Chapter Six: Cell Divisions Flashcards
How does cell division occur in eukaryotic and prokaryotic cells, and viruses?
- eukaryotic: enters the cell cycle and divides by mitosis or meiosis
- prokaryotic: cells replicate by binary fission
- viruses don’t undergo cell division since they’re non-living
What are the three key stages of the cell cycle?
- interphase (G1, S, G2)
- nuclear division (mitosis or meiosis)
- cytokinesis
What is interphase? what happens in each part of interphase?
- interphase is the longest stage in the cell cycle
G1:
- protein synthesis occurs to make proteins involved in synthesising organelles
- organelles replicate
- checkpoint at the end of G1, cell is checked that it’s the correct size and that there’s no damaged DNA
- if it doesn’t pass checks replication won’t continue and apoptosis may occur
S phase:
- DNA is replicated
G2:
- cell continues to grow, energy stores increase, and newly replicated DNA is checked for copying errors (DNA damage) at another checkpoint. if DNA is damaged the cell will try to repair the DNA
What does mitosis create, what is it used for, and what are the four key stages?
- creates two genetically identical diploid cells
- used for growth, tissue repair, and asexual reproduction in plants, animals, and fungi
the four key stages are:
1. prophase
2. metaphase
3. anaphase
4.telophase
What happens during prophase? what do plant cells have and don’t have in this stage?
- chromosomes condense and become visible. in animal cells, centrioles separate and move to opposite poles of cell
- centrioles create spindle fibres that are released from both poles, making a spindle apparatus that attach to the centromere and chromatids on the chromosome in late prophase, early metaphase
- plant cells have a spindle apparatus but don’t have centrioles
What happens during metaphase? what checkpoint occurs?
- chromosomes align along equator of cell
- spindle fibres released from centrioles and attaches to the centromere and chromatids
- spindle assembly occurs to ensure that every chromosome has attached to a spindle fibre before mitosis can proceed into anaphase
What happens during anaphase? what happens to the centromere? what does this stage require?
- spindle fibres start to shorten and move towards the centrioles to pull the centromere and chromatids they’re bound to towards the opposite poles
- this causes the centromere to divide into two and the individual chromatids are pulled to each opposite’s pole
- stage requires energy in the form of ATP which is provided by respiration in the mitochondria
What happens during telophase?
- chromosomes are at each pole and become longer and thinner again
- spindle fibres disintegrate, nuclear membrane reforms
What happens during cytokinesis? how are the cells split in animal cells and plant cells?
- the cytoplasm splits into two genetically identical cells
- in animal cells, a cleavage furrow forms in the middle of the cell and the cytoskeleton causes the cell surface membrane to draw inwards until the cell splits into two
- in plant cells, the cell surface membrane splits into two new cells due to the fusing of vesicles from the Golgi apparatus. the cell wall forms new sections around the membrane to complete the division into two cells
What is meiosis? what is a haploid and a diploid? how are genetic differences introduced in meiosis?
- meiosis: two nuclear divisions which result in four, genetically different haploid daughter cells
- the two rounds are referred to at meiosis I or meiosis II, both stages include all stages of cell division. interphase only happens at the beginning before meiosis I
- haploid (n): one copy of each chromosome
- diploid (2n): two copies of each chromosome
- the genetic differences are introduced by the two key processes in meiosis:
1. independent assortment of homologous chromosomes
2. crossing over
What difference happens in prophase 1? (crossing over)
- homologous chromosomes pair up, forming bivalents (two homologous chromosomes next to each other).
- crossing over genetic material can occur between the non-sister chromatids of bivalents
- breaks can occur in the genetic material where the chromatids cross over and parts of the chromatids are exchanged between the homologous pairs, resulting in new combinations of alleles in the resulting gamete
What difference happens in metaphase 1? what happens during metaphase 1? what is independent assortment and what does it result in?
- the homologous pairs of chromosomes assemble along the metaphase plate instead of individual chromosomes
- the homologous pairs of chromosomes line up opposite each other on either side of the equator, it is random on which side of the equator the paternal and maternal chromosome of each pair aligns (independent assortment)
- since there is 23 different homologous pairs, there are over 8 million different ways the pairs could assort themselves, meaning each gamete gets different combinations of the maternal and paternal chromosomes
- independent assortment results in genetic variation
what happens in metaphase II?
- the sister chromatids within one chromosome line up at the equator, their orientation on each side of the equator introduces another chance for increased genetic variation
how are multicellular organisms organised?
cells > tissue > organ > organ system > whole organism
what are the six specialised cells we need to know?
- erythrocytes
- neutrophils
- sperm cells
- palisade cells
- guard cells
- root hair cells
describe the structure and function of erythrocytes
- biconcave shape to increase surface area for diffusion and to increase cell flexibility so it can fit through narrow capillaries
- no nucleus for more space to hold haemoglobin to increase oxygen transport
describe the structure and function of neutrophils
- lobed nucleus and granular cytoplasm
- flexible to allow them to surround pathogens and engulf the
- contain lysosomes filled with lysozyme (hydrolytic enzyme)
- made from stem cells in bone marrow
describe the structure and function of sperm cells
- flagellum contains many mitochondria to release energy for locomotion which enables sperm cell to move towards egg cell
- acrosome in head contains digestive enzymes to digest egg cell wall so sperm can penetrate and fertilise egg cell wall
describe the structure and function of palisade cells
- located in mesophyll tissue layer of leaves
- rectangular in shape, tightly packed cells that contain lots of chloroplasts to absorb and maximise light energy for photosynthesis
- thin cell walls to reduce diffusion distance of carbon dioxide
describe the structure and function of guard cells
- pair of cells with flexible walls (more so on one side) which results in the cells bending when turgid to open stomata and closing when flaccid, this helps to control water loss by transpiration
describe the structure and function of root hair cells
- on the surface of roots
- long projections to to increase surface area for osmosis and active transport of mineral ions
- thin cell wall to reduce diffusion distance
what are the six types of tissue we need to know?
- squamous epithelia
- ciliated epithelia
- cartilage
- muscle
- xylem
- phloem
describe the structure of squamous epithelia.
- usually only a single layer or flat squamous cells in contact with basement membrane of the epithelium, providing a short diffusion distance
describe the structure of ciliated epithelia
- made of ciliated epithelial cells
- have hair-like projections that sway to move substances
- goblet cells also located within the epithelium, release mucus to trap molecules
describe the structure of cartilage
- connective tissue that’s firm and flexible
- provides structural support and prevent bones from rubbing togther and damaging themselves
- made of elastin and collagen fibres and chondrocyte cells within an extracellular matrix
describe the structure of muscle
- made up of tissues that can contract and relax, creating movement
- skeletal muscles cause the skeleton to move and are made up of myofibrils containing the proteins actin and myosin
- smooth muscle located within organs and cardiac muscle
- have multiple fibres connecting with connective tissue in between
describe the structure of xylem
- cells that make up the part of the vascular bundle in plants responsible for transporting water and mineral ions
- made up of elongated, hollow, dead cells, with lignin in the walls to strengthen and waterproof the walls
- made from the stem cells in the meristem
describe the structure of phloem
- cells that make up part of the vascular bundle responsible for transporting organic substances made in photosynthesis
- made of sieve tube element cells that have perforated end walls and are lacking most organelles to make transport of sugars easier, and companion cells which contain organelles to provide resources for the sieve tube elements
- phloem sieve tubes made of stem cells in meristem
what are stem cells? what are the different types? why are there different types of stem cells?
- undifferentiated cells that can self- renew (continually divide) and become specialised
the different types are:
- totipotent
- pluripotent
- multipotent
- unipotent
- because they have different differentiation abilities
describe totipotent stem cells.
- can divide and produce any type of body cell
- when developing they can only translate part of their DNA, allowing cell specialisation
- only occur for a limited amount of time in early mammalian embryos
- later develop into pluripotent cells
describe pluripotent stem cells.
- found in embryos
- can become almost any type of cell (can’t form the placenta)
- used in research with prospect of using them to treat human disorders
- issues: sometimes treatment dosent work, or stem cells continually divide, creating tumours
- ethical issues:ethical debate on whether it’s right to make a therapeutic clone of a patient to make an embryo genetically identical to them to get the stem cells to cure a disease and then destroy it
describe multipotent and unipotent cells.
- multi and unipotent cells are found in mature mammals and can divide into a limited number of different cell types
- multipotent cells (like in bone marrow) can differentiate into a limited number or cells
- unipotent cells can only differentiate into one type of cell
what are the potential uses of stem cells?
- could be used in both research and medicine, including:
- repairing damaged tissues
- treatment of neurological conditions like Alzheimer’s and Parkinson’s
- research into developmental biology
