Chromosome Inheritance Session 18 Flashcards
What are chromatins?
- It is the the DNA and the protein collectively in the chromosome
How many chromosomes are there in the human body and what are the two different types ?
- There are 46 chromosomes /23 pairs
- 22 of them are called autosomes : which are found in both male and female
- 1 pair consists in sex chromosomes because they contain genes that control gender (X and Y)
What are the chromosomes male and females have ? ( X or Y)
- Males : XY
- Females :XX
What gene does the Y chromosome have and what does it help with ?
- It has the SRY gene that causes testes to develop
What are Karyotypes ?
- It is an artificial display of the chromosomes present in a cell during metaphase
What does the Centromere do ?
- It holds together the chromatids until a certain phase of mitosis , when the centromere splits
What are the two phases of the cell cycle ?
- Interphase and a Division Phase
What are the the 3 different phases during interphase and what happens in each of them ?
- G1 stage : the cell performs its normal functions and doubles its organelle and accumulates the materials needed for DNA synthesis
- S Stage: DNA replication happens and after this stage there are two identical sister chromatids
- G2 stage : synthesizes the proteins needed for cell division
If a cell never enters the S and G2 stages and are permanently arrested in G1 , what stage are they known to be in and name two types of cells that go through this process
- Nerve and muscle cells
- they are known to be in the G0 stage
What are the two stages that occur within Cell division (M phase) and what occurs within each of them ?
- Mitosis : a type of nuclear division , also known as duplication division since each new nucleus contains the same number and type of chromosomes as the former cell
- Cytokinesis : Division of cytoplasm
How is mitosis balanced out to keep it running continuously , what happens with the cells that are no longer needed after mitosis or have been excessively damaged ?
- Apoptosis occurs which is programmed cell death
How is the cell cycle controlled to ensure the conditions of each step is met ?
- By checkpoints at different stages of the cycle to ensure conditions are met
What are the 3 different checkpoints in the Cell Cycle ?
- G1, G2 and M checkpoint
What occurs during the G1 checkpoint ?
- Cells are checked here if they are capable of passing through and if they don’t pass through, they are sent to G0 , where they continue to perform normal functions but do not divide
- the integrity of DNA is also checked , if it is damaged , proteins such as p53 stop the cycle and place the cell in G0 , if they can be repaired , they can renter the cycle but if not they undergo apoptosis
What occurs in the G2 checkpoint ?
- The cell cycle is paused here to ensure that the DNA has replicated. If DNA is damaged , then it can be repaired here so it isn’t passed on to the daughter cells
What occurs at (M) Mitotic checkpoints and where does it occur ?
- It occurs between Metaphase and Anaphase
- it ensures that chromosomes are properly attached to the spindle so they can be distributed accurately to the daughter cells
What are some external controls of the cell division?
- hormone or growth factor can stimulate a cell to divide
What is the signal transduction pathway ?
- It is a pathway formed by proteins that pass the signal from one to the next
What do the genes , proto-oncogenes and tumour suppressor genes do ?
- Proto-oncogenes stimulate the cell cycle
- Tumor supressor genes inhibit the cell cycle
What are cyclins and what do they do ?
- They are a family of regulatory proteins that control the progression of the cell cycle
What are the different stages of mitosis ?
- Prophase
- Prometaphase
- Metaphase
- Anaphase
- Telophase
What is an Aster ?
- An array of microtubules
What does each centromere contain ?
- a pair of centrioles , which consist of short cylinders of microtubules (9 triplets).
What occurs during the prophase ?
- The centrosomes have duplicate (during early S phase ) , they move towards opposite ends of nucleus
- Spindle fibers appear
- Nuclear envelop begins to fragment
- the nucleolus disappears
- chromosomes condense and are now visible
What occurs during Prometaphase ?
- The spindle fibres attach to the centromeres as the chromosomes continue to shorten and thicken
- 46 chromosomes start moving toward middle of the cell
What occurs at metaphase ?
- Chromosomes attached to the spindle fibres line up at the metaphase plate
What occurs during Anaphase ?
- Centromeres divide , the sister chromatids separate and move toward opposite poles of the spindle
What occurs during telophase ?
- this only begins when chromosomes arrive at the poles
- chromosomes become indistinct chromatin again
- Spindle disappears
- nuclear envelope reappears
- nucleolus reappears
What occurs during cytokinesis ?
- division of the cytoplasm and organelle occur (not part of mitosis )
- an indentation called a cleavage furrow passes around the circumference of the cell.
How does the cleavage furrow occur ?
- Actin filaments form a contractile ring , then as the ring becomes smaller , the cleavage furrow pieces the cell in half
