B6 - cell division Flashcards
What are the two phases of the cell cycle?
- Interphase
- Mitotic phase
What are the stages of interphase?
G1:
- cell increases in size
- organelles synthesised
- proteins produced
- organelles replicate
S:
- DNA replication
G2:
- growth continues & produce proteins, energy stores increase & duplicated DNA checked for errors.
G0:
- STOPS, cell leaves cycle & doesn’t divide
- more cells leave the body as we age = senescent cells
- few cells that enter G0 can be stimulated to go back into cell cycle & start dividing again e.g. lymphocytes in an immune response.
What cells enter G0? (2)
Already differentiated: specialised for function, so no longer able to divide
Cells w/ damaged DNA: not viable/needed
What is the purpose of checkpoints in interphase?
- Ensures errors don’t occur e.g. an error in DNA replication could lead to a mutation
- monitor completion of phases before progresses to next phase, if errror, cell enters G0.
What are the different checkpoints in interphase and what do they check? (6)
G1 cp (cell begins DNA replication if it meets the requirements):
- cell size
-nutrients
- growth factors
- DNA damage
G2 cp (before start of the mitotic phase):
- cell size
- DNA replication
- DNA damage
metaphase cp (mitosis can’t proceed until this cp has passed):
- chromosomes & spindles attached & aligned
What is the purpose of interphase?
- Period of growth, preparing cell to divide
- cell still functions as normal
- cells mostly in interphase, otherwise would continuously divide
What are the 2 types of ways in which DNA can be stored? Explain their purpose.
Heterochromatin:
- Tightly wound & condensed DNA
- state of chromosomes in CELL DIVISION
- genes not transcribed
Euchromatin:
- loosely wound DNA
- state of chromosomes in INTERPHASE
- easily separated & genes can be transcribed.
What is chromatin?
DNA double helix wrapped around histones(proteins)
DNA + histones = chromatin
What are the 2 main stages of the mitotic phase?
- mitosis (nuclear division)
- cytokinesis ( cell membrane division)
What is mitosis and what is it used for?
- Parent cell divides into 2 genetically indentical daughter cells
- Exact same DNA copy & num of chromosomes
used for:
- replacement/repair of tissues
- asexual reproduction
- growth
Explain the stages of mitosis. (5)
PROPHASE:
- chromosomes condense, takes up stain & becomes visible under LM
- nucleolus disappears & nuclear membrane breaks down
- spindle fibres form & centrioles move to opposite poles of cell
- spindle fibres attach to centromeres & move chromosomes to centre
- nuclear envelope completely disappears
METAPHASE:
- Spindle fibres move chromosomes & align along metaphase plate in cell’s centre
- metaphase plate equator
ANAPHASE:
- centromeres divide
- spindle fibres shorten, pulling chromatid to opposite poles of cell (v shape)
TELOPHASE:
- chromatids reach pole of cell & become chromosomes
- nuclear envelope reforms around them
- chromosomes uncoil & nucleus reforms
- cleavage furrow: (cell-surface membrane pulled in by cytoskeleton)
CYTOKINESIS:
- contractile rings of microfilaments causes constriction, membrane divides into two cells.
What happens to the number of chromosomes before and after DNA replication?
- DNA replicated in interphase before mitosis
- 46 single chromosomes in somatic cell before replication
- 23 pairs of homologous chromosomes (1 maternal, 1 paternal) in body cell
- Replicated in S phase, replicate = sister chromatid
- 2 chromatids joined at centromere = 1 chromosome
What types of cells undergo mitosis and meiosis?
mitosis: somatic(body) cells
meiosis: cells in reproductive organs (testes & ovaries)
Why don’t plant cells have a cleavage furrow? And how do plant cells divide?
- Have cell wall
- cleavage furrow not possible/ NO CYTOKINESIS
- vesicles assemble at metaphase plate & fuse together, new cell wall synthesised from vesicles
- cell splits into 2.
What happens during sexual reproduction?
- 2 gametes (1 from each parent) fuse & produce a zygote (fertilised egg - origin of all cells in an organism)
- Contains 1/2 diploid num otherwise chromosomes would double after every round of reproduction.
What is the purpose of meiosis?
- occurs in diploid cells in the reproductive organs & forms haploid gametes for sexual reproduction.
Describe the process of meiosis I. (5)
PROPHASE I:
- same as mitosis BUT homologous chromosomes pair up & form bivalents.
- Crossing over occurs (chromatids entangle)
METAPHASE I:
- same as mitosis BUT homologous pairs assemble along metaphase plate
- Independent assortment (diff/random orientation of homologous pairs means that maternal or paternal could face diff poles of cell) = more genetic variation when cell divides
ANAPHASE I:
- Homologous chromosomes split & pulled to opposite poles of cell
- chromatids stay joined together
- sections of sis chromatids (entangled from crossing over) break and rejoin at the chiasmata = exchange DNA = form recombinant chromatids
- Sis chromatids no longer identical as different allele combination.
TELOPHASE:
- same is mitosis I
CYTOKINESIS:
Diploid cell becomes haploid
Describe the process of meiosis II.
PROPHASE II:
- chromosomes condense, nuclear envelope breaks, spindle fibres form
METAPHASE II:
- individual chromosomes line along metaphase plate
- Independent assortment of chromatids not identical due to crossing over = even more genetic variation
ANAPHASE II:
-same as mitosis (chromosomes pulled)
TELOPHASE II:
- Chromosomes uncoil and form chromatin
- Nuclear envelope reforms
- nucleolus visible
CYTOKINESIS:
- 4 non-identical daughter cells.
- haploid due to reduction division.
In which 3 ways does genetic variation occur?
1) Independent assortment of homologous chromosomes in metaphase I
2) Crossing over
3) Independent assortment of chromatids in metaphase II
How does crossing over occur?
SYNAPSIS = homologous chromosomes join to form bivalents
-chromatids break & recombine
- 4 diff chromatids
- diff order of genes = introduces genetic variation
What are the properties of squamous epithelium?
- 1 cell thick, flat, v smoot= rapid diffusion of O2 into blood
- lining of blood vessels, alveoli, atria, ventricles
What are the properties of ciliated epithelium?
- hair-like cilia
- lines trachea & sweeps mucous away from lungs
- goblet cells release mucous to trap unwanted particles in the air & prevent bacteria etc. reaching alveoli in lungs.
What are the three muscle tissues in animals?
Skeletal: attached to bone (have microfibrils w/ contractile proteins)
Cardiac: Heart
Smooth: wall of small intestine & arterioles etc.
-contract slowly and powerfully for long periods e.g. peristalsis.
What is cartilage? (3)
- Specialised tissue
- connective tissue between bones
- contain elastin & collagen fibres
- made of chondrocyte cells embedded in extracellular matrix
- prevent bones rubbing against each other.
What cells make up cartilage?
chondrocyte cells
Name some connective tissues in animals.
- loose (e.g. adipose)
- dense (e.g. tendons, ligaments)
- cartilage
- bone
- blood
- lymph (transport medium)
What is the general role of epithelial cells?
cover surface & form lining (1 cell thick & rest on collagen proteins)
What is the role of the cardiovascular system? Name some organs in this organ system. (2)
- Pump blood around body & provide transport system
Organs:
heart, lungs, blood vessels
What is the role of the digestive system? Name some organs in this organ system. (4)
- Breaks down large insoluble molecules into smaller, soluble ones to be absorbed into blood
- Retains water needed by body & removes undigested material
-Bile emulsifies fat & neutralises acid going to the small intestine
Organs:
oesophagus, stomach, small intestine, large intestine, bladder, pancreas
What is the role of the gaseous exchange system? Name some organs in this organ system.
- Extract O2 for respiration & expel CO2 from body.
Organs:
lungs, larynx, trachea, alveoli
Sperm cells are specialised animal cells. How are they specialised for their role?
- male gametes that deliver genetic info to the female gamete (egg)
- acrosome has digestive enzymes which digest protective ovum layer, so can penetrate
- flagellum for movement & mitochondria provides energy to swim.
Sperm cells are specialised animal cells. How are they specialised for their role? (3)
- male gametes that deliver genetic info to the female gamete (egg)
- acrosome has digestive enzymes which digest protective ovum layer, so can penetrate
- flagellum for movement & mitochondria provides energy to swim.
How are erythrocytes specialised for their role? (3)
- biconcave/flattened shape increases SA:V to transport O2 around body
- No nucleus = more space for haemoglobin to carry O2.
- flexible so can squeeze through capillaries.
How are neutrophils specialised for their role? (2)
- multi-lobed nucleus = fit through small gaps to get to infection sites.
- Granular cytoplasm w/ many lysosomes containing enzymes to digest pathogens
Define a tissue
- group of specialised cells
- each tissue adapted to a particular function
Define an organ
collection of tissues adapted to perform a particular function in an organism e.g. leaf = organism adapted for photosynthesis
Define an organ system
- organs working together to carry out major functions in the body
What specialised tissue covers a plant’s surface?
epidermis
- single layer of closely packed cells
- covered by waxy cuticle(waterproof to reduce water loss)
What are the two vascular systems in plants adapted for transport? Briefly explain then in detail. (4)
Xylem:
- transport water & minerals from roots to leaves
- walls strengthened w/ lignin (waterproof structural support)
- DEAD cells
Phloem:
- transport organic nutrients & sugars from leaves & stems (made by photosynthesis) to anywhere needed
- companion cells provide energy for sieve plates, which have pores in the end walls
- Have cytoplasm but no nucleus or ribosomes (more room to transport substances)
How are palisade cells (present in mesophyll) specialised for their function?
- large vacuole to maintain turgor pressure, otherwise would fold = hard for chloroplasts to absorb light for photosynthesis.
- Cells packed into box shape to form a continuous layer
- Thin cell wall = more diffusion of CO2
- chloroplasts move in cytoplasm = absorb more.
How are guard cells specialised for their function?
- thicker inner cellulose cell wall is less flexible, so guard cells bend around creating an opening
- CO2 can enter plants for photosynthesis
- lose water = change shape & stomata closes to prevent further water loss.
How do guard cells create an opening in the stomata?
- Actively pump K+ into vacuole
- lowers water potential
- water enters by osmosis
- guard cells swell with water
- thicker cell wall causes guard cells to curve open, creating a gap in the stomata
How are root hair cells specialised for their function?
- In root surfaces or tips
- Long root hair extensions increases surface area to maximise uptake of water & minerals from the soil
Magnesium and nitrates are taken up into root hair cells. What are they for?
magnesium: make chlorophyll
nitrates: make amino acids
What are the different 3 types of stem cells? (in detail) (6)
Totipotent:
- Can differentiate into any type of cell, including extraembryonic cells such an the umbilical cord & placenta.
- Only totipotent for up to 8-cell stage
Pluripotent:
- Can form all tissues except extraembryonic tissues (placenta & umbilical cord)
- can’t form whole organism
- found in inner cell mass of blastocyst
Multipotent:
- Form a range of cells within certain types of tissue.
- No toti or pluri potent cells in a fully formed mammal, which is why we can’t regenerate body parts.
- Adult stem cells in specific tissues = multipotent
- e.g. haematopoietic stem cell in bone marrow differentiates into various types of blood cells.
What are stem cells?
- undifferentiated cells originated from mitosis or meiosis.
- not adapted to a particular function BUT have potential to form any specialised cell = totipotent.
e.g. a zygote divides into a whole organism as the embryo grows.
How can one stem cell form multiple specialised cells?
- Can self-renew & undergo division/mitosis indefinitely to differentiate into many different cells.
What are the two types of self-renewal in stem cells?
symmetric: divides into 2 stem cells
asymmetric: divides into 1 stem cell & 1 non-stem cell
What does differentiation mean?
- cell becoming specialised for a specific function
- must be adapted to role e.g. unique shape & specific organelles.
What is the plant source of stem cells/human totipotent cells equivalent?
- found in actively growing areas in plants called MERISTEM
MERISTEM in tips of roots & shoots & in cambium (between xylem & phloem)
What are the sources of stem cells in animals?
Embryonic stem cells:
- early stages of embryo development
- totipotent
Adult stem cells:
- found in tissues such as bone marrow
multipotent
- also found in umbilical cord = plentiful supply
- can be stored
What is a blastocyst?
- Cluster of dividing cells
- inner cell mass of a blastocyst has pluripotent stem cells
- trophoblast sticks to wall of uterus, forming the placenta & umbilical cord.
Name 3 ways in which stem cells can be used. (3)
Treating burns:
- stem cells grow on biodegradable meshes
- can produce new skin (quicker than removing from another body part)
Drug trials:
- tested on stem cells before humans & animals
Transplants:
- potential to treat diseases e.g. heart disease, alzheimers (dementia = brain cells destroyed), parkinson’s (brain)
What are the ethical concerns surrounding stem cells from embryos?
- removing stem cells from embryos often destroys them
- destroying a potential life = murder?
- This controversy holds back progress of treating diseases.
What are iPSCs? And why are they so important? (4)
Induced pluripotent stem cells
- modify adult stem cells to act as pluripotent stem cells
Why?
- many unsuccessful organ transplants due to rejection
- turn adult stem cell into iPSC & into a specific new organ.
- eliminates rejection concern & removes ethical objections of IVF embryos as doesn’t involve the loss of an embryo.
How can umbilical cord stem cells be used in medicine?
- haematopoietic cells in blood from umbilical cord
- differentiate into blood cells, bone, cartilage
- used in regenerative medicine, later in the same person’s life
- own cells = less rejection risk
How can adult stem cells be used in medicine? (3)
Bone marrow transplants (haematopoietic stem cells found in bone marrow)
1) Healthy bone marrow from donor stored in freezer
2) recipient treated with high-dose chemotherapy to destroy their own bone marrow.
3) frozen healthy bone marrow transfused into recipient to replace destroyed bone marrow & produce blood cell types normally.
Where are haematopoietic stem cells and where are they found?
- Adult stem cells found in bone marrow
- multipotent
- differentiate into blood cell types
