Cell division, diversity and differentiation Flashcards
(85 cards)
1
Q
How do eukaryotic cells reproduce
A
Duplicate their contents, split into 2 daughter cells
2
Q
How has knowledge about the cell cycle changed over time, why
A
Early researchers- could only see the behaviour of chromosomes during mitosis and cytokineses
Discovered interphase between each M phase- not much can be seen under microscopes- need sophisticated techniques to see elaborate preparations
3
Q
word for cell death
A
apoptosis
4
Q
What helps to regulate the eukaryotic cell cycle
A
checkpoints
5
Q
What are the main checkpoints in the eukaryotic cell cycle
A
G1/S (restriction point)
G2/M
Others- e.g. halfway through M, early G1
6
Q
Purpose of checkpoints
A
- Prevent uncontrolled cell division that would lead to tumours (cancer)
- To detect and repair damage to DNA (e.g. damage caused by UV light)
Because the molecular events that control the cell cycle happen in a specific sequence, they also ensure that:
- the cycle can’t be reversed
- the DNA is only replicated once during each cell cycle
7
Q
Phases of the cell cycle
A
Interphase- G1/G0, S, G2
M
8
Q
G0
A
Gap 0 phase:
- resing phase triggered in early G1 at the restriction point by a checkpoint chemical
- some cells e.g. epithelial cells lining the gut don’t have this
Events:
- cells may undergo apoptosis (programmed cell death), differentiation, or senescence
- some types of cells e.g. neurones may remain in this phase for a very long time, or indefinitely
9
Q
G1
A
Gap 1 phase- aka growth phase:
- A G1 checkpoint control mechanism ensures the cell is ready to enter S phase and begin DNA synthesis
Events:
- Cells grow and increase in size
- transcription of genes to make RNA occurs
- organelles duplicate
- Biosynthesis e.g. protein synthesis, including enzymes needed for DNA replication in S phase
- The p53 (tumour suppressor) gene helps control this phase
10
Q
S
A
synthesis phase of interphase:
- because the chromosomes are unwound and the DNA is diffuse, every module of DNA is replicated
- There is a specific sequence to the replication of genes: housekeeping genes (those which are active in all types of cells) are replicated first, genes that are normally inactive in specific types of cells are replicated last
Events:
- once the cell has entered this phase, it is committed to completing the cell cycle
- DNA replicates
- when all chromosomes have been duplicated, each one consists o a pair of identical sister chromatids
- this phase is rapid- and because the exposed DNA base pairs are more suspectable to mutagenic agents, this reduces the chances of spontaneous mutations happening
11
Q
G2
A
Gap 2 phase of interphase:
- special chemicals ensure that the cell is ready for mitosis by stimulating proteins that will be involved in making chromosomes condense and in the formation of the spindle
Events:
- cells grow
12
Q
M
A
- a checkpoint chemical triggers the condensation of chromatin
- halfway through the cycle, the metaphase checkpoint ensures that the cell is ready to complete mitosis
Events:
- cell growth stops
- nuclear division (mitosis0
- cytokinesis (cytoplasmic division)
13
Q
The importance of mitosis
A
Asexual reproduction:
- single-celled protoctists such as amoeba and paramecium divide by mitosis to produce new individuals
- some plants e.g. strawberry, reproduce asexually by forming new plants on the end of stolons (runners)
- fungi e.g. single-cell yeasts can reproduce asexually by mitosis
- asexual reproduction n is rarer in animals but some female sharks kept in captivity without any males have produced female offspring that are genetically identical to themselves
- aphids may sometimes produce eggs, by mitosis, that don’t need fertilising
Growth:
- all multicellular organisms grow by producing new cells that are genetically identical to each other and to the parent cell from which they arose by mitosis
Tissue repair:
- wounds heal when growth factors, secreted by platelets and macrophages (white blood cells) and damaged cells of the blood-vessekl walls, stimulate the proliferation of endothelial and smooth muscle cells to repair damaged blood vessels
14
Q
4 phases of mitosis
A
Prophase
Metaphase
Anaphase
Telophase
15
Q
Mitosis- prophase
A
- chromosomes that have replicated during S phase of interphase and consist of 2 identical sister chromatids now thicken and shorten as DNA supercoils
- nuclear envelope breaks down
- the centriole in animal cells (normally found within a region called a centrosome) divides and the 2 new daughter centrioles move to opposite poles of the cell
- cytoskeleton protein (tubulin) threads form a spindle between these centrioles. The spindle has a 3D structure (like lonitude lines on globe), formed from part of cytoplasm
16
Q
Mitosis- metaphase
A
- the pairs of chromatids attach to the spindle threads at the equator region
- they attach by their centromeres
17
Q
Mitosis- anaphase
A
- the centromere of each pair of chromatids splits
- motor proteins, walking along the tubulin threads, pull each sister chromatid of a pair, in opposite directions, towards opposite poles
- because the centromere goes first, the chromatids (now called chromosones) assume a V shape
18
Q
Mitosis- telophase
A
- the separated chromosomes reach teh poles
- a new nuclear envelope forms around each set of chromosomes
- the cell no contains 2 new nuclei, each genetically identical to each other and to the parent cell from which they arose
19
Q
Process by which the cell splits, describe it
A
Cytokinesis:
- in animal cells, the plasma membrane folds inwards and ‘nips in’ the cytoplasm
- in plant cells, an end plate formed where the equator of the spindle was, and new plasma membrane and cell-wall material are laid down on either side along this endolate
- 2 new daughter cells are now formed- they are genetically identical to each other and to the parent cell
20
Q
Significance of meiosis in life cycles
A
- produces genetic variation
- increases chance of survival of population when environment changes as some individuals will have characteristics that allow them to be better adapted to the change
- sexual reproduction
21
Q
What does meiosis produce, how they are used
A
- 4 haploid gametes
- when 2 gamete nuclei fuse during fertilisation, a diploid zygote is produced
- ‘meiosis’ means reduction
22
Q
Describe the starting of meiosis
A
- Occurs in diploid germ cell (primary spermatocyte/ oocyte) to produce haploid gametes
- Diploid cells undergoing meiosis are in special organs called gonads- ovaries and testes
- these cells have been in interphase before they enter meiosis
23
Q
Describe homologous chromosomes
A
- in your body cells theer are 46 chromosonrs
- 23 from mother in egg nucleus, 23 from father in sperm nucleus
- can form matching pairs- one maternal and one paternal chromosome
- containing the same alleles genes at the same places
- may have different alleles of the same genes
- similar size
24
Q
Name meiosis phases
A
- Before, during S of interphase, each chromosome is duplicated so each consist of 2 sister chromatids
- chromosomes pair up with homologous pairs
- 2 divisions- each with 4 stages
First meitotic division: - Prophase 1
- Metaphase 1
- Anaphase 1
- Telophase 1
May be brief interphase
Second meiotic division: - Prophase 2
- Metaphase 2
- Anaphase 2
- Telophase 2
Takes place in a plane at right angles to that of meiosis 1
Cytokinesis may occur at end of 2nd division
25
Meiosis- P1
- chromatin condenses, each chromosome supercoils- can take u stains and be seen with light microscope
- nuclear envelope breaks down
- spindle threads of tubulin protein form the centriole (animal cells)
- chromosomes come together in their homologous pairs - each member of the pair consists of 2 chromatids
- crossing over non-sister chromatids wrap around each other and may swap sections so alleles are shuffled
26
Crossing over diagram
27
Meiosis- M1
- pairs of homologous chromosomes, still in their crossed-over state, attach along the equator of the spindle
- each attaches to spindly by its centromeere
- homologous pairs arranged randomly- members of each pair facing opposite poles of the cell- arrangement is independent assortment
- way they line up in M1 depends how they will segregate independently during A1
28
Meiosis- A1
memebers of each pair of homologous chromosones pulled apart by motor proteins that drag them along tubulin threads of the spindle
- the centromeres don't divide, each chromosome consists of 2 chromatids
- the crossed over areas separate from eachother- resulting in swapped areas of chromosome and allele shuffling
29
Meiosis T1
- in most animal cells, 2 new nuclear envelopes form around each set of chromosomes, cell divides by cytokinesis
- short interphase when chromosomes uncoil
- each new nucleus contains half the original number of chromosomes, but each consists of 2 chromatids
- in most plant cells, the cell goes straight from A1 to P2
30
Meiosis P2
- if the nuclear envelopes have reformed, they now breakdown
- the chromosomes coil and condense, each consisting of 2 chromatids
- the chromatids of each chromosome are no longer identical due to crossing over in p1
- spindles form
31
Meiosis M2
- the chromosomes attach by their centromere to the equator of the spindle
- the chromatids of each chromosome are randomly arranged
- the way they are arranged will determine how the chromatids separate during A2
32
Meiosis A2
- centromeres divide
- the chromatids of each chromosome are pulled apart by motor proteins that drag them along the tubulin threads of the spindle, towards opposite poles
- the chromatids are therefore randomly segregated
33
meiosis T2
- nuclear envelopes form around each of the 4 haploid nuclei
- in animals, the 2 cells now divide to give 4 haploid cells
- in plants a tetrad of 4 haploid cells is formed
34
How does meiosis produce genetic variation
- crossing over in P1 shuffles alleles
- independent assortment of chromosomes in A1 leads to random distribution of maternal and paternal chromosomes of each pair
- independent assortment in A2 leads to further random distribution of genetic material
- haploid gametes are produced which undergo random fusion with gametes derived from another organism of the same species
35
Mitosis vs meiosis diagram
36
Mitosis vs meiosis numbers of chromosomes/chromatids
37
Describe the need for cell differentiation and specialisation and how this differs across different organisms
- within a single-celled organism, such as amoeba, the division of labour is determined by the organelles- each of which has specific function
- single celled organisms are small have large surface are a to volume (SA/V) ratio so that oxygen can diffuse across and waste products can diffuse out via the same (plasma) membrane
- multicellular organism- larger- smaller SA/V ratio
- means most of cells arent in direct contact with external environment
- need specialised cells to carry out particular functins- cant rely on dissfusion alone
38
Describe how cell differentiation happens
- all multicellular eukaryotic organisms start life as a single undifferentiated cell- Zygote- resulted from an ovum (egg cell) is fertilized by a spermatoxoon and the 2 haploid nuclei fuse to give a cell with a diploid nucleus
- the zygote is not specialised- all genes in its genome are able to be expressed
- also able to divide by mitosis
- it is a stem cell
- after several mitotic divisions, an embryo forms, containing many different embryonic stem cells
- these embryonic stem cells differentiate as certain genes are switched off and others may be expressed more, so that:
- the proportion of the different organelles differs from those of other cells
- the shape of the cell changes
- some of the contents of the cell change
- due to differentiation, each cell type us specialised for a particular type of function
39
Name specialised amimal cells
- erythrocytes
- neurophills
- spermatozoa
- epithelial cells
40
Erythrocytes: function, where they come from, adaptions
In Mammals:
- erytrocytes- carry oxygen from lungs to respiring cells
- derived from stem cells in the mone marrow
Adaptions:
- Very small- (about 7.5 micrometers in diameter)- large SA/V ratio- means oxygen can diffuse across their membranes and can easily reach all regions inside the cell, bioconcave shape also increases SA/V ratio
- flexible- well developed cytoskleton- allws them to change shape so hey can twist and turn as they travel through very narrow capillaries
- most of their organelles are list in difefrentiation- have no nucleus, mitochondria or endoplasmic reticulum, very little cytopasm- more space for many haemoglobin molecules housed within them- haemoglobin synthesised within immature erythrocytes, whilst they still have their nucleus, ribosomes and rough endoplasmic reticulum
41
Neutrophils: function, where they come from, adaptions
- ingest invading pathogens
- derived from stem cells in the mone marrow
- make up about 50% of cells in your body
Adaptions:
- about twice the size of erythrocytes, each contains a multilobed nucleus
- attracted to and travel towards infection sits by chemotaxins
- function is to ingest bacteria and some fungi by phagocytisis
42
Spermatozoa adaptions
- many mitochondria- carry out aerobic respiration- the ATP provides energy for the undulipodium to move and propel the cell towards the ovum
- small and long- can move easily
- once the spermatozoon reaches the ovum, enzymes are released from the acrosome (a specialised lysosome)- the enzymes digest the outer protective covering of the ovum, allowing the sperm head to enter the ovum
- the head f the sperm contains the haploid male gamete nucleus and very little cytoplasm
43
Where are epithelial cells found, name 2 types
- epithelium is lining tissue
- found on out and inside of your body
- makes up the walls of the alveloli and capillaries, and lining of intestines
- squamous epithelial cells- plattened in shape
- cillated epithelial cells- have cillia
44
Name specialised plant cells
- Palisade cells
- guard cells
- root hair cells
- xylem and phloem
45
Palisade cells adaption
Adapted for photosynthesis because:
- long and cylindrical- pack together quite closely but with a little space between them for air to circulate; carbon dioxide in these air spaces diffuses into the cells
- have large vacuole so that the chloroplasts are positioned nearer to the periphery of the cell, reducing the diffusion distance for carbon dioxide
- contain many chloroplasts- carry out photosynthesis
- contain cytoskeleton threads and motor proteins to move the chloroplasts- nearer to upper surface of the leaf when sunlight intensity is low, but further down when it is high
46
Guard cells location, how they work, adaptions
- lower epidermis- do contain chloroplasts but don't photosynthesis as don't have enzymes needed for 2nd stage, found in pairs
- light energy used to produce ATP
- ATP actively transports potassium ions from surrounding epidermal cells into guard cells- lowers their water potential
- water now enters the guard cells from neighbouring epidermal cells, by osmosis
- the guard cells swell, but at the tips the cellulose cell wall is more flexible, and it is more rigid where it is thicker- tips bulge, and the gap between them (stoma) enlarges
- as these stomata open, air can enter the spaces within the layer of cells beneath the palisade cells
- gaseous exchange can occur, and carbon dioxide will diffuse into the palisade cells- as they use it for photosynthesis, this maintains a steep concentration gradient
- oxygen produced during photosynthesis can diffuse out of the pallisade cells into the air spaces and out through the open stomata
- when the stomata are open, water vapour also exists from them (part of transportation)
47
Where you find root hair cells, how they're adapted
Epidermal cells on the outer layer of young plant roots
- hair-like projection greatly increases the surface area for absorption of water and mineral ions, such as nitrates, from the soil into which it projects
- mineral ions are actively transported into the root hair cells- lowering the water potential within them and causing water to follow by osmosis, down the water potential gradient
- have special carrier proteins in the plasma membranes in order to actively transport the mineral ions in
- these cells also produce ATP- needed for active transport
48
Define a tissue
A group of cells working together to perform a certain function
49
4 main tissue types in the body
- epithelial (lining)
- connective tissues- hold structures together- e.g. blood, bone, cartilage
- muscle tissue- made of cells that are specialised to contract and cause movement
- Nervous tissue- made of cells specialised to conduct electrical impulses
50
Epithelial tissue location, structure, cell cycle, functions, example
Location:
- covers and lines free surfaces in the body such as the skin, cavities, of the digestive and respirator system (gut and airways)
, blood vessels, heart chamers and walls of organs
Charachteristics:
- made up almost entirely of cells
- cells are very close to each other to form continuous sheets
- adjacent cells are bound together by lateral contacts, such as tight junctions and desmosomes
- no blood vessels within epithelial tissue, cells receive nutrients by diffusion from tissue fluid in the underlying connective tissue
- some epithelial cells have smooth surfaces, but some have projections either cilia or microvilli
Cell cycles:
- Short
- divide up to 2/3 times a day to replace worn or damaged tissue
Specialised for functions of:
- protection, absorption, filtration, excretion and secretion
Alveoli:
- walls one cell thick- single layer of flattened squamous epithelial cells- short diffusion distance
51
Describe charachteristics and exaamples of connective tissue
- widely distributed in body
- consist of a non-living extracellular matrix containing proteins (collagen and elastin) and polysaccharides (such as hyaluronic acid, which traps water)
- this matrix separates the living cells within the tissue and enables it to withstand forces such as weight
- blood, bone, cartilage, tendons, ligaments are examples
- skin also contains connective tissue
52
Cartilage- charachteristics, types
- immature cekks in cartilage are called chrondroblasts
- they can divide by mitosis and secrete the extracellular matrix
- once the matrix has been synthesised, the chrondroblasts become mature, less active chondrocytes, which maintain the matrix
3 Types:
- hyaline cartilage- forms the embryonic skeleton, covers the ends of long bones in adults, joins ribs to the sternum, found in nose, trachea (forming the C-shaped rings that keep it open) and larynx
- fibrous cartilage- occurs in discs between vertebrae in the backbone (spine) and in the knee joint
- elastic catilage- makes up the outer ear (pinna) and the epiglottis (flap that closes over the larynx when you swallow)
53
Describe charachetristics and functios of muscle tissue
- well vascularised (has many blood vessels)
- mussscle cells are called fibrres- they ate elongated and contain special organelles called myofiaments made of the proteins actin and myosin- allow muscle tissue to contract
Functions:
- skeletal muscles, packaged by connective tissue sheets and joined to bones by tendons- when they contract, they cause bones to move
- cardiac muscle- makes up the walls of the heart- allows the heart to beat and pump blood
- smooth muscle- occurs in the walls of the intestine, blood vessels, uterus and urinary tracts- propels substances along these tracks
54
Name main types of plant tissue
- epidermal tissue
- vascular tissue
- meristematic tissue
55
Describe epidermal tissue
- equivaknet to epithelial tissue in animals
- consist of flattened cells that, apart from the guard cells, lack chloroplasts
- these form a protective covering over leaves, stems and roots
- some epidermal cells also have walls impregnated with a waxy substance, forming a cuticle- particularly important to plants that live in dry places as the cuticle reduces water loss
56
Describe vascular tissue
Concerned wit transport- 2 types (both present in vascular bundles):
- xylem- carry water and minerals from roots to all parts of the plant
- phloem- sieve tubes transfer the products of photosynthesis (mainly sucrise sugar), in solution, from leaves to parts of the plant that don't photosynthesis such as roots, flowers and growing shoots
57
Describe/give charachteristics of meristematic tissue
- contains stem cells
- from this tissue that all other plant tissues are derived by differentiation
- found in root and shoot tips, and in the cambium of vascular bundles- meristems
The cells in meristems:
- have thin walls containing very little cellulose
- don't have chloroplasts
- don't have a large vacuole
- can divide by mitosis and differentiate into other types of cells
58
Describe how xylem and phloem derive from meristem
As most plant cells mature, they develop a large vacuole and rigid cellulose cell wall- these prevent the cell from dividing.
However, plants need to grow and produce new cells- which arise at the meristems, by mitosis.
Some Cambium cells differentiate into xylem vessels:
- lignin (a woody substance) is deposited in their cell walls to reinforce and waterproof the; however, this also kills the cells
- the ends of the cells break down so that the xylem forms continuous columns with wide lumens to carry water and dissolved minerals
- the ends of the cekks break down so that the xylem forms continuous columns with wide lumens to carry water and dissolved minerals
Othher cambium cells differentiate into phloem sieve tubes or companion cells:
- sive tubes lose most of their organelles, and sieve plates develop between them
- companion cells retain their organelles and continue metabolic functions to provide ATP for active loading of sugars into sieve tubes
59
Define an organ
A group of tissues working tigeter ti perform the same function
60
Name 4 plant organs
- leaf
- root
- stem
- flower
61
Leaf- main functions
Photosynthesis
62
Root main functions
- anchorage in soil
- absorption of mineral ions and water
- storage- e.g. carrot, parsnip, dahlia and swede roots store carbohydrates
63
Stem main functions
- support
- holds leaves up so that they are exposed to more sunlight
- transportation of water and minerals
- transportation of products of photosynthesis e.g. potato tubers store starch, rhubarb stems store sugars and polysaccharides
64
Name 11 organ systems
- digestive
- circulatory
- respiratory
- urinary
- integumentary s
- musculo-skeletal
- immune
- nervous
- endocrine
- reproductive
- lymph
65
Digestive system- organs/tissues involved, examples of life processes carried out
- oesophagus, stomach, intestines plus associated glands, liver, pancreas
- nutrition to provide ATP and materials for growth and repair
66
Circulatory system- organs/tissues involved, examples of life processes carried out
- heart and blood vessels
| - transport to and from cells
67
Respiratory system- organs/tissues involved, examples of life processes carried out
- airways and lungs
- diaphragm and intercostal muscles
- breathing and gaseous exchange excretion
68
urinary system- organs/tissues involved, examples of life processes carried out
- kidneys, uterus, bladder
| - excretion and osmoregulation
69
integumentary system- organs/tissues involved, examples of life processes carried out
- skin, hair and nails
| - waterproofing, protection, temperature regulation
70
musculoskeletal system- organs/tissues involved, examples of life processes carried out
- skeleton and skeletal muscles
| - support, protection and movement
71
Immune system- organs/tissues involved, examples of life processes carried out
- bone marrow, thymus gland, skin, stomach acid, blood
| - protection against pathogens
72
Nervous system- organs/tissues involved, examples of life processes carried out
- brain, spinal cord, nerves
| - communication, control, coordination
73
Endocrine system- organs/tissues involved, examples of life processes carried out
- glands that make hormones e.g. thyroid, ovaries, testes, adrenals
- communication, control, coordination
74
Reproductive system- organs/tissues involved, examples of life processes carried out
- testes, penis, ovaries, uterus, vagina
| - reproduction
75
Lymph system- organs/tissues involved, examples of life processes carried out
- lymph nodes and vessels
| - transports fluid back to the circulatory system and is also important in resisting infections
76
Define organ system
- a number of organs working together to carry out an overall life function
77
Define STEM cells
Unspecialised cells able to express all of their genes and divide by mitosis - capable of becoming any cell in the organism
78
Types of stem cells
pluripotent (totipotent)- van express all genes, can become any cell in the organism- can divide by mitosis and provide more cells that can differentiate into specialised cells for growth and tissue repair
- multipotent- specific range
- unipotent- 1 type
79
Sources of STEM cells
- embryonic stem cells- present in early embryo formed when zygote begins to divide
- stem cells in umbilical cord blood
- adult stem cells (also found in infants and children) are found in developed tissues such as blood, brain, muscle, adipose, tissue and skin, amongst the differentiated cells- like repair system as renewing source of undifferentiated cells
- induced pluripotent stem cells (iPS) cells by reprogramming differentiated cells to switch on certain key genes and become undifferentiated
80
List potential uses of stem cells
- bone-marrow transplants
- drug research
- developmental biology
- repair of damaged tissue or replacement of lost tissues
81
Describe use of stem cells for bone marrow transplants
- treat diseases of the blood (e.g. sickle cell anaemia and leukaemia) and immune system (e.g. severe combined immunodeficiency or SCID)
- also used to restore the patients blood system after treatment for specific types of cancer, where the patients bone marrow cells can be obtained before treatment, stored, and then put back inside the patient after treatment
82
Describe use of stem cells for drug research
- if stem cells can be made to develop into particular types of human tissue, then new drugs can be tested first on these tissues, rather than on animal tissue
83
Describe use of stem cells for developmental biology
- can use stem cells to rsearch developmental biology and enable a better understanding of how multicellular organisms develop, grow and mature
- they can study how these cells develop to make particular cell types (e.g. blood, bone muscle and skin) and can learn how each cell type functions and see what goes wrong when they are diseased
- they are trying to find out if they can extend the capacity that embryos have for growth and tissue repair, into later life
84
Describe use of stem cells for repair of damaged tissue or replacement of lost tissues
Hard to culture stem cells in a lab so this research is ongoing. Also necessary to find out which cytokine cell-signalling molecules ate needed to direct the differentiation of stem cells into particular cell types
- stem cells have been used to treat mice with type 1 diabetes bey programming iPS cells to become pancreatic beta cells- research is underway to develop such treatment in humans
- bonemarrow stem cells can be made to develop into liver cells (hepatocytes) and could be used to treat liver disease
- stem cells directed to become nerve tissue could be used to treat Alzheimer and Parkinson diseases it to repair spinal cord injuries
- stem cells may be used to populate a bioscaffold of an organ, and then directed to grow into specific organs for transplanting. This is called regenerative medicine. If the patients cells are obtained, reprogrammed to become iPS cells, and then used to make such an organ, there will be no need for immunosuppressant drugs
- stem cells may eventually be used to treat many conditions, including arthritis, strokes, burns, vision, and hearing loss, duchene muscle dystrophy and hear disease
85
Issues with stem cell research
- ethics- some people disagree with using embryos for research as are potential for life
