Module 2.6 - Cell Division, Cell Diversity And Cell Differentiation Flashcards
(MA) Describe the organisation of cells in a multicellular organism.
- Cells differentiate
- Groups of similar specialised cells working together to perform a common function form tissues
- Groups of tissues working together form organs
- Groups of organs working together form organ systems
(MA) What happens during the interphase of the cell cycle?
- Made up of G1, S + G2 phases
- G1: cell grows, respires, proteins made + organelles replicated
- S: DNA replication occurs, chromosomes become sister chromatids joined by centromere
- G2: DNA replication checked for mistakes, organelles replicated
(MA) What happens during the cytokinesis phase of the cell cycle?
- Cytoplasm cleaves down furrow to split cytoplasm
- Produces 2 new genetically identical daughter cells (also genetically identical to parent cell)
(MA) Describe the stages of mitosis.
-Prophase:
> Sister chromatids supercoil to shorten + thicken
> Sister chromatids now consist of sister chromatids joined by a centromere
> Now visible under a light microscope
> Nuclear envelope breaks down
> Centriole divides in 2 + each daughter centrioles goes to a pole of the cell
> Spindle fibres (microtubules) begin to form
-Metaphase:
> Sister chromatids line up along equator
> Spindle fibres attach to centromeres
-Anaphase:
> Centromere splits
> Chromatids separate
> Spindle fibres shorten
> Pull identical chromatids so they move to opposite poles with the centromere leading
-Telophase:
> Chromosomes uncoil
> Nuclear envelope reforms
> Spindle fibres break down
(MA) Compare mitosis and meiosis.
-Mitosis produces 2 genetically identical diploid daughter cells used for growth + repair (+ asexual reproduction). Occurs in all body cells. 1 division
-Meiosis: produces 4 genetically different haploid daughter cells. Used for producing gametes. Only occurs in ovaries + testes. 2 divisions
(-Both start from a single parent cell)
(MA) Describe the cell division and budding in yeast cells.
- Nuclei divided by mitosis
- Bulge in surface of cell
- Nucleus moves to bulge
- Bulge nips / pinches off
- Leaves an uneven distribution of cytoplasm in the 2 cells
(MA) Describe the structure and function of erythrocytes as specialised cells.
- No nucleus or many other organelles e.g. Golgi, mitochondria + ER, max space for Hb to increase O2 carrying capacity
- No nucleus + organelles make more flexible to fit through capillaries
- Filled w Hb that can bind w O2 to form oxyHb to transport it round to aerobically respiring cells
- Biconcave disc shape to provide larger SA:vol ratio for O2 exchange for more efficient O2 uptake into RBCs
(MA) Describe the structure and function of root hair cells as specialised cells.
- Hair like projection into soil for large SA for osmosis + mineral uptake (active transport) into roots
- Thin walk for short diffusion path
- Many mitochondria to provide energy for active transport of minerals
- Many carrier proteins for active transport of minerals
- Many channel proteins for uptake of water via osmosis
(MA) Describe the structure and function of neutrophils (phagocytes) as specialised cells.
- Contain lots of lysosomes containing lysine enzymes to digest pathogens
- Multi-lobed nucleus to fit between gals in endothelial cells of capillaries to leave blood
- Contain many mitochondria to move lysosomes + phagosomes through cell along microtubules
(MA) Describe the structure and function of sperm as a specialised cell.
- Haploid nucleus so when it fertilises an egg, the zygote diploid
- Many mitochondria to provide energy for movement of flagellum
- Shape: long + thing - ease of movement
- Enzyme contained in acrosome so when sperm meets egg it can penetrate it to fertilise it
What are the two main checkpoints during the cell cycle?
- G1/S checkpoint (restriction point)
- G2/M checkpoint
What is the purpose of checkpoints during the cell cycle?
- Prevent uncontrolled decision that’d lead to tumours (cancers)
- Detect + repair damage to DNA (e.g. damage by UV light)
- Ensures cycle can’t be reversed
- Ensures DNA can only be replicated once during each cell cycle
What occurs during the G1 phase of interphase?
- G1 checkpoint ensures cell ready to enter S phase + begin DNA synthesis
- Cells grow + increase in size
- Transcription of genes to make RNA
- Organelles duplicate
- Biosynthesis e.g. protein synthesis incl making enzymes needed for DNA replication in S phase
- p53 (tumour suppressor) gene helps control this phase
What occurs during the S phase of interphase?
- As chromosomes unwound + DNA diffuse, every molecule of DNA replicated. Specific sequence to gene replication: housekeeping genes (active in all cells) duplicated first. Genes normally inactive in specific cells replicated last
- Once cell enters this phase, committed to completing cell cycle
- DNA replicates
- When all chromosomes duplicated, each one consists of a pair of identical sister chromatids
- Phase is rapid, as exposed DNA base pairs are more susceptible to mutagenic agents. Reduces chances of spontaneous mutations
What occurs during the G2 phase of interphase?
- Special chemicals ensure cell ready for mitosis by stimulating proteins involved in making chromosomes condense + formation of spindle
- Cell grows
What is mitosis used for?
- Asexual reproduction
- Growth
- Tissue repair
Describe the events in the prophase phase of mitosis.
- Replicated chromosomes (from S of interphase) + consist of identical sister chromatids, now shorten + thicken as DNA supercoils
- Nuclear envelope breaks down
- Centriole in animal cells (in centrosome) divides + 2 new daughter centrioles move to opposite poles of cell
- Cytoskeleton protein (tubulin) threads form spindle between centrioles. Spindle: 3D structure. In plants, tubulin threads formed from the cytoplasm
Describe the events in the metaphase phase of mitosis.
- Pair of chromatids attach to spindle threads at equator region
- Attach by their centromeres
Describe the events in the anaphase phase of mitosis.
- Centromere of each pair of chromatids splits
- Motor proteins, walking along tubulin threads, pull each sister chromatid of a pair, in opposite directions towards opposite poles
- As centromere leads, chromatids (now called chromosomes) assume a V shape
Describe the events in the telophase phase of mitosis.
- Separated chromosomes reach poles
- Nuclear envelope forms around each set of chromosomes
- Cell now contains 2 nuclei each genetically identical to each other + parent cell from which they arose
What is the purpose of meiosis?
-Increases genetic variation (due to fertilisation)
What are homologous chromosomes?
- Matching chromosomes, containing same genes at same places. May contain different alleles for some genes
- Matching pairs one maternal + one paternal chromosome
Describe the events in prophase 1 of meiosis.
- Chromatin condenses + each chromosome supercoils. Can now take up stains + be seen w a light microscope
- Nuclear envelope breaks down + spindle threads of tubulin protein form from centriole in animal cells
- Chromosomes come together in their homologous pairs
- Each member of the pair consists of 2 chromatids
- Crossing over occurs when non-sister chromatids wrap around each other + may swap sections so alleles are shuffled
Describe the events in metaphase 1 of meiosis.
- Pairs of homologous chromosomes, still in crossed over state, attach along equator of spindle
- Each attaches to a spindle thread by its centromere
- Homologous pairs are arranged randomly, with members of each pair facing opposite poles of cell. Arrangement = independent assortment
- The way they line up in metaphase determines how they’ll segregate independently when pulled apart during anaphase
Describe the events in anaphase 1 of meiosis.
- Members of each pair of homologous chromosomes are pulled apart by motor proteins that drag them along tubulin threads of spindle
- Centromeres don’t divide + each chromosome consists of 2 chromatids
- Crossed over areas separate from each other, resulting in swapped areas of chromosomes + allele shuffling
Describe the events in telophase 1 of meiosis.
- Most animal cells: 2 nuclear envelopes form around each set of chromosomes + cell divides by cytokinesis. There’s then short interphase when chromosomes uncoil
- Each new nucleus contains half no. of chromosomes, but each chromosome consist of 2 chromatids
- Most plant cells: cell goes straight from anaphase 1 to prophase 2
Describe the events in prophase 2 in meiosis.
- If nuclear envelopes have reformed, they break down again
- Chromosomes coil + condense, each one consisting of 2 chromatids
- Chromatids of each chromosome no longer identical, due to prophase 1’s crossing over
- Spindles form
Describe the events in metaphase 2 in meiosis.
- Chromosomes attach by their centromere to equator of spindle
- Chromatids of each chromosome are randomly arranged
- Way they’re arranged determines how the chromatids separate during anaphase
Describe the events during anaphase 2 in meiosis.
- Centromeres divide
- Chromatids of each chromosome pulled apart by motor proteins that drag them along tubulin threads of spindle, towards opposite poles
- Chromosomes therefore randomly segregated
Describe the events during telophase 2 in meiosis.
- Nuclear envelopes form around each of the 4 haploid nuclei
- Animals: the 2 cells now divide to give 4 haploid cells
- Plants: tetrad of 4 haploid cells is formed
How does meiosis produce genetic variation?
- Crossing over (prophase 1)
- Independent assortment of chromosomes (anaphase 1) leads to random distribution of maternal + paternal chromosomes in each pair
- Independent assortment of chromatids (anaphase 2) leads to further random distribution of genetic material
- Haploid gametes are produced, which can undergo random fusion w gametes derived from another organism of the same species
Give some examples of what may change when an undifferentiated cell (e.g. embryonic stem cells).
- Proportions of different organelles
- Shape of cell
- Some of the cell’s contents
How are erythrocytes specialised to their function?
- V small (7.5μm diameter) so large SA:vol ratio so O2 can diffuse across membranes + easily all regions inside cell. Biconcave shape also increases SA:vol ratio
- Flexible: well developed cytoskeleton allows erythrocytes to change shape so can twist + turn as they travel through narrow capillaries
- Most organelles lost at differentiation so no nucleus, mitochondria or ER + little cytoplasm. More space for many Hb molecules. Hb synthesised within immature RBCs, when still have nucleus, ribosomes + ER
How are neutrophils specialised to their function?
- Twice size of erythrocytes + each neutrophil contains a multilobed nucleus
- Attracted to + travel towards infection site by chemotaxis
- Function: ingest bacteria + some fungi by phagocytosis
How are spermatozoa specialised to their function?
- Many mitochondria for aerobic respiration providing ATP for undulipodium to move + propel cell towards ovum
- Long + thin so can move easily
- Once sperm reaches ovum, enzymes are released from acrosome (specialised lysosome). Enzymes digest outer protective covering of ovum allowing sperm head to enter ovum
- Head of sperm contains haploid gamete nucleus + very little cytoplasm
How are epithelial cells specialised to their function?
(-Lining tissue)
- Squamous epithelial cells: flattened in shape
- Many cells of epithelium have cilia
What are palisade cells specialised for and how are they specialised to carry out this function?
- Photosynthesis
- Long + cylindrical so pack together quite closely but w a little space between them for air to circulate, CO2 in these air spaces diffuses into cells
- Large vacuole so chloroplasts are near periphery of cell reducing diffusion distance for CO2
- Contain many chloroplasts
- Contain cytoskeleton threads + motor proteins to move chloroplasts nearer to upper surface of leaf when light intensity low + further down when high
How are guard cells adapted to their function?
- Light energy used to produce ATP
- ATP actively transports K+ ions from surrounding epidermal cells into guard cells, lowering water potential
- Water now enters guard cells from neighbouring epidermal cells by osmosis
- Guard cells swell but at tips cellulose wall is more flexible + more rigid when thicker. Tips bulge + gaps between them (stoma) enlarge
- As stomata open, air enters spaces within layer of cells beneath palisade cells
- Gaseous exchange can occur + CO2 will diffuse into palisade cells. As they use it for photosynthesis a steep conc grad maintained
- O2 produced during photosynthesis can diffuse out of palisade cells into air spaces + through open stomata (when stomata open, water vapour also exits from them)
How are root hair cells adapted to their function?
- Hair like projections greatly increase SA for water absorption + mineral ions (e.g. nitrates) from soil
- Mineral ions actively transported into RHCs lowering water potential causing water to follow via osmosis down water potential gradient
- Have special carrier proteins in plasma membranes to actively transport in mineral ions
- Also produce ATP needed for active transport
What are the four types of tissue types?
- Epithelial tissue (lining tissue)
- Connective tissues (hold structures together + provide support e.g. blood, bone, catilage)
- Muscle tissue (made of cells specialised to contract + cause movement)
- Nervous tissue (made of cells specialised to conduct electrical impulses)
What are the characteristics of epithelial tissue?
- Made up almost entirely of cells
- Cells v close to each other + form continuous sheets. Adjacent cells bound together by lateral contacts (e.g. tight junctions + desmosomes)
- No blood vessels, retrieve nutrients by diffusion from tissue fluid in underlying connective tissue
- Some have smooth surfaces but some have projections (cilia or microvilli)
- Have short cycles + divide up to 2 or 3 times a day to replace worn/damaged tissue
- Specialised to carry out functions of protection, absorption, filtration, excretion + secretion
What is the make up connective tissue?
- Non living extra cellular matrix containing proteins (collagen + elastin) + polysaccharides (hyaluronic acid that traps water)
- Matrix separates living cells within tissue + enables it to withstand forces e.g. weight
What are some examples of connective tissue?
- Blood
- Bone
- Cartilage
- Tendons
- Ligaments
- Skin also contains connective tissue
What are the main types of muscle tissue?
- Skeletal muscle: packaged by connective tissue sheets, joined to bones by tendons. When contract, cause bones to move
- Cardiac muscle: make up walls of heart + allows heart to beat + pump blood
- Smooth muscle: occurs in intestine walls, blood vessels, uterus, urinary tracts + propels substances along these tracts
Where are meristematic cells found?
- Root + shoot tips
- Cambium of vascular bundles
Describe the cells that make up meristematic tissue.
- Thin walks containing v little cellulose
- No chloroplasts
- Don’t have a large vacuole
- Can divide by mitosis + differentiate into other cell types
How do cambium cells differentiate into xylem vessels?
- Lignin deposited in cell walls to reinforce + waterproof (kills the cells)
- Ends break down so xylem forms continuous columns w wide lumens to carry water + dissolved minerals
How do cambium cells differentiate into phloem sieve tubes or companion cells?
- Sieve tubes lose most their organelles + sieve plates develop between them
- Companion cells retain organelles + continue metabolic functions to provide ATP for active loading of sugars into sieve tubes
Give some examples of organs in plants and their functions.
- Leaf: photosynthesis
- Root: anchorage in soil, absorption of mineral ions + water, storage (e.g carrot, parsnip, dahlia, swede roots store carbohydrates)
- Stem: support, holds leaves up so expose to more sunlight, transportation of water + minerals + products of photosynthesis, storage of products of photosynthesis (potato tubers store starch, rhubarb stems store sugars + polysaccharides)
- Flower: sexual reproduction
What are the tissues and organs involved in the digestive system and what examples of life processes are carried out in this system?
- Oesophagus, stomach, intestines + associated glands, liver + pancreas
- Nutrition to provide ATP materials for growth + repair
What are the tissues and organs involved in the circulatory system and what examples of life processes are carried out in this system?
- Heart + blood vessels
- Transport to + from cells
What are the tissues and organs involved in the respiratory system and what examples of life processes are carried out in this system?
- Airways + lungs, diaphragm + intercostal muscles
- Breathing + gaseous exchange excretion
What are the tissues and organs involved in the urinary system and what examples of life processes are carried out in this system?
- Kidneys, uterus, bladder
- Excretion + osmoregulation
What are the tissues and organs involved in the integumentary system and what examples of life processes are carried out in this system?
- Skin, hair, nails
- Waterproofing, protection, temperature regulation
What are the tissues and organs involved in the musculo-skeletal system and what examples of life processes are carried out in this system?
- Skeleton + skeletal muscles
- Support, protection + movement
What are the tissues and organs involved in the immune system and what examples of life processes are carried out in this system?
- Bone narrow, thymus gland, skin, stomach acid, blood
- Protection against pathogens
What are the tissues and organs involved in the nervous system and what examples of life processes are carried out in this system?
- Brain, spinal cord, nerves
- Communication, control + coordination
What are the tissues and organs involved in the endocrine system and what examples of life processes are carried out in this system?
- Glands that make hormones e.g thyroid, ovaries, testes, adrenals
- Communication, control + coordination
What are the tissues and organs involved in the reproductive system and what examples of life processes are carried out in this system?
- Testes, penis, ovaries, uterus, vagina
- Reproduction
What are the tissues and organs involved in the lymph system and what examples of life processes are carried out in this system?
- Lymph node + vessels
- Transports fluid hack to circulatory system + also important in resisting infections
Describe what stem cells are.
- Undifferentiated cells, capable of becoming any type of cell in the organism
- Pluripotent
- Able to express all their genes
- Can divide by mitosis + provide more cells that can then differentiate into specialised cells, for growth + tissue repair
What are the sources of stem cells?
- Embryonic stem cells: present in early embryo formed when zygote begins to divide
- Stem cells in umbilical cord
- Adult stem cells: found in developed tissues (blood, brain, muscle, bone, adipose tissue + skin). Act like repair system as renew source of undifferentiated cells
- Induced pluripotent stem cells (iPS cells): developed in labs by reprogramming differentiated cells to switch on certain key genes + become differentiated
What are the potential uses of stem cells in research and medicine?
- Bone marrow transplants
- Drug research
- Developmental biology
- Repair of damages tissues or replacement of lost tissues
How can stem cells be used in bone marrow transplants?
- Treat diseases of blood (sickle cell anaemia + leukaemia) + immune system (severe combined immunodeficiency SCID)
- Used to restore patient’s blood system after treatment for specific types of cancer where bone marrow cells can be obtained before treatment, stores + put back inside patient after treatment
How are stem cells used in drug research?
-If stem cells can be made to develops into particular types of human tissue new drugs tested on these first rather than animal tissue
How are stem cells used in developmental biology?
- Can study how these cells make particular cell types (blood, bone, muscle + skin) + learn how each cell type functions + see what goes wrong when they’re diseased
- Trying to find out if can extend capacity embryons have for growth + tissue repair into later life
How are stem cells used to repair damaged tissues or replace lost tissues?
- Used to treat mice w type 1 diabetes by programming iPS cells to become pancreatic beta cells. Research under way to develop such treatment for type 1 diabetes in humans
- Bone marrow stem cells can be made to develop into liver cells (hepatocytes) + could be used to treat liver disease
- Directed to become nervous tissue could be used to treat Alzheimer + Parkinson diseases or repair spinal cord injuries
- May be used to populate bioscaffold of an organ + directed to develop + grow into specific organs for transplanting. Called regenerative medicine. If patient’s cells obtained, reprogrammed to become iPS cells + used to make such an organ there’ll be no need for immunosuppressant drugs
- May eventually be used to treat conditions (e.g. arthritis, strokes, burns, vision + hearing loss, Duchenne muscular dystrophy + heart disease
