Mitosis And Meosis Flashcards
How do eukaryotic cells, prokaryotic cells, and viruses undergo cell division?
Eukaryotic cells divide by mitosis or meiosis.
Prokaryotic cells divide by binary fission.
Viruses do not undergo cell division because they are non living. They replicate inside the invaded host cells.
What are the three stages of cell cycle?
Interphase ( G1, S, G2)
Nuclear division ( mitosis or meiosis )
Cytokinesis
What happens in the G1 phase?
Cells grow and increase in size in preparation for replication.
Proteins are produced in protein synthesis ( it is a slow process )
Increase in the number of organelles by duplication
Transcription of genes to make RNA
What happens in G2?
Same as G1
Spindle can begin to be formed
What are the stages of mitosis? Describe the features
Prophase, metaphase, anaphase, telophase
One round of nuclear division
Genetically identical cells wirh same genetic info as parents
Growth, repair of damaged tissues, asexual reproduction, production of new stem cells, development of body plan, producing gametes from haploid cells, proliferation of white blood cells
Diploid cells - 2 sets of chromosomes
Explain prophase
Chromosomes condense to become more visible ( by wrapping around histone proteins )
The nucleolus and nuclear envelope disappear/break down
Centrioles form, and move to opposite poles of cell. These produce spindle fibres. They create a spindle apparatus.
Explain what happens in metaphase
Chromosomes align along the equator of the cell
Chromosomes attach to the spindle fibres at the centromere
Explain anaphase
The spindle fibres contract, change length and pull the chromatids towards opposite poles. This causes the centromere to divide/break into two and chromatids pulled to opposite poles of the cell.
Why are two chromatids identical?
This is because the original DNA strand is replicated in semi conservative replication.
Explain telophase
The nuclear envelope and nucleus reforms and the chromosomes are at the opposite ends of the cell.
The spindle fibres disappear.
Chromosomes uncoil into chromatin ( DNA and histone proteins )
Cell surface membrane undergoes cytokinesis
How does cytokinesis occur?
Cytoplasm splits into two new daughter cells each with a nucleus.
Compare cell division in animals and plant cells
Animals involve centrioles, plants do not. For animals, the plasma membrane folds inwards and rips the cytoplasm. For plants, end plates form on the equator of the cell and cell division takes place through middle of cell. Vesicles from GA form structures down middle. Also, animal cells it can occur anywhere but cell division only occurs in meristem of plant cells.
How do chromosomes look in prophase?
They are scattered and dark bodies.
What types of cells are present in meristematic tissue, and how are xylem produced from them?
In the meristem, we find stem cells.
Differentiation occurs, cell elongation, lignin is deposited on cell walls ( of parenchyma cells to provide strength against negative pressure and waterproof the cell ). End walls break down to form a long hollow tube. Cell dies —-> limited lateral movement of water, allows adhesion
What are the specialisations of a sperm cell?
They have an acrosome containing enzymes to digest outer portion of egg and penetrate the egg
Mitochondria to allow the undilipodium to move.
Flagellum allows movement through the female reproductive system.
What are the specialisations of RBC?
Haemoglobin to combine with oxygen to form oxyhaemoglobin
No nucleus to contain more haemoglobin ( therefore no DNA )
Biconcave allows large SA:V so maximises oxygen absorption
Thin cells membranes for short diffusion path
Small/flexible to squeeze through capillaries
Carbonic anhydrase —> hc03- formation
How do stem cells become heamoglobin?
Synthesis haemoglobin
Remove nucleus, ribosomes, mitochondria
Become biconcave
Why do erythrocytes not make use of oxygen transported?
Oxygen is bound to the haemoglobin so no aerobic respiration can take place. Also, lack of mitochondria
What do the checkpoints do? What may happen if genetic info is not checked?
It checks DNA has been replicated correctly and that there is no errors.
This could lead to mutations and daughter cells will not receive identical genetic info.
Where does growth occur in plants? Where does cell division occur?
In meristem
In root tip
Why do we squash the cell?
To spread cells out so mitosis can be seen cleadly
What do neutrophils do and what are the specialisations?
They destroy pathogens by phagocytosis. They have a multi lobed nucleus to squeeze into the site of infection. They also have a flexible shape to squeeze through cell junctions.
Where do we find palisade cells? Specialisations?
Found towards upper surface of the leaf
Thin - short diffusion pathway for CO2 in
Lots of chloroplasts to maximise light absorption
Column shaped and arranged closely together
Where do we find ciliated epithelium cells? Function?
Trachea, bronchi
Goblet cells found between them
Cilia beat in rhythym to move mucus and trapped pathogens away from lungs
Where do we find squamous epithelial cells? Specialisations?
One cell thick and acts as a surface, fit together tightly for rapid diffusion pathway
Thin diffusion pathway —> short diffusion distance so efficient diffusion of gases
Held in place by a basement membrane ( made of collagen and glycoproteins )
Lining lungs, alveoli
What is a stem cell?
An undifferentiated cell that can differentiate into other cell types by expressing specific genes. They are capable of mitosis.
What is pluripotent?
The ability to become any cell type —> cannot give rise to extra-embryonic tissue
Normally embryonic stem cells
What is totipotent?
The ability to diffrentiate into any cell type in the body and form a whole organism
Zygote as can differentiate into any cell type and form a new organism ( or an early embryo )
What is a multipotent cell?
The ability to become a limited range of cells
Adult stem cells in the bone
What does meiosis do?
Produced genetically different daughter cells
Two haploid divisions to make 4 haploid cells ( genetically different gametes )
Explain the sources of genetic variation of meiosis
Independent assortment in metaphase 1 and 2
Homologous chromosomes randomly align on equator and maternal and paternal chromosomes face opposite poles
Crossing over of prophase 1
Crossing over of non sister chromatids resulting in an exchange of DNA and alleles between maternal and paternal chromosomes. Chiasmata forms at several points. Then, bivalents are formed with a new combination of alleles.
Mutation so change to the DNA base sequence
Random fusion of gametes
Non disjunction where homologous chromosomes have one more or one less chromosomes
Both move to one pole of the cell
What is non disjunction?
Homologous chromosomes do not separate and move to one pole of the cell
What are features of neutrophils?
Organelles like mitochondria , ribosomes, RER
Contains lysosomes which contain hydrolytic enzymes to break down engulfed particles
Can change shape
Flexible shape allows engulfin —> can squeeze into site of infection
Multi lobed nucleus
Engulf pathogens
What tissue undergoes mitosis?
Meristematic tissue
What is effect of mutation?
Different primary structure
Shorter due to deletion of stop codon
Function is lost
What happens if DNA does not replicate correctly?
Mutations
Protein does not function properly
Daughter cells do not receive identical genetic info
Why does meiosis need to have twice as many stages as mitosis?
To half the chromosome number
To separate chromosome pairs and sister chromatids
How to know if meiosis on a diagram?
Use the word mother cells for eg or 2n to n
Details about meiosis
Independent assortment of chromosomes of metaphase 1, chromatids in metaphase 2
Telophase 2 is formation of nuclear membranes q
Anaphase 1 = separation of sister chromosomes
Anaphase 2 = separation of sister chromatids
Why does the S phase occur?
DNA replication occurs so daughter cells have the same DNA and have a full copy of DNA
Why would a cell enter g0 phase?
The cell leaves cell cycle either temporarily or permanently after mitosis if cell has fully differentiated ( eg root hair cell, red blood cell ) or if the cell wants to repair damage to DNA
Not undergoing mitosis
What is the purpose of the G2 checkpoint?
Checks to see whether DNA has replicated correctly or not
Determines whether cell can undergo mitosis
How do stem cells become neutrophils?
Develop indentations in nucleus to become a lobed structure
Lysosomes accumulate
How is the phloem formed from stem cells?
Ends don’t break down —> form sieve tube elements and companion cells
Occurs from parenchyma cells
What are the potential uses of stem cells in research and medicine?
- treatment of neurological conditions ( Alzheimer’s, Parkinson’s )
Research into developmental biology
What is a homologous chromosome?
One
What is a homologous pair of chromosomes?
Pair of 2 X shapes
One is maternal, one is paternal
Same genes, different alleles, same length, centromere in same place
Why do gametes need to be haploid?
These is because when they fuse, they form a diploid zygote
What are the types of tissues?
- epethelial tissue —-> lines the organs and keeps them separate
- connective tissue ——> adds support and structure ( stuff like layers in skin and blood )
- muscle tissue ——> contracts
Why would a cell spend longer in the S phase?
More genetic material to synthesise
Why are onion cells used to view cells undergoing mitosis?
Site of cell division as contains meristem tissue
No chloroplasts present
Where are animal stem cells found?
Umbilical cord blood
Bone marrow
Embryonic tissue
What is the purpose of the G1 checkpoint?
Checks for DNA damage and ensures it does not enter S phase
What tissues are typically found in the lungs?
- squamous ( lining lungs, alveoli )
- ciliated ( trachea, bronchi )
- elastic tissue ( in blood tissues )
What tissues are typically found in leaves?
- palisade tissue
- epidermal tissue ( to prevent water loss )
- xylem
- phloem
Benefits of embryonic stem cell research on biological knowledge
- test how effective medicinal drugs are
- test for side effects
- studied to see how they develop into different cell types
Ethical issues with using embryos as a source of stem cells
- embryo has to be destroyed (i.e: via abortion), which is problematic
- debate about when life begins
- an embryo cannot give consent
Ethical issues with using bone marrow as a source of stem cells
- harvesting bone marrow is painful / risky
- babies may be conceived specifically to provide a bone marrow transplant for a sibling with a condition requiring the transplant
- babies cannot give consent for this
