M2C6 - Cell cycles Flashcards
What is interphase?
long periods of growth and normal working
What happens during G1?
G1 is the first growth phase. During this phase the cell grows in size, protein synthesis occurs and organelles duplicate. Largest number of cells.
What happens during S?
S is the synthesis phase. During this phase DNA is replicated. Each chromosome is duplicated.
What happens during G2?
G2 is the second growth phase. During this phase the cell grows in size, energy stores increase and the replicated DNA is checked.
What happens during G0?
This is the phase when a cell has left the cell cycle. It can occur because:
-An issue has occurred during a phase of the cell cycle e.g. DNA is damaged.
-If the cell has differentiated to perform a specialised function (it will now no longer divide).
-Can also occur due to the age of a cell - cells will only replicate a limited number of times before entering G0.
What is the role of checkpoints?
Control mechanisms that monitor and verify whether the processes at each phase of the cell cycle have been accurately completed before the cell is allowed to progress into the next phase.
What happens at G1 Checkpoint?
Checks for DNA damage (that DNA has been replicated correctly), cell size, nutrients, growth factors.
What happens at G2 Checkpoint?
Checks for cell size, DNA replication.
What happens during Prophase?
- Chromosomes condense
- Chromosomes have become visible (but are
unordered)
-Nuclear envelope and nucleolus break down and have disappeared.
-Centriole divides in 2 and each daughter centriole moves to opposite ends of the cell.
-Each centriole begins to make a spindle.
What happens during Metaphase?
Chromosomes move to the middle of the cell (the equator) and become attached to the spindle at the centromere (crossover point of chromosome).
What happens during Anaphase?
- Spindle fibres are shortening
- Centromere splits and chromatids are separating and are being
pulled to opposite sides of the cell.
What happens during Telophase?
Chromatids have been pulled to opposite sides
of the cell
* A new cell membrane is visible down the
centre of the cell
-nuclear envelope reforms around each individual set of chromatids.
-Chromosomes uncoil
-Cytokinesis / the cell is beginning to divide
What happens during Cytokinesis in animals?
-A cleavage furrow forms in the middle of the cell
-The plasma membrane is pulled inwards by the cytoskeleton until it fuses in the middle forming 2 separate cells.
What happens during Cytokinesis in plants?
-The cell walls prevent a cleavage furrow from forming.
-Vesicles from the Golgi apparatus assemble where the metaphase plate was and fuse together, dividing the cell down the middle.
-Cell walls form along these sections of membrane forming
a cell plate.
What happens during Prophase 1?
Chromosomes condense, nuclear envelope disintegrates, spindle forms.
-Unlike mitosis, the homologous chromosomes pair up to form bivalents. The homologous pairs then cross over.
What happens during Metaphase 1?
Homologous pairs line up at the centre rather than individual chromosomes.
-Because the pairs randomly line up, each chromosome in the pair can end up facing either pole. This is called independent assortment. And allows for genetic variation.
What happens during Anaphase 1?
-Homologous pairs are pulled to opposite poles but chromatids stay attached.
-The sections of sister chromatids that had crossed over during prophase 1 now break off and swap places.
-This is called genetic recombination.
>Formation of chiasmata (links non sister chromosomes in genetic recombination).
>Exchange of genetic material
-This swapping can lead to a new combination of alleles which was not present in either of the original chromatids
-This mixing up of alleles leads to further variation.
What happens during Telophase 1?
-Similar to telophase in mitosis:
-Chromosomes assemble at each pole, the nuclear envelope reforms and the chromosomes uncoil.
-Cytokineses then occurs forming 2 daughter cells. These cells are haploid.
What happens during Prophase 2?
Chromosomes condense, nuclear envelope disintegrates, spindle forms.
What happens during Metaphase 2?
The individual chromosomes line up at the centre, like in mitosis.
There is more independent assortment so further genetic variation here.
What happens during Anaphase 2?
Chromatids rather than chromosomes are pulled to opposite poles (like in mitosis)
What happens during Telophase 2?
Chromatids assemble at each pole, the nuclear envelope reforms and the chromosomes uncoil. Like mitosis.
Cytokineses then occurs forming 2 daughter cells, each with half the number of chromosomes (haploid).
What are homologous chromosomes?
Two chromosomes in a pair – normally one inherited from the mother and one from the father. Carry the same genes at same loci.
How are erythrocytes specialised for their function?
Flattened biconcave shape, which increases SA:V, essential role is to transport oxygen round the body. I
-Don’t have nuclei or many other organelles which increases space available for haemoglobin.
-Also flexible to squeeze through capillaries.
How are Neutrophils specialised for their function?
Have a multi-lobed nucleus, makes it easier for them to squeeze through small gaps to get to site of infection. Granular cytoplasm contains many lysosomes that contain enzymes used to attack pathogens.
How are Sperm cells specialised for their function?
Have a tail/flagellum, so they are capable of movement.
Contain many mitochondria to supply energy needed to swim.
A chromosome on the head contains digestive enzymes, which are released to digest protective layers around the ovum.
How are Palisade cells specialised for their function?
Rectangular which can be closely packed to form a continuous layer.
Thin cell walls, increasing rate of diffusion of Co2.
Chloroplasts can move within cytoplasm to absorb more light.
How are Root hair cells specialised for their function?
Present at surface of roots near growing tips, have long extensions (root hairs), increase SA which maximises uptake of water and minerals from soil.
How are Guard cells specialised for their function?
When guard cells lose water and become less swollen as a result of osmotic forces, they change shape, and the stoma closes to prevent further water loss. Cell wall of cell is thicker on one side so cell doesn’t change symmetrically as volume changes.
How is Squamous epithelium specialised for its function?
Made of specialised squamous epithelial cells. Very thin due to flat cells that make it up and also the fact that it is one cell thick.
It is present when rapid diffusion across a surface is essential. E.g. forms lining of lungs and allows rapid diffusion of oxygen into blood.
How is Ciliated epithelium specialised for its function?
Made of ciliated epithelial cells. Have cilia on surface that move.
Lines the trachea e.g. causing mucus to be swept away from the lungs. Goblet cells are also present, releasing mucus to trap unwanted particles preventing particles from reaching alveoli.
How is Cartilage specialised for its function?
Connective tissue found in outer ear, nose and at ends of bones.
Contains fibres of elastin and collagen. Firm, flexible tissue composed of chondrite cells embedded in an extracellular matrix. Cartilage prevents bones from rubbing together and causing damage.
How is Muscle specialised for its function?
A tissue that needs to be able to shorten in length in order to move bones, which in turn move the body. There are different types of muscle fibres. Skeletal muscle fibres contain myofibrils which contain contractile proteins.
How is Xylem tissue specialised for its function?
The tissue is composed of vessel elements, which are elongated, dead cells. Strengthened by waterproof material lignin which provides support.
How is Phloem tissue specialised for its function?
Composed of sieve tube cells separated by perforated walls (sieve plates).
Why is mitosis significant in life cycles?
For growth, replacement and repair of tissues. Also necessary for asexual reproduction.
Describe the process of budding:
-This occurs in unicellular living organisms (such as yeast fungus) and multi-cellular organisms (such as Hydra and Sponges).
-In yeast, the bud emerges as a lateral bulge in the cell, then the cell nucleus is divided into two. One of them remains in the parental cell and the other immigrates to the bud.
-A bud grows gradually and remains connected to the parental cell until is fully grown then separates from it or remains to form a colony.
How are erythrocytes and neutrophils made and how do they differentiate?
-Produced from stem cells in bone marrow
Erythrocytes = As they differentiate they lose their nucleus and organelles to make room for haemoglobin, lots of haemoglobin is synthesised, and they develop a biconcave shape to increase SA:V.
Neutrophils = As they differentiate many lysosomes are produced
What are stem cells?
Unspecialised cells capable of developing into many different types of cells.
What are Totipotent stem cells?
Can differentiate into any cells e.g. Zygote and EARLY embryo.
What are Pluripotent stem cells?
Can form all tissue types but not whole organisms.
What are Multipotent stem cells?
Can only form a range of cells within a certain type of tissue.
What are the 2 sources for animal stem cells?
-Embryonic stem cells: Totipotent until birth.
-Adult stem cells: Bone marrow or umbilical cord. Multipotent cells.
What is the source for plant stem cells?
Meristem - pluripotent
What happens when xylem vessels differentiate?
-Elongate
-Become reinforced with lignin
-Ends of the cells break down to form a continuous hollow tube.
What happens when sieve tubes (phloem) vessels differentiate?
-Elongate
-Aren’t reinforced with lignin.
-Lose cell content - no nucleus and very little cytoplasm.
-Their ends don’t break down completely, but form sieve plates between the cells.
How can embryonic stem cells be used in medicine?
-New brain cells
-Rebuilding bones and cartilage
-Repairing spinal tissue
-Replacement heart valves.
How can cells from embryos have a practical use for biological knowldege?
-Grown into different tissues to test effectiveness of drugs.
-Can be grown into tissues to test for side effects of drugs.
-Cell function can be studied to find out what affects it in certain diseases.
What are some ethical issues with using embryonic stem cells?
-Removal of stem cells destroys the embryo.
-Originally the embryos used were left over from IVF, but laws have changed so now embryos can be created for the purpose of stem cell research.
