNA integrity
- Ensures absence of mutations
- Makes sure all chromosomes are replicated
M checkpoint
- Checks that all sister chromatid are attached to kinetochore microtubules
G0 Phase
- A non-dividing phase of cells for cells that have left the cell cycle
- Can be reversible
What is cyclin?
- A protein whose concentration fluctuates throughout the cell cycle
- Concentration peaks during mitosis
What is cyclin-dependent protein kinases (Cdks)?
enzymes that only become active when they are bound to specific cyclin molecules, which help regulate the cell cycle
What is a maturation promoting factor (MPF)?
A cyclin-cdk complex involved in the G2 checkpoint
What are growth factors?
Proteins released by certain cells that stimulate others to divide
What does Anchorage dependence mean?
Division in most animal cells require that they be attached to a solid surface
What is density-depending inhibition?
When crowded cells stop dividing due to binding of cell-surface proteins of adjacent cells
How do cancer cells differ from normal cells?
- Continuously divide and don’t need normal signals regulating the cell cycle
- Replicate without growth factors
What does transformation mean?
Conversion of a normal animal cell into a cancerous one
What is a benign tumour?
- Cancer cells with too few mutations to spread to other parts of the body
What is a malignant tumour?
Cancer cells capable of spreading to new tissues
What is chemotherapy?
A drug that actively attacks rapidly dividing cells
What does taxol do?
- Type of chemotherapy drug
- Freezes the mitotic spindle by preventing microtubule depolymerization
What are HeLa cells?
Cancer cells taken from Henrietta Lacks without her consent
