6 - Cell division Flashcards
what is the cell cycle?
- the process that all body cells in multicellular organisms use to grow and divide.
- series of stages for a cell to divide into 2 genetically identical daughter cells.
- starts with one cell already produced by cell division and ends with 2 genetically identical daughter cells being produced.
what are the functions of the cell cycle?
- growth of tissue/organism.
- replacement of worn out/damaged cells.
- to repair damaged tissues.
- asexual reproduction in plants, animals, fungi
end products of cell cycle is?
2 genetically identical daughter cells.
stages of cell cycle:
- interphase: G1 phase (G1 checkpoint) S phase G2 phase (G2 checkpoint) - mitotic phase: mitosis cytokinesis
G1 phase?
- first growth phase
- synthesis of proteins
- organelles replicate
- cell increases in size
S phase?
- synthesis phase
- each chromosome is replicated in the nucleus
G2 phase?
- second growth phase
- cell continues to grow in size.
- energy stores increase
- duplicated DNA checked for errors
- proteins needed for cell division are needed.
mitosis?
the nucleus divides
cytokinesis?
the cytoplasm divides and two cells are produced.
How is the cell regulated?
- by checkpoints.
they monitor and verify whether the processes at each phase of the cell cycle have been accurately completed before moving onto the next.
G1 checkpoint
checks for:
- cell size
- nutrients
- growth factors
- DNA damage
G2 checkpoint
checks for
- cell size
- DNA replication
- DNA damage
spindle assembly checkpoint
checks for:
- chromosome attachment to spindle.
G0
- phase when cell leaves the cycle temporarily or permanently
- differentiation
- DNA damage
- as you age, no. of cells that enter G0 increase.
what are the stages of mitosis?
- prophase
- metaphase
- anaphase
- telophase
PMAT
Prophase
- chromosomes condense and thicken (become visible)
- each chromosome consists of 2 sister chromatids joined at centromere.
- two centrioles move to opposite poles of cell.
- spindle fibres attach to specific areas on centromeres and start to move chromosomes to equator of the cell.
- nuclear envelope disappears.
Metaphase
- individual chromosomes are moved by spindle fibres to align at equator of cell.
- chromosomes are attached to the spindle fibres by the centromere.
Anaphase
- centromeres holding the pairs of chromatids in each chromosome divide.
- spindle fibres contract
- each chromatid is pulled by their centromere to opposite sides of the cell.
Telophase
- chromatids reach opposite sides of the cell
- chromatids uncoil and become long and thin again.
- they are now called chromosomes (each chromosome now consists of one chromatid).
- spindle fibres disappear
- nuclear envelope reforms and enclose around the chromosomes at each pole.
Cytokinesis
- cytoplasm divides.
- in animal cells, a cleavage furrow forms to divide the cell surface membrane.
- forms 2 genetically identical daughter cells.
- begins in anaphase, ends in telophase.
- separate process to mitosis.
no of chromatids in the stages of cell division?
- one chromatid per chromosome before replication.
- two chromatids per chromosome after replication
- one chromatid per chromosome after mitotic division.
cytokinesis in plant cells?
- cell plate forms, 2 genetically identical daughter cells are formed.
what are homologous chromosomes?
homologous pair of chromosomes contain one maternal and one paternal chromatid.
same genes but different alleles.
What is meiosis?
the process by which sex cells (gametes) are made in the reproductive organs.
Importance of meiosis?
- gametes are produced
- promotes genetic variation in offspring.
- promotes genetic variation and allows for natural selection to take place.
How does genetic variation occur in meiosis?
- crossing over in prophase 1
- independent assortment in metaphase 1
why are gametes haploid?
- they only have one copy of each chromosome
- 23 chromosomes
- haploid
why are body cells diploid?
- they have two of each chromosome
- 46 chromosomes (23 pairs)
- diploid.
Which cells are diploid and haploid?
gametes: haploid
somatic (body) cells: diploid.
what are the stages of meiosis?
- interphase
- meiosis 1 prophase 1 metaphase 1 anaphase 1 telophase 1
- meiosis 2 prophase 2 metaphase 2 anaphase 2 telophase 2
interphase (meiosis)
- DNA unravels and replicates to produce sister chromatids.
prophase 1
- chromosomes condense
- nuclear envelope dissolves
- homologous chromosomes form bivalents.
- centrioles move to opposite poles of cell.
- crossing over occurs
- chiasmata form between non-sister chromatids of homologous chromosomes.
- chromatids have same genes, different combination of alleles.
metaphase 1
- spindle fibres from opposing centrioles connect to bivalents (at centromeres) and align along equator of cell.
- independent assortment occurs
- orientation of each homologous pair is random and independent to any other homologous pair.
anaphase 1
- spindle fibres contract
- bivalent splits
- homologous chromosomes move to opposite poles of the cell
telophase 1
- chromosomes decondense
- nuclear envelope may reform
- cytokinesis occurs to form 2 haploid daughter cells.
prophase 2
- chromosomes condense
- nuclear envelope dissolves
- centrioles move to opposite poles of cell.
- spindle fibres reform.
metaphase 2
- spindle fibres from opposing centrioles attach to chromosomes at centromere and align them along equator of cell.
anaphase 2
- spindle fibres contract
- sister chromatids separate
- chromatids (now called chromosomes) move to opposite poles of cell.
telophase 2
- chromosomes decondense
- spindle fibres breaks down
- nuclear envelope reforms.
- cell undergoes cytokinesis
- cytoplasm and cell surface membrane divide, forming ↓
- 4 independent haploid daughter cells.
What is the product of meiosis?
- 4 haploid daughter cells.
- gametes.
What are specialised cells?
- cells which are differentiated, meaning that they are specialised to carry out very specific functions.
erythrocytes
- transports oxygen around the body.
- biconcave shape (increases surface area to vol ratio).
- no nucleus/other organelles. Increases space for available for haemoglobin.
- flexible: able to squeeze through narrow capillaries.
neutrophils
- essential role in immune system.
- multi-lobed nucleus gives them flexibility
- granular cytoplasm contains lots of lysosomes that contain hydrolytic enzymes that attack pathogens.
squamous cells
- very thin cells
- provides a short diffusion distance for efficient diffusion of gases.
ciliated epithelial cells
- cilia
- wafts particles.
sperm cells
- function to deliver genetic information to egg cell.
- flagellum so they can swim to the egg cell.
- lots of mitochondria to provide energy to swim.
- acrosome contains digestive enzymes, so they can penetrate the surface of the egg.
palisade cells
- present in mesophyll
- majority of photosynthesis occurs here.
- Lots of chloroplasts, photosynthesis levels are high here.
- rectangular shape to form a continuous layer.
- thin cell walls, increases rate of diffusion of CO2.
- chloroplasts can move within the cytoplasm to absorb more light.
- large vacuole maintains turgor pressure.
Root hair cells
- absorbs water and mineral ions from soil.
- large surface area maximises uptake of water and mineral ions.
- thin cell wall, increases rate of absorption.
- lots of mitochondria provides energy for active transport.
guard cells
- found in pairs with a gap called stoma.
- when guard cells are turgid, stomata opens.
- when guard cells are flaccid, stomata closes.
- thick inner wall, thin outer wall causes them to bend outwards when turgid.
What is a tissue?
A tissue is a group of differentiated cells that work together to perform a particular function.
squamous epithelium
- single layer of flat cells lining a surface.
- present when rapid diffusion across a surface is essential.
- found in alveoli in lungs.
- ## provides a short diffusion distance, allowing a high rate of diffusion of gases in the alveoli.
ciliated epithelium
- has hair-like structures called cilia.
- in trachea, goblet cells are also present which secrete mucus. Cilia waft the mucus away from the lungs to the back of the throat.
- prevents microorganisms from reaching alveoli in lungs.
cartilage
- connective tissue found in joints, outer ear, nose.
- firm flexible connetive tissue composed of chondrocyte cells in an extracellular matrix.
- prevents end of bones from rubbing together.
Muscle
- tissue that contracts to move bones, which moves different parts of the body.
- made up of bundles of muscle fibres.
- muscle fibres separated by connective tissue.
- smooth
- cardiac
- skeletal
xylem
- plant tissue
- transports water and minerals throughout plants.
- provides structural support
- travel direction is upwards only.
- xylem vessel elements which are elongated dead cells.
- living parenchyma cells.
- lignin in xylem tissue provides structural support for plants.
phloem
- plant tissue
- transports organic solutes such as sucrose from leaves to rest of plant.
- travel direction is bidirectional.
- composed of sieve tube elements, separated by sieve plates (lets phloem content flow through).
What is an organ?
- a group of different tissues that work together to perform a specific function.
examples of organs?
- lungs
- contains squamous epithelial tissue, ciliated epithelial tissue.
- elastic connective tissue and vascular tissue in blood vessels.
- leaves
- palisade tissue (photosynthesis)
- epidermal tissue (prevent water loss)
- xylem and phloem tissue.
What are organ systems?
They are systems in which organs work together to perform a specific function.
examples of organ systems?
- digestive system
- cardiovascular system
- gaseous exchange system.
What is a stem cell?
a renewing source of undifferentiated cells. They have a potential to become specialised.
Where are embryonic stem cells found?
blastocyst
order of potency of stem cells? from least potent?
- unipotent
- multipotent
- pluripotent
- totipotent
potency of embryonic stem cells?
totipotent for 7 days after start of embryo development and pluripotent after the blastocyst forms.
- they can differentiate into almost every cell type under the correct lab conditions.
Replacement of red and white blood cells using stem cells?
- adult stem cells in the bone marrow.
- they differentiate to replace worn out erythrocytes and neutrophils.
Where are stem cells present in plants?
meristems
What do stem cells in plants differentiate into?
stem cells in the meristems in the vascular cambium of plants differentiate into xylem vessels and phloem sieve tubes.
stem cells for treating burns?
- stem cells can be used to create skin grafts to treat burns.
stem cells for treating Alzheimer’s?
- nerve cells die in increasing numbers.
- hope to use stem cells to regrow healthy nerve cells
stem cells for treating Parkinson’s’?
- caused by death of dopamine-producing cells in the brain.
- stem cells may help to regenerate the dopamine-producing cells.
research into developmental biology?
- stem cells can be used to research about how organisms grow and develop.
- can help us to understand more about developmental disorders and cancer.
