Mod 2 Chap 6: Cell Division, Diversity & Differentiation Flashcards
Describe the cell cycle.🌟
- highly ordered sequence of events
- takes place in a cell, resulting in division of cell + formation of two genetically identical daughter cells
- has two main phases (in eukaryotes): interphase, and mitotic (division) phase (= mitosis / meiosis)
Generally describe Interphase.🌟
- long periods of growth and normal working separate divisions where a cell is NOT dividing
- although aka ‘resting phase’, interphase actually = a v active phase, when cell is carrying out all major functions e.g. Producing enzymes / hormones + preparing cell for division
- has three stages within itself: G1, S + G2
Describe what occurs in the stage of Interphase as a whole.🌟
- DNA replicated + checked for errors in nucleus
- protein synthesis occurs in cytoplasm
- mitochondria grow + divide in plant + agal cell cytoplasm
- normal metabolic processes of cells occur
Describe what occurs in the separate stages within Interphase.🌟
G1 (first growth phase): proteins from which organelles are synthesised are produced + organelles replicate, cell increases in size
S (synthesis phase): DNA replicated in nucleus
G2 (second growth phase): cell continues to increase in size, energy stores increase + duplication of DNA is checked for errors
Generally describe the mitotic phase.🌟
- period of cell division
- two stages of cell division: Mitosis (nucleus divides), and Cytokinesis (cytoplasm divides + two cells produced)
Describe the ‘G0’ phase of the cell cycle.
- phase where cell leaves the cycle (temporarily / permanently)
Reasons this happens:
- differentiation: a cell specialised to carry out a function is no longer able to divide, as carries out this function indefinitely + does not enter cycle again
- DNA of cell maybe damaged: meaning it’s no longer viable, damaged cells cannot divide and enters period of permanent cell arrest (G0), normal cells only divide limited no of times before becoming senescent
- age: ageing = no of senescent cells in body increasing, this then linked w/ age relating diseases e.g cancer / arthritis
Describe how the cell cycle is regulated / controlled.🌟
- needed to ensure a cell only divides when it has grown to right size, replicated DNA is correct + when chromosomes are in correct positions during mitosis, so to ensure fidelity of cell division (creation of tow identical daughter cells)
- control mechanisms of cell cycle = checkpoints
- checkpoints monitor whether each phase of cycle is accurately completed before cell progresses to next phase
- occur variously throughput cycle: end of G1 phase, end of G2 phase, + in mitosis
Describe the importance of mitosis.🌟
- mitosis = term for entire process of cell division in eukaryotic cells
- refers to nuclear division (essential stage in cell division)
- ensures both daughter cells produced are genetically identical, each new cell has an exact copy of DNA in parent cell + same no of chromosomes
- necessary for asexual reproduction (production or genetically identical offspring from one parent in multicellular organisms + eukaryotic single celled organisms. But prokaryotic organisms have no nucleus so reproduce asexually by diff process: binary fission.
Describe what happens with the chromosomes PRIOR to mitosis.🌟
- all DNA in nucleus has to be replicated in interphase before mitosis can occur
- each DNA molecule (chromosome) converted into two identical DNA molecules called chromatids
- two chromatids then join at region called centromere, so they can be precisely manoeuvred + segregated equally, one each into the two new daughter cells, during mitosis
Name the main stages of mitosis.🌟
4 stages:
- Prophase
- Metaphase
- Anaphase
- Telophase
Describe the Prophase stage of Mitosis.🌟
- chromatin fibres ( = mix of various proteins + DNA + RNA) coil + condense to form chromosomes
- nucleolus (area of nucleus responsible for RNA synthesis) disappears + nuclear membrane breaks down
- protein microtubules form spindle-shaped structures linking poles of cell
- in animal cells + some plant cells; two centrioles migrate to opposite poles of cell
- spindle fibres attach to specific areas on centromeres + move chromosomes to centre of cell
- nuclear envelope has disappeared now
Describe the Metaphase stage of Mitosis.🌟
- chromosomes moved by spindle fibres to form a plane in centre of cell, called metaphase plate, then held in position
Describe the Anaphase stage of Mitosis.🌟
- centromeres holding together chromatid pairs divide
- chromatids then separated + pulled to opposite poles of cell by shortening spindle fibres
- ‘V’ shape of chromatids moving towards poles is result of them being dragged by centromeres through the liquid cytosol
Describe the Telophase stage of Mitosis.🌟
- chromatids have now reached poles + now called chromosomes
- the two new sets of chromosomes assemble at each pole + nuclear envelope reforms around them
- chromosomes start to uncoil + nucleolus is formed
- cell division / cytokinesis begins
Generally describe Meiosis.🌟
- gametes are formed by meiosis
- nucleus (in meiosis) divides to produce 4 daughter cells (gametes)
- each gamete contains half of chromosome no. of parent cell (it is haploid)
- Meiosis known as reduction division
- each nucleus of organism’s cells contains two full sets of genes, so each nucleus gas matching set of chromosomes called homologous chromosomes + so is termed diploid
Describe alleles.
- Diff versions of same gene (aka gene variants)
- the diff alleles of a gene will all have same locus (position on a particular chromosome)
Name and outline the main stages of Meiosis.🌟
- Meiosis involves two divisions: Meiosis 1 and Meiosis 2, each has a single pro, meta, ana and telo phase
Meiosis 1:
- the reduction division where pairs of homologous chromosomes are separated into 2 cells
- each intermediate cell only has one full set of genes instead of 2, so cells are haploid
Meiosis 2:
- second division = similar to mitosis
- pairs of chromosomes present in each daughter cell are separated, forming 2 more cells
- so 4 haploid daughter cells produced in total
Describe the Prophase 1 stage of Meiosis 1.🌟
- chromosomes condense, nuclear envelope disintegrates, nucleolus disappears + spindle formation begins (all same as mitosis prophase)
- also homologous chromosomes pair up, forming bivalents
- chromosomes moving through liquid cytoplasm as they are brought together results in chromatids entangling = “crossing over”
Describe the Metaphase 1 stage of Meiosis 1.🌟
- same as metaphase in mitosis, except homologous Paris of chromosomes assemble along metaphase plate instead of individual chromosomes
- orientation of each homologous pair on metaphase plate = random + independent of any other homologous pair
- maternal / paternal chromosomes can end up facing either pole = called independent assortment, so can result in many diff combinations of alleles facing poles
- independent assortment of chromosomes in Metaphase 1 results in genetic variation.
Describe the Anaphase 1 stage of Meiosis 1.🌟
- diff from anaphase of mitosis as homologous chromosomes are pulled to opposite poles + chromatids stay joined together
- sections of DNA on entangled ‘sister’ chromatids now break off + rejoin, which can cause an exchange of DNA
- points at which chromatids break + rejoin = chiasmata
- when exchange occurs, recombinant chromatids form, genes exchanged between chromatids
- genes exchanged may be diff alleles of same gene, so combination” of alleles on recombinant chromatids will be diff from allele combination on either of original chromatids
- this new combination of alleles makes genetic variation, sister chromatids are no longer identical
Describe the Telophase 1 stage of Meiosis 1.🌟
- essentially same as in mitosis, chromosomes assemble at each pole + nuclear membrane reforms, chromosomes uncoil
- cell undergoes cytokinesis + divides into 2 cells
- reduction of chromosome number from diploid to haploid is complete
Describe the Prophase 2 stage of Meiosis 2.🌟
- chromosomes that still consist of two chromatids condense + become visible again
- nuclear envelope breaks down + spindle formation begins
Describe the Metaphase 2 stage of Meiosis 2.🌟
- differs from metaphase 1, as individual chromosomes assemble on metaphase plate, as in metaphase in mitosis
- due to crossing over, chromatids no longer identical so there is independent assortment again + more genetic variation produced in metaphase 2
Describe the Anaphase 2 stage of Meiosis 2.🌟
- unlike anaphase 1, 2 results in chromatids of individual chromosomes being pulled to opposite poles after division of centromeres - same as anaphase of mitosis.
Describe the Telophase 2 stage of Meiosis 2.🌟
- chromatids assemble at poles (as in mitosis telophase)
- chromatids uncoil + form chromatin again
- nuclear envelope reforms + nucleolus becomes visible
- cytokinesis results in division of cells forming 4 daughter cells in total, which will be haploid, due to reduction division, + will aslo be genetically diff from each other + from parent cell, due to crossing over + independent assortment
Describe the specialised animal cell Erythrocytes, their role and how they are fit for this function.🌟
Produced: in bone marrow (soft, highly cellular tissue)
Role: transport O2 around body to respiring cells + carry CO2 from respiring cells to lungs for ventilation
How they are fit for their function:
- biconcave shape increases SA:V ratio of cell
- no nucleus / organelles = more space in cell for haemoglobin so each cell can carry more O2
- flexible so able to squeeze through narrow capillaries
Describe the specialised animal tissue Ciliated Epithelium.🌟
- made up of Ciliated epithelial cells that have a hair like structure called cilia on their surface
- these beat to move particles away from cells to prevent build of particles in areas that would cause infection
- contains goblet cells that secrete mucus to trap unwanted particles
Describe the specialised animal tissue Squamous Epithelium.🌟
- made up of specialised squamous epithelial cells
- made up of thin, flat cells bound tightly together + is only one cell thick
- this allows diffusion to occur at faster rate due to short diffusion distance
- is present when rapid diffusion across a surface is essential
Describe the specialised animal cell Neutrophils, their role and how they are fit for this function.🌟
Produced: by stem cells in bone marrow
Role:
- kill microorganisms w/ antimicrobial effectors
- are first cells to migrate to site of infection
- keep things under control until immune system kicks in
- destroy foreign bodies by engulfing them (phagocytosis) and secreting enzymes
How they are fit for their function:
- multi-lobed nucleus allows easier squeezing through gaps to get to infection site
- granular cytoplasm has lysosomes containing enzymes to attack pathogens
- attracted to side of infection by chemical messengers
Describe the specialised animal cell Spermatozoa (sperm cells), their role and their structure.🌟
Produced: in male sex organs (testes) in the seminiferous tubules
Role:
- are the male gametes responsible for delivering genetic information to female gamete (egg cell), in fertilisation
Structure:
- tail (flagellum) allows movement
- have mitochondria in mid piece supplying them w/ energy to swim
- head contains haploid nucleus = important when gametes fuse, forming a diploid nucleus in zygote
- acrosome on head has digestive enzymes released to digest protective layers around ovum + allow penetration for sperm, leading to fertilisation
Describe the specialised plant cell Root Hair Cells, their roles and their structure.🌟
Role: to absorb water + minerals in the soil, to be transported in translocation + transpiration
Structure:
- large SA due to hair like projections that maximise water uptake + minerals
- many mitochondria = maximises energy available for active transport to absorb minerals
- cellulose cell wall = creates shorter diffusion distance
- vacuoles containing cell sap which decreases water potential, creating a steep gradient so increased rate of osmosis
- have carrier proteins in cell membrane to aid uptake of ions from soil
Describe the specialised plant cell Palisade Cells, their role, location and their structure.🌟
Location: within mesophyll below up over epidermis
Role:
- contain chloroplasts to absorb large amounts of light for photosynthesis
Structure:
- vertically elongated like a rectangular box shape allowing them to be closely packed to form a continuous layer
- have a thin cell wall, increasing rate of diffusion of CO2
- have a large vacuole = maintains turgor pressure
- have many chloroplasts that can move within cytoplasm to absorb more light
Describe the specialised plant tissue Xylem Tissue, it’s role and its structure.🌟
Role: transport water + mineral ions, + to support rest of plant
Structure:
- type of vascular tissue
- composed of vessel elements which are elongated dead cells w/ waterproof material called lignin in their walls = provides structural support
- vessel has bordered pits = allows water to leave at certain points
Describe the specialised plant tissue Phloem Tissue, it’s role and its structure.🌟
Role: transports food in form of organic solutes / nutrients (particularly sucrose) around plant, from leaves + stems to everywhere needed
Structure:
- type of vascular tissue
- made of cells joined end to end forming a hollow tube structure
- sieve plates act as pores between end to end cells = allow phloem contents to flow through
- companion cells linked to sieve tube by plasmodesmata that still contain all organelles, allowing them to control functions of sieve tube elements
- sieve tubes use companion cells to load sucrose
Describe the specialised plant cells Guard Cells, their role and their structure.🌟
Role: control the opening and closing if stomata + so control rate of transpiration in plants
- stomata necessary for CO2 to enter plants for photosynthesis
Structure:
- contain cellulose hoops = prevent cell from swelling in width when becomes turgid
- thicker inner wall which is less flexible than thinner outer wall = cause cell to expand outwards into a c-shape, so opening stomata
- are only cells on lower side of leaf w/ chloroplasts = allows them to detect presence of light + so know when to open + close stomata
State the levels of organisation in multicellular organisms.🌟
Specialised cells ⬇️ Tissues ⬇️ Organs ⬇️ Organ systems ⬇️ Whole organism
Describe the organisation of cells into tissues.🌟
- a tissue = made up of a collection of differentiated cells w/ a specialised function / function
- so each tissue adapted for a particular function in an organism
Name the four main categories of tissues in animals and their adaptions to function.🌟
- nervous tissue: adapted to support transmission of electrical impulses
- epithelial tissue: adapted to cover body surfaces (internal + external)
- muscle tissue: adapted to contract
- connective tissue: adapted either to hold other tissue together / as a transport medium
Describe the epithelial tissue Squamous epithelium, it’s role and its structure.🌟
Structure:
- made of specialised, flattened squamous epithelial cells
- aka pavement epithelium due to flat appearance
- sits on a basement membrane
- v thin due to squat / flat cells that make it up, and also as is only one cell thick
Role:
- present when rapid diffusion across a surface = essential, as reduces dist of diffusion pathway
- forms lining of lungs + allows doe rapid diffusion of O2 into blood
Can be simple or stratified.
Simple = one layer of flattened squamous cells on basement membrane
Stratified = multiple layers of flattened squamous cells on basement membrane
Describe the epithelial tissue Ciliated Epithelium, it’s role and its structure.🌟
Structure:
- made of Ciliated epithelial cells, which have hair like structure called cilia on one surface that move in a rhythmic manner
- has goblet cells, releasing mucus to trap any unwanted particles present in air, preventing any bacteria reaching alveoli
Role:
- movement of cilia shifts material along surface of epithelium, making them specialised cells for their function
- Ciliated epithelium lines trachea for e.g. Causing mucus to be swept away from lungs
Describe the connective tissue Cartilage, it’s role, it’s location and its structure.🌟
Location: found in outer ear, nose + at ends of + between bones
Structure:
- contains fibre ps of protein elastin, to give flexibility, + collagen, to stiffen + strengthen it
- is firm + flexible
- composed of Chondrichthyes cells in the extracellular matrix
Role:
- prevents ends of bones rubbing together + causing damage
- provides strength + support
- resistant to tension + compression but not as strong as bone
Describe general muscle tissue.🌟
- needs to be able to shorten in length (contract) to move bones, which in turn move diff parts of body
- diff types of fibres: skeletal muscle fibres (muscles attached to bone, voluntary), smooth muscle (involuntary), + cardiac (only found in heart)
Describe the muscle tissue Skeletal muscle, it’s role and its structure.
Structure:
- contain myofibrils which contain contractile proteins
Role:
- highly specialised + are multinucleate
Aka muscle fibres (group of fibres = fascicle, group of fascicles = muscle)
Describe the muscle tissue Smooth muscle, its role, it’s location and its structure.
Location: trachea, bronchi, large bronchioles + other parts of body
Structure:
- contains elastic fibres
Role:
- elastic fibres give elasticity
Describe the specialised plant tissue The Epidermis, it’s role and its structure.
- a single layer of closely packed cells covering surface of plants
Structure:
- usually covered by waxy, waterproof cuticle to reduce loss of water
- has stomata that open and close - controlled by guard cells
Role:
- stomata in it allow CO2, O2 + water vapour in + out
Name the two main categories of tissue in plants and their adaptions to function.
- epidermis tissue: adapted to cover plant surfaces
- vascular tissue: adapted for transport of water + nutrients
Describe the organisation of tissues into organs.🌟
- organ = collection of tissues adapted to perform a particular function in an organism
E.g. Mammalian heart = organ adapted for pumping blood around body, made of muscle tissue + connective tissue.
Describe the organisation of organs into organ systems.🌟
- large multicellular organisms have coordinated organ systems, each composed of a no. of organs working together to carry out a major function in body Animal e.g's: - digestive system - cardiovascular system - gaseous exchange system
Describe stem cells and their division.🌟
- all cells begin undifferentiated, originating from mitosis / meiosis = called stem cells
- stem cells are able to undergo cell division repeatedly, + are source of new cells necessary for growth, development + tissue repair
- once stem cells become specialised, they lose ability to divide, entering G0 phase of cell cycle
- stem cell activity = strictly controlled, if do not divide fast enough, tissues are not efficiently replaced, leading to ageing
- but uncontrolled division leads to formation of masses of cells called tumours, which can lead to development of cancer
Describe stem cells’ ability to differentiate into different cell types.🌟
- this ability = its potency
- more no. of cell types it can differentiate into = greater potency
Describe what is meant by a Totipotent stem cell.🌟
- stem cells that can differentiate into any type of cell, as well as those destined to eventually produce a whole organism
- e.gs of totipotents: fertilised egg, zygote
Describe what is meant by a Pluripotent stem cell.🌟
- stem cells that can form all tissue types but not whole organisms
- present in early embryos + are origin of diff types of tissue within an organism
Describe what is meant by a Multipotent stem cell.🌟
- stem cells that can only form a range of cells in a certain type of tissue
- e.gs of multipotents: haematopoetic stem cells in bone marrow as this gives rise to various types of blood cells
Describe the production of erythrocytes derived from stem cells in bone marrow.🌟
- erythrocytes = red blood cells
- all blood cells derived from stem cells in bone marrow
- their lack of nucleus + organelles means only have a short lifespan (+/- 120 days) so need constant replacing
- so, stem cell colonies in bone marrow produce roughly 3 billion erythrocytes per kg of body mass per day
Describe the production of neutrophils derived from stem cells in bone marrow.🌟
- neutrophils = white blood cells
- all blood cells derived from stem cells in bone marrow
- neutrophils only love for roughly 6 hours + colonies of stem cells in bone marrow produce in region of 1.6 billion per kg per hour
- this amount produced also increases during infection
Describe some sources of animal stem cells.
- Embryonic stem cells: present at v early stage of embryo development + are Totipotent. After 7 days, a mass of cells (a blastocyst) forms + cells now pluripotent
- Tissue (adult) stem cells: present throughout life from birth, found in specific areas e.g. Bone marrow + are Multipotent. Can also be harvested from umbilical chords of newborns
Describe some sources of plant stem cells.
- present in Meristemic tissue (Meristems) in plants, this tissue found wherever growth is occurring in plants, e.g. at tips of roots + shoots (= apical meristems)
- Meristemic tissue also between phloem + xylem tissues (= vascular cambium)
- pluripotent nature of stem cells in meristems continues throughout life of plant
Describe the potential uses of stem cells in research and medicine.🌟
Stem cells transplanted into specific areas have potential to treat certain diseases e.g:
- heart disease
- type 1 diabetes
- Parkinson’s disease (treatment of neurological conditions)
- Alzheimer’s disease (“)
- birth defects
- spinal injuries
- macular degeneration
Stem cells are already used in diverse areas e.g:
- treatment of burns: can be grown to produce new skin (repair of damaged tissues)
- drug trials: can have new drugs tested on them before done on animals + humans
- developmental biology: important in this area (the study of changes tags occur as multicellular organisms grow + develop from a single cell) as they can divide indefinitely and differentiate into most cells of an organism (research)
Describe some of the ethics involved with using stem cells in medicine, specifically embryonic stem cells.
- removal of stem cells from embryos usually = destruction of of embryos, but techniques being developed to stop this damage
- religious + moral objections to use of embryos in this way (e.g. many believe destruction of embryo = murder, does embryo have rights? + who owns this genetic material?)
