Chapter 8 (The developing cell) Flashcards
What are chromosomes?
Linear structures
Consist of one molecule of DNA
Found in pairs
During interphase, length of DNA are wrapped around specialised proteins called histones to form chromatin
What are chromatids?
Part of a chromosome after it has undergone SCR.
Each sister chromatid is genetically identical to its sister
What are homologous chromosomes?
Have same:
- Biochemical structure
- Physical shape and size
- Sequence of genes
- Gene loci (position of genes)
- Centromere position
Have different:
- Origins (one maternal and one paternal)
- Alleles
What is the cell cycle?
Cycle of cell growth, maturity and division.
Highly ordered sequence of events
Process that all somatic cells in multicellular organisms use to grow and divide.
produces two genetically identical daughter cells.
Length of cell cycle?
Varies between different cell types.
Eg, bacteria - 20 mins
Yeast: 1-3 hours
Hepatocyte: Up to year.
Cell theory?
All living things are made of one or more cells
The cell is the smallest unit of life
All new cells from preexisting cells
All existing cells have a common chemical composition: Carbohydrates, proteins, lipids, nucleic acids
Hereditary information is passed from one generation to the next as genes/DNA is passed from parent cell to daughter cell.
Key events of cell cycle?
Interphase: 90% G1 S G2 M C
Mitosis 10%
Cytokinesis
Importance of mitosis?
- Growth of multicellular organisms - increase no. cells and increase size and mass of tissues.
- Repair of damaged tissues
- Replacement of cells
- Asexual reproduction.
What happens at G1?
Growth 1
- Cells increase in size and mass
- All metabolic processes remain active, eg, protein synthesis, hormone production and respiration.
- Organelles replicated (except chloroplasts and mitochondria)
- Increased protein synthesis occurs
What happens at G1 Checkpoint?
Cells check:
- Chemicals needed for replication are present
- For damage in DNA before entering S-phase.
- Cell has suitable size
- Cell has sufficient nutrients
If conditions are not correct, the cell enters a resting state (G0) and no longer divides
What happens at S phase?
Synthesis
- DNA is replicated using semi-conservative replication
What happens in G2?
Growth 2
Chloroplasts and mitochondria increase in size and divide (increase in number)
Cell continues to increase in size and mass
Energy stores are increased
Spindle fibres start to form
What happens at G2 checkpoint?
Cells check:
All DNA has been replicated without damage
Cell is off correct size
If this is correct, cell passes into mitotic stage
Info on mitosis in cell cycle?
Nuclear division
Sub divided:
PMAT
Cytokinesis information?
Equal division of cytosol and organelles to form 2 genetically identical daughter cells.
Process is different in both animal and plant cells.
Cells that lose the ability to divide information?
Neurones, erythrocytes, muscle cells
These cells leave the cycle either temporarily or permanently due to:
- Differentiation (cells become specialised and can no longer divide)
- Damaged DNA - cell is no longer viable so enters G0.
Most cells can only divided a finite number of cells.
Cell cycle control information?
Sequence and timing of cell cycle controlled by cyclins (specialised proteins)
Cyclins activate enzymes called cyclin-dependent kinases CDKs.
Kinases catalyse the addition of a phosphate group onto a protein (Phosphorylation)
Phosphorylation of a protein changes its tertiary structure of cyclins
Specific CDKs control specific steps in the cell cycle and cell cycle is stopped if errors are detected.
Example of cell cycle control?
If DNA is damaged, then p21 (protein) binds to CDK.
This halts cell cycle at G1 stage in interphase.
Mutations to CDK genes can lead to failure to repair DNA -> cancer
Principle of mitosis?
Nuclear division to produce 2 genetically identical nuclei
Which are then distributes into two genetically identical daughter cells when the cell cycle is complete and cytokinesis occurs.
Interphase information?
Cell is still very active:
- Respiration
- DNA replication
- Protein synthesis
- Organelle replication
- Active transport/bulk transport
Cells grow and synthesise additional proteins, organelles and DNA ready for nuclear and cell division
What happens in prophase?
- Longest phase of mitosis
- Chromosomes shorten and thicken
- Each chromosome consists of 2 sister chromatids joined by centromere
- Centrioles move towards poles
- Microtubules form
- Nucleolus and nuclear envelope breaks down.
What happens in metaphase?
- Chromosomes line up on equator
- Spindle fibres attach to centromere (made from microtubules)
What happens in anaphase?
- Rapid phase
- Spindle fibres contract
- Exerts pulling force on centromeres
- Centromer splits
- Daughter chromosomes pulled to opposite poles, centromere first
What happens in telophase?
- Daughter chromosomes reach poles
- Chromosomes uncoil and lengthen
- Spindle fibres disintegrate
- Nuclear envelope reforms around chromosomes at each pole
- Nucleolus reforms
