Cell Division, Diversity and Differentiation Flashcards
Draw the cell cycle and label it
Interphase - G1 - S - G2 M phase - prophase - metaphase - anaphase - telophase Checkpoints - G1/S restriction checkpoint - G2/M - half way through M - early G1
What are the purpose of checkpoints and what do they ensure?
- prevent uncontrolled division that would lead to tumours
- detect and repair damaged DNA (UV)
- cycle cannot be reversed
- DNA is replicated only once in each cycle
Describe G0 phase
- resting phase triggered by early G1 at restriction point, by a chemical checkpoint
- cells undergo apoptosis, differentiation or senescence
- epithelial cells in gut don’t have this phase and neurons remain in this phase for a long time
Describe G1 phase
- G1 checkpoint control mechanism ensures that the cell is ready to enter S and begin DNA synthesis
- cells grow and increase in size
- transcription of genes to make RNA occurs
- organelles duplicate
- biosynthesis like protein synthesis and making enzymes needed for DNA replication - p53 tumour suppressor gene helps control this phase
Describe S phase
- specific sequence to the replication of genes (housekeeping genes which are active in all types of cells replicated first)
- it is committed when it enters
- DNA replicates
- each one has sister chromatids - rapid phase, exposed DNA base pairs are more susceptible to mutagenic agents (reduces chances of mutations)
Describe G2 phase
- special chemicals ensure that the cell is ready for mitosis by stimulating proteins that will be involved in making chromosomes condense and formation of spindle
- cells grow
Describe M phase
- checkpoint chemical triggers condensation of chromatin, half way through metaphase ChP ensures that cell is ready to complete mitosis
- cell growth stops
- prophase, metaphase, anaphase, telophase, cytokinesis
What is the significance of mitosis?
- asexual reproduction
- growth
- tissue repair
Describe prophase and include a drawing
- 2 identical sister chromatids now shorten and thicken
- nuclear envelope breaks down
- centriole divides and moves to opposite poles
- cytoskeleton threads form spindle between centrioles
Describe metaphase and include a drawing
- chromatids attach to the spindle threads at the equator region
- attach by their centromeres
Describe anaphase and include a drawing
- centromeres splits
- motor proteins walk along tubulin threads pull them in opposite directions to poles
- (v shape centromere go first)
Describe telophase and include a drawing
- reach poles
- new nuclear envelope forms
- contains two nuclei genetically identical
Describe cytokinesis
- splits in 2
- plasma membrane folds inwards and nips in the cytoplasm
- end plate forms where equator of spindle was new plasma membrane and cellulose wall either side of end plate
- 2 daughter cells genetically identical to each other and parent
What is the significance of meiosis?
- increases genetic variation which increases chance of survival when environment changes some will have characteristics
- makes haploid cells so when two gamete nuclei fuse fertilisation a diploid zygote is produced
What are homologous chromosomes?
23 maternal and 23 paternal chromosomes form matching pairs
Describe prophase 1
- chromatin condenses and chromosomes supercoils
- nuclear envelope breaks down and spindle threads form from centriole
- chromosomes go into homologous pairs (each pair = 2 chromatids)
- crossing over occurs non sister chromatids wrap around, swap sections
Describe metaphase 1
- pairs still crossed over attach to equator of spindle by centromere
- independent assortment
Describe anaphase 1
- members of each homologous chromosomes pulled apart by motor proteins drag along spindle threads
- centromeres don’t divide
- crossed over areas separate
Describe telophase 1
- two nuclear envelopes form around each set then divides by cytokinesis (interphase chromosomes uncoil) 2 chromatids
- plants anaphase 1 to prophase 2
Describe prophase 2
- nuclear envelope breaks down
- chromosomes coil and condense
- spindles form
Describe metaphase 2
- chromosomes attach to equator of spindle
2. chromatids randomly arranged
Describe anaphase 2
- centromeres divide
- chromatids of each chromosomes pulled apart by motor proteins drag opposite poles
- randomly segregated
Describe telophase 2
- nuclear envelope form around 4 haploid nuclei
- animals: 2 cells divide give 4 haploid cells
- plants: tetrad of 4 haploid
How meiosis produces genetic variation?
- crossing over in P1 shuffles alleles
- independent assortment in A1 random distribution of maternal and paternal chromosomes
- independent assortment of chromatids A2 random distribution material
- haploid undergo random fusion with gametes from another organism
Why is there a need for cell differentiation?
The process of becoming specialised
Muticellular organisms have smaller SA/V ratio so need specialised cells to carry out functions
Outline differentiation
Zygote is not specialised, it is a stem cell Embryonic cells become different by - proportions of different organelles - shape - some contents
Explain how erthrocytes are adapted to their function
- very small large SA:V O2 can diffuse across membrane easily
- biconcave shape increases SA:V
- flexible can travel through narrow capillaries
- no nucleus, mitochondria, ER + very little cytoplasm = more space for haemoglobin
Explain how neutrophils are adapted to their function
- 2X size of RBC
- contains multilobed nucleus
- attracted to and travel towards infection sites by chemotaxis
- ingest bacteria and some fungi by phagocytosis
Explain how spermatoza adapted to their function
- many mitochondria to carry out aerobic respiration ATP for tail to move
- small long and thin = move easily
- enzymes released from acrosome to get into the egg (digest)
- head contains haploid very little cytoplasm
How are palisade cells adapted to their function?
- long, cylindrical so pack together closely (some space for air between)
- large vacuole, chloroplasts are at top reduce diffusion distance
- chloroplasts = photosynthesis
- cytoskeleton + motor protein to move chloroplasts to upper (low sun)
Describe how guard cells work
- ATP actively transport K+ from epidermal into guard cells lowering WP
- water enters by osmosis from surrounding
- swell tips bulge (more flexible) stoma enlarges
- air enters, gaseous exchange CO2 O2 maintain a steep conc grad as used
- water and O2 diffuse out
Describe how root hair cells work
- projection increases SA for absorption water and nitrates
- mineral ions AT into root hair reduces WP causing water to follow by osmosis down a WP gradient
- carrier proteins to AP (ATP)
Describe epithelial tissue
- covers and lines body surfaces
- made entirely of cells
- form continuous sheets bound by lateral contacts e.g tight junctions and desosomes
- no blood vessels (tissue fluid underlying connective tissue)
- cilia, microvilli
- short cell cycles
- squamous flattened
- protection, absorption, filtration, excretion, secretion
Describe connective tissue
- non living extracellular matrix containibg collagen and elatin, polysaccarhides (hyaluronic acid traps H2O)
- separates living cells in tissue, enables it to withstand forces
- blood, bone, cartilage, tendons, ligaments
Define tissue
a group of cells that work together to perform a specific function
Describe cartilage
- immature chrondroblasts divide by mitosis and secrete extracellular matrix
- mature less active chrondrocytes maintain matrix
1. hyaline = embryonic skeleton, joins ribs, nose, trachea, larynx, covers ends of long bones
2. fibrous = discs between vertebrae in spine and knee joint
3. elastic = pinna and epiglottis
Describe muscle tissue and its functions
- well vascularised fibres elongated with myofilaments (actin and myosin) allow contraction
1. skeletal muscles joined to bones by tendons cause bones to move
2. cardiac muscle allows heart to pump
3. smooth muscle walls of intestine, blood vessels, uterus, urinary tract and propels substances along tracts
What are epidermal cells?
Flattened cells lack chloroplasts form protective layer over leaves, stems, roots. Some impregnated by wax = cuticle (reduces water loss)
Describe meristematic tissue
Contain stem cells, found root and shoot tips and in cambium
- have thin cell walls very little cellulose
- no chloroplasts
- no large vacuole
- divide mitosis and differentiate
Describe how xylem and phloem derive from meristems
Cambium cells become -
Xylem:
- lignin reinforce and waterproof but kills
- ends break down so xylem forms continuous columns
Pholem:
- sieve tubes lose most of organelles and sieve plates form between
- companion cells retain organelles provide ATP for active loading
List some plant organs
Leaf = photosynthesis Root = anchorage in soil, absorption of minerals water, storage Stem = support, holds leaves up so they're exposed to sun, transportation, storage of products of photosynthesis Flower = sexual reproduction
What is parenchyma, sclerenchyma and collenchyma?
P = packing tissue, fills spaces between other tissues can store starch C = thick cellulose walls, strengthen vascular bundles and outer parts of stem S = lignified walls strengthen stems and midribs
Define organ
a group of tissues working together to perform the same function
Define organ system
a number of organs working together to carry out an overall life function
Explain what organs and tissues with examples are involved in the digestive system and circulatory system
Digestive:
oesophagus, stomach, intestines, (glands), liver and pancreas
E.g nutrition to provide ATP and materials for growth and repair
Circulatory:
heart and blood vessels
E.g transport to and from cells
Explain what organs and tissues with examples are involved in the respiratory and urinary system
Respiratory:
airways, lungs, diaphragm, intercostal muscles
E.g breathing and gaseous exchange, excretion
Urinary:
kidneys, ureters, bladder
E.g excretion and osmoregulation
Explain what organs and tissues with examples are involved in integumentary and musculo-skeletal system
Integumentary: skin, hair and nails E.g waterproofing, protection, temperature regulation Musculo-skeletal: skeleton and skeletal muscles E.g support protection and movement
Explain what organs and tissues with examples are involved in the immune system and the nervous system
Immune system:
bone marrow, thymus gland, skin, stomach acid, blood
E.g protection against pathogens
Nervous system:
brain, spinal cord, nerves
E.g communication, control and coordination
Explain what organs and tissues with examples are involved in the endocrine system, reproductive and lymph system
Endocrine:
glands thyroid, ovaries, testes, adrenals
E.g communication, control and coordination
Reproductive:
testes, penis, ovaries, uterus, vagina
E.g reproduction
Lymph:
lymph nodes and vessels
E.g transports fluid back to circulatory and important in resisting infections
What are stem cells?
- undifferentiated cells
- pluripotent (totipotent can make all types AND placental)
- can express all their genes
- divide by mitosis
What are the sources of stem cells?
- embryonic stem cells (zygote begins to divide)
- umbilical cord blood
- adults blood, brain, muscle, bone, adipose, skin
- induced pluripotent cells iPS cells make differentiated cells into undifferentiated
Explain how stem cells can be used for bone marrow transplants and drug research
Treat diseases of the blood (sickle cell anaemia and leukaemia) and immune system (SCID)
Used to restore patients blood after treatment for cancer, SC obtained before, stored and put back in
New drugs can be tested first on these human tissues rather than animal tissues
Explain how stem cells can be used for developmental biology
- they study how these cells develop to make cell types and and learn how the cells function and see whats wrong when they are diseased
- try to see if they can extend the capacity that embryos have for growth, tissue repair into later life
Explain how stem cells can be used to repair damaged tissues or replace lost tissues
It is hard to culture stem cells in a lab
Find out what cytokine cell signalling molecules are needed to direct
1. treat mice with type 1 diabetes iPS cells into pancreatic beta cells
2. bone marrow = hepatocytes, treat liver disease
3. nerve tissue can treat Alzheimer’s, Parkinson’s or repair spinal cord
4. regenerative medicine populate bio-scaffold of an organ can develop and grow into organs, if using patients cells iPS no need for immunosurpressant drugs
5. could treat arthritis, strokes, burns, vision, hearing loss, muscular dis trophy, heart disease
What ethical issues are there with stem cells?
People reject using embryos because they are seen as potential humans fetus implanted into a uterus
Where can you find plant stem cells?
Meristem
Shoot tips
Cambium
What are the advantages of using embryonic stem cells instead of other types?
Pluripotent
More plentiful
easier to harvest
