Chap 6 - Cell Division Flashcards
List the stages of the cell cycle in order and outline what happens at each stage.
- interphase –> period of normal functioning, growth and DNA replication
- mitotic phase (nucleus and cytoplasm divide) –> mitosis and cytokinesies - period of cell division
List 3 stages of interphase in order and describe what happens at each stage.
- G1 - proteins from which organelles are synthesised are produced, organelles replicate and cell increases in size
- S - synthesis phase - DNA is replicated in the nucleus
- G2 - cell continues to increase in size, energy stores increased, duplicated DNA checked for errors
List 2 stages of mitotic phase, outline what happens at each stage.
- mitosis - nucleus divides
- cytokinesis - cytoplasm divides and two cells are produced
What 3 reasons might a cell enter G0
- damaged DNA - damaged cells cannot divide
- differentiation - specialised cells that carry out specific function cannot divide
- as you age, cells need to be regulated
Define the G0 stage
the phase when cell leaves the cell cycle temporarily or permanently
Outline the role of checkpoints to control the cell cycle.
- ensures that a cell only divides when it has grown to the right size
- ensures that the replicated DNA is error free
- ensures that chromosomes are in correct positions during mitosis
Give 3 examples of cell cycle checkpoints.
- G1 checkpoint
- G2 checkpoint
- M checkpoint (spindle assembly checkpoint)
State where G1 checkpoint occurs, what is checked at the checkpoint and what happens if cell passes/fails.
- checks: cell size, nutrients, growth factors, DNA dmg
- if requirements satisfied - DNA replication begins
- if requirements not satisfied - cell enters G0
State where G2 checkpoint occurs, what is checked at the checkpoint and what happens if cell passes/fails.
- checks: cell size, DNA replication, DNA damage
- if requirements satisfied - molecular processes that signal beginning of mitosis initiated
- if requiremetns not satisfied - cell pauses at G2 to try and repair, if irreparable cell undergoes apoptosis
State what is checked at M checkpoint, and what happens if cell passes/fails.
- checks if all chromatids are correctly attached to spindle fibers
- if requirements satisfied - cell continues with mitosis
- if requirements not satisfied - mitosis paused, repair attempted
Define mitosis
nuclear division stage in mitotic phase of the cell cycle
Define chromosome
- structure of condensed and coiled DNA in the form of chromatin
- become visible under light microscope when preparing to divide
Define chromatids
one of two halves of a replicated chromosome
Define sister chromatids
identical copies formed by DNA replication of a chromosome with both copies joined together by a common centromere
Define centromere
region at which two chromatids are held together
Define spindle fibres
structures made of microtubules that organise chromosomes and pull them apart to opposite poles during mitosis
Define homologous pairs
matching pair of chromosomes, one inherited from each parent
Describe how DNA is packaged in a chromosome
- DNA is wound around proteins (histones) making it more compact - chromatin
- During interphase, chromatin is decondensed
- During mitosis - chromatin is condensed - chromosomes
List the stages of mitosis in order
- prophase
- metaphase
- anaphase
- telophase
Describe what occurs during prophase.
- chromatin fibers begin to coil & condense forming chromosomes (visible if stained)
- nucleolus disappears, nuclear membrane starts breaking down
- protein microtubules form spindle fibers
- if cell has centrioles, they migrate to opposite poles of cells
- spindle fibers attach to specific areas on centromeres, start moving chromosomes to center
- by the end, nuclear envelope has disappeared
Describe what occurs during metaphase
chromosomes are moved by spindle fibers and line up along the equator of the cell
Describe what occurs during anaphase
- centromeres holding pairs of chromatids in each chromosome divide
- chromatids separated - pulled to opposite ends by shortening of spindle fibers
Describe what occurs during telophase
- the two new sets of chromosomes asemble at each pole
- nuclear envelope reforms around chromosomes
- chromosomes start to uncoil, nucleolus is formed
- cytokinesis begins
Explain the role of centrioles and spindle fibers in mitosis.
- centrioles organise spindle fibers which are attached to them
- spindle fibers pull chromatids to opposite poles and ensure even chromosome distribution between daughter cells
Describe the process of cytokinesis in animal cells.
- cleavage furrow forms around middle of the cell
- plasma membrane pulled inwards by cytoskeleton until close enough to fuse around middle
- two cells are formed as a result
Describe the process of cytokinesis in plant cells.
- vesicles from Golgi assemble along equator (metaphase plate)
- vesicles fuse with each other and cell surface membrane, dividing the cell into two
- new sections of cell wall form along new sections of membrane
- (cleavage furrow cannot form because plant cells have cell walls)
Compare animal and plant cytokinesis.
- animal cells: cleavage furrow, plant cells do not because of cell wall and high internal pressure
- plant cells: vesicles for cytokinesis
Describe the purpose of mitotic cell division.
- ensures that both daughter cells produced when a parent cell divides are genetically identical
- necessary when all of the daughter cells have to be identical
List 4 roles of mitosis.
- growth of organisms
- repair/Replacement of tissues
- embryo development
- asexual reproduction (production of genetically identical offspring from one parent in multicellular organisms)
Define diploid
two complete sets of chromosomes, one from each parent
Define haploid
containing one chromosome from each homologous pair
Define gamete
haploid sex cell produced by meiosis in organisms that reproduce sexually
Define zygote
- initial diploid cell formed when two gametes are joined by sexual reproduction
- earliest stage of embryonic development
Define meiosis
- nuclear division for the purpose of gamete production
- nucleus divides twice resulting in forming four haploid cells from one diploid cell
Define meiosis
- nuclear division for the purpose of gamete production
- nucleus divides twice resulting in forming four haploid cells from one diploid cell
Define reduction division
where the chromosome number is halved from diploid to haploid (first meiotic division)
Explain the role of meiosis in life cycles.
- production of gametes which allows sexual reproduction
- ensures all organisms produced via sexual reproduction contain correct # of chromosomes - if this didn’t occur: # of chromosomes would double with every round of reproduction
- produces genetic variation
State the ways in which meiosis produces variation.
- crossing over during prophase 1
- independent assortment of chromosomes in metaphase 1
- independent assortment of chromatids in metaphase 2
Suggest the importance of the creation of different allele combinations in populations.
- different phenotypes will be produced
- reduces the chances of a population going extinct - more likely that some individuals posess advantageous characteristics to help them survive and adapt
Define homologous chromosomes.
matching pair of chromosomes, one inherited from each parent
Define bivalent
a pair of homologous chromosomes during (crossing over)
Define crossing over
exchange of genes between homologous chromosomes, resulting in a mixture of parental characteristics in offspring
Define chiasmata
points at which chromatids break and rejoin
Define recombination
- process where pieces of DNA are broken and recombined to produce new combinations of alleles
- formed by crossing over of chiasmata in meiosis
State the stages of meiosis in order
- prophase 1
- metaphase 1
- anaphase 1
- telophase 1
- prophase 2
- metaphase 2
- anaphase 2
- telophase 2
What happens at P1?
- chromosomes condense, nuclear envelope disintegrates, nucleolus disappears
- spindle formation begins
- homologous chromosomes pair up, forming bivalents & crossing over occurs
What happens at M1?
- homologous pairs assemble along metaphase plate
- independent assortment occurs
What happens at A1?
- homologous chromosomes pulled to opposite poles and chromatids stay joined to each other
- entangled sections of DNA on non-sister chromatids break off and rejoin at chiasmata, resulting in formation of recombinant chromatids
What happens at T1?
- chromosomes assemble at each pole, nuclear membrane reforms
- chromosomes uncoil
- cytokinesis occurs, cell divides into two
- reduction of chromosome number from diploid to haploid is complete
What happens at P2?
- chromosomes that still consist of two chromatids condense and become visible
- nuclear envelope breaks down, spindle formation begins
What happens at M2?
- individual chromosomes assemble on metaphase plate
- due to crossing over, chromatids are not identical - independent assortment occurs
What happens at A2?
chromatids of individual chromosomes are pulled to opposite poles after division of centromeres
What happens at T2?
- chromatids assemble at poles, uncoil and form chromatin
- nuclear envelope reforms, nucleolus is visible again
- cytokinesis results in division of the cells forming four daughter cells in total
- daughter cells will be haploid and genetically different from each other & from parent cell
Describe the process of crossing over and explain how it produces genetic variation.
- homologous chromosomes pair up, forming a bivalent
- non-sister chromatids become entangled at points called chiasmata
- they break off and re-join, sometimes resulting in an exchange of DNA forming recombinant chromatids with different combinations of alleles and therefore genetic variation
Describe the process of random independent assortment and explain how it produces genetic variation.
- orientation of each homologous pair on metaphase plate is random and independent of any other homologous pair
- maternal or paternal chromosomes can end up facing either pole
- this means that the daughter cells can end up with any combination of maternal and paternal chromosomes hence why it produces genetic variation
Outline the levels of organisation of a multicellular organism in order.
specialised cells - tissues - organs - organ systems - whole organisms
Define specialised.
having particular structure to serve a specific function
Define differentiated
specialised to carry out very specific functions
Define cell
the smallest structural and functional unit of an organism
Define tissue
a collection of cells, of one or more types, working together to perform a function
Define organ
a collection of different tissues working together to perform a function
Define organ system
a collection of organs working together to perform a function
Explain why multicellular organisms have specialised cells.
- multicellular organisms are complex and require different organ systems to function
- specialised cells carry out their functions very efficiently
Describe how erythrocytes are specialised for their function.
- flattened biconcave shape - increases SV ratio
- flexible - able to squeeze through narrow capillaries
- no nuclei & many other organelles in mammals - more space for haemoglobin that carries oxygen
- these features are all essential for their role of transporting oxygen around the body
Describe how neutrophils are specialised for their function.
- multi-lobed nucleus to squeeze through small gaps to get to the site of infection
- granular cytoplasm contains many lysosomes to contain enzymes used to attack pathogens
- these features allow neutrophils to combat infections as part of the immune system
Describe how sperm cells are specialised for their function.
- tail/flagellum - capable of movement
- many mitochondria - energy supply for swimming
- acrosome - contains digestive enzymes to allow sperm to penetrate the ovum and fertilise
- these features all allow the sperm cell to deliver genetic information to the female gamete
Describe how palisade cells are specialised for their function.
- chloroplasts - absorb large amounts of light for photosynthesis
- rectangular box shape - closely packed to form continuous layer
- thin cell walls - increased rate of diffusion of CO2
- large vacuole - maintain turgor pressure
- chloroplasts able to move within cytoplasm to absorb more light
- these features allow the cells to maximise the rate of photosynthesis of the plant
Describe how root hair cells are specialised for their function.
- long extensions (root hairs) - increase surface area of cell
- this feature maximises the uptake of water and minerals from the soil - its function
Describe how guard cells are specialised for their function.
- they form small openings on surfaces of leaves - stomata
- stomata allow CO2 to enter plants but also allow water to exit plants
- when the cells lose water, they become less swollen due to osmotic forces, change shape and stoma closes to prevent further water loss from plant
- cell wall is thicker on one side so the cell does not change shape symmetrically as volume changes
State the 4 main categories of tissues in animals.
- nervous tissue - support transmission of el. impulses
- epithelial tissue - cover body surfaces, internal and external
- muscle tissue adapted to contract
- connective tissue - adapted to hold tissues together/as a transport medium
Describe how squamous epithelium is specialised for its function.
- made up of specialised squamous epithelial cells
- very thin bc it is one cell thick & the cells are flat - small diffusion distance
- its present when rapid diff. across a surface is essential (lining of lungs)
Describe how ciliated epithelium is specialised for its function.
- made up of ciliated epithelial cells & goblet cells
- cilia (hair-like structures) - move in rythmic manner, causing mucus to be swept away from the lungs
- goblet cells - release mucus to trap unwanted particles from the air
- the function of the tissue is to prevent particles & pathogens from reaching the alveoli once inside lungs
- found in the trachea
Describe how ciliated epithelium is specialised for its function.
- made up of ciliated epithelial cells & goblet cells
- cilia (hair-like structures) - move in rythmic manner, causing mucus to be swept away from the lungs
- goblet cells - release mucus to trap unwanted particles from the air
- the function of the tissue is to prevent particles & pathogens from reaching the alveoli once inside lungs
- found in the trachea
Describe how cartilage is specialised for its function.
- firm, flexible connective tissue composed of chondrocyte cells embedded in extracellular matrix containing elastin & collagen
- this helps prevent ends of bones from rubbing together & causing damage
- found in outer ear, nose, ends of & between bones
Describe how muscle tissue is specialised for its function.
skeletal muscle fibres contain myofibrils that contain contractile proteins - allow muscle tissue to contract in order to move bones - moves diff parts of the body
Describe how epidermis tissue is specialised for its function.
- single layer of closely packed cells that covers surface of plants
- covered by waxy waterproof cuticle - reduces loss of water
- stomata (formed by guard cells) - allow CO2, H2O and O in and out
Describe how xylem tissue is specialised for its function.
- vascular tissue responsible for transport of water and minerals throughout plants
- vessel elements (elongated dead cells) walls of them strengthened with lignin - structural supoport for plants
Describe how phloem tissue is specialised for its function.
- vascular tissue in plants responsible for transport of organic nutrients (sucrose) from leaves and stems where it is made to other parts of the plant
- composed of columns of sieve tube cells separated by perforated walls (sieve plates)
State 3 examples of organ systems in animals and for each describe their funciton.
- digestive system - takes in food, breaks down large insoluble molecules into small soluble ones, absorbs nutrients into the blood, retains water needed by body and removes undigested material from body
- cardiovascular system - moves blood around the body to provide a transport system for the substance it carries
- gaseous exchange system - brings are into the body so O can be extracted for respiration and CO2 can be expelled
Define stem cell
undifferenciated cell with the potential to differentiate into a variety of the specialised cell types of the organism
Define undifferentiated
unspecialised cell originating from mitosis or meiosis
Define totipotent
stem cells capable of dividing to produce all the cell types to form a whole organism
Define pluripotent
stem cells capable of dividing to produce all cell types but not the extra-embryonic membranes so not a whole organism
Define multipotent
- stem cells capable of dividing to produce several cell types
- adult stem cells are an example
Define embryonic stem cell
also known as pluripotent stem cells
Define tissue (adult) stem cells.
also known as multipotent stem cells
Describe the characteristic abilities of stem cells compared to specialised cells.
- stem cells are able to undergo cell division again and again indefinitely, specialised cells are not able to undergo cell division at all
- they are able to differentiate into other cell types, specialised cells are not
Explain the importance of stem cells and why their activity must be carefully controlled.
- they are the source of new cells for growth, development and tissue repair
- if they dont divide fast enough - tissues not efficiently replaced - ageing
- if they too quickly without control - tumors which could lead to cancer
State the 3 types of stem cell and give examples of where they occur in animals.
- totipotent - zygote and the 8/16 cells from its first few mitotic divisions
- pluripotent (embryonic stem cells) - early embryos
- multipotent (adult stem cells) - bone marrow
State where stem cells occur in plants and state which potency they have.
- found in meristematic tissue (meristems) - wherever growth is occurring in plants
- this tissue also found between xylem and phloem - vascular cambium
- they’re pluripotent
Outline how a cell becomes specialised.
- stem cells in the cell cycle replicate indefinitely until
- at one point, specific genes within a stem cell activate, causing it to differentiate by expressing features required for its function and become specialised
- this cell has entered G0 once specialised and cannot divide anymore
Explain why it is important for erythrocytes and neutrophils to be constantly produced.
- erythrocytes are essential for transport of oxygen around the body, since they have no nucleus - short lifespan (120 days) so they need to be replaced constantly
- neutrophils have an important role in immune system and only live about 6 hours so they must constantly be replaced (even more produced when infected)
Outline how xylem vessels and phloem sieve tubes are produced from meristems.
- meristematic tissue located between xylem and phloem tissues - vascular cambium
- cells originating from this region differentiate into diff cells present in xylem and phloem tissues
List 7 diseases that stem cells have the potential to treat.
- heart disease
- type 1 diabetes
- parkinson’s disease
- alzheimer’s disease
- macular degeneration
- birth defects
- spinal injuries
Suggest how stem cells could be used to treat heart disease.
can use stem cells to repair damage in muscle tissue in heart caused by heart attack
Suggest how stem cells could be used to treat type 1 diabetes.
stem cells could replace insulin-producing cells in the pancreas that were destroyed by the body’s own immune system
Suggest how stem cells could be used to treat parkinson’s disease.
stem cells could replace dead dopamine-producing cells in the brain
Suggest how stem cells could be used to treat Alzheimer’s disease.
replacing brain cells destroyed due to buildup of abnormal proteins
Suggest how stem cells could be used to treat macular degeneration.
replacing cells in the retina to prevent blindness in elderly and diabetics
Suggest how stem cells could be used to treat spinal injuries.
replacing damaged spinal cords using stem cell implants
Describe how stem cells may be useful for treating burns.
- stem cells grown on biodegradable meshes can produce new skin for burn patients
- quicker than taking graft from another part of body
Describe two ways in which stem cells may be useful in research.
- drug trials - new drugs can be tested on cultures of stem cells before being tested on animals and humans
- developmental biology - can divide indefinitely and differentiate into various types of cells they can be used to study changes that occur as multicellular organisms grow and develop from a single cell and why things go wrong
Describe arguments for the use of embryonic stem cells for research and medicine.
- allow us to find treatments for incurable diseases
- allow us to study developmental biology more closely
- embryoes used were donated from those left over after fertility treatment so they were gna be discarded anyway
Define the term induced pluripotent stem cell
adult stem cells that have been genetically modified to act like embryonic stem cells and so they are plurpotent
Explain why induced pluripotent stem cells may be very useful in research and medicine.
this could be useful as a replacement for actually harvesting embryonic stem cells as it is not as controversial
