unit 2: Flashcards
1
Q
A
2
Q
microscopes:
A
-these include light and electron microscopes
-light microscopes have a magnification up to x1500 but electron microscopes can have a mag. up to x500,000
-electron microscopes use a beam of electrons and the specimen must be placed in a vacuum
-electron microscopes include: SEM and TEM
-seen microgrpahs are 3D and very striking but have lower magnification compared to TEM micrographs
3
Q
magnification:
A
a measure of how much bigger an image is compared to the object
magnification = magnified image/actual size of image x 100
-learn units!!!!
4
Q
resolution:
A
a measure of how far apart two objects must be before they are see separately
5
Q
light microscopes: lenses
A
light source -> condenser lens -> specimen lens (specimen has to be a very thin layer, no more than one cell thin) -> objective lens (magnifies and inverts image) -> eyepiece lens (focuses the image in the eye, you can change the eyepiece lens to change magnification)
6
Q
light microscopes - pros and cons
A
pros:
-we can see living organisms and cells, although some times the preparation of the sample kills them
-relatively cheap
-portable and relatively light
cons:
-artifacts appear from preparation and staining, these are results of the processing of the sample that can be mistaken for actual characteristics of the specimen
-low magnification and resolution (compared to electron microscopes)
7
Q
staining:
A
-we can use stains to differentially color parts of the cells, or even distinguish between living cells and dying cells
-hematoxylin stains the nuclei of plant and animal cells purple, blue or brown
-methylene blue stains the nuclei of animal cells blue
-acetocarmine stains dividing chromosomes in animal and plant cells
-iodine stains starch-containing organelles in plant cells blue-black
-trypan blue stains dead cells but not living cells
8
Q
eukoryotic cells:
A
-membrane bound
-have a nucleus
9
Q
membranes:
A
membranes are important as an outer boundary to the cell and also as the many intracellular (internal) membranes
10
Q
protoplasm:
A
comprises cytoplasm + nucleus and many cellular structures called organelles
11
Q
the nucleus:
A
-it is usually the largest organelles in the cell
-it is usually spherical in shape, surrounded by a double nuclear membrane with holes or pores
-it comprises of nucleic acids (DNA and RNA)
-the DNA is bonded to basic proteins called histones to form chromatin
-the nucleus can control events in the cytoplasm
-aslo in the nucleus is at least one nucleolus- an extra-dense area of almost pure DNA and protein
12
Q
the mitochondrion:
A
-are tiny rod-like structures presumed to have originated as symbiotic eubacteria living inside early eukaryotic cells
-are the ‘powerhouses’ of the cell that is sites for cellular respiration which produced ATP used to drive cellular functions
-have an outer and inner membrane and contain genetic material so that when a cell divides, the mitochondria replicate themselves
-the inner membrane is folded to form cristae, which give a very large surface area, surrounded by a fluid matrix
13
Q
centrioles:
A
-there is ususally a pair of centrioles near the nucleus
-each centriole consists of a bundle of nine sets of tubules and is about 0-5 um long by 0.2 um wide
-the centrioles are involved in cell division producing spinal fibres to attach to the centromere for sister chromatids to be pulled apart
14
Q
80S and 70S ribosomes:
A
-this is where protein synthesis occurs
-ribosomes are made from ribosomal RNA and protein, and consist of a large subunit and a small subunit
-eukaryotic cells contain 80S ribosomes which are made up of a 40S small subunit and a 60S large subunit
-the ratio of RNA : protein in 80S ribosomes is 1:1
-70S ribosomes are usually found in prokaryotic cells and consist of a small 30S and a larger 50S subunit
-the ratio of RNA : protein in 70S ribosome is 2:1
15
Q
lysosomes:
A
-lytic enzymes
-important in breakdown of phagocytosized food in single celled organisms and destruction of worn out cells in your body
-appear as dark, sphreical bodies in the cytoplasm of most cells and they contain a powerful mix of digestive enzymes
-important in programmed cell death is known as apoptosis
16
Q
rough and smooth endoplasmic reticulum:
A
-the ER network links with the membrane around the nucleus, and is divide into the rough and smooth endoplasmic reticulum
-the RER is covered with granules, which are 80S ribosomes, the RER has a large surface area for the synthesis of all proteins -> it then stores and transports the proteins within the cell after they have been made
-the SER is not covered by ribosomes and is also involved in synthesis and transport, but in this case of steroids and lipids
17
Q
the Golgi apparatus:
A
-it is made up of stacks of parallel, flattened membrane pockets formed by vesicles from the endoplasmic reticulum fusing together
-proteins are brought to the Golgi apparatus in vesicles that are separate from the RER where they were made
-the proteins are modified as they travel through the Golgi apparatus
-carbohydrate is added to some proteins to form glycoproteins such as mucus
18
Q
bacterial cell walls:
A
-all bacterial cells have a cell wall
-the cell wall prevents the cell swelling and bursting as it takes in water by osmosis
-it also mantains the shape of the bacteriium, and gives support and protection to the contents of the cell
-all bacterial cell walls have a layer of peptidoglycan making it to have a net-like structure
-some bacteria have a capsule around their cell walls that protects the bacterium from phagocytosis by white blood cells
-it also covers the cell markers on the cell membrane that identify the cell
19
Q
pilli and flagella:
A
-pilli are thread-like protein projections on the surface of some bacteria
-they are used for attachment to a host cell and for sexual reproduction
-flagella are made of a multi-stranded helix of the protein flagellin
-the flagellum moves the bacterium by rapid rotations- about 100 times per second
20
Q
70S ribosomes:
A
-they have two subunits, the smaller is 30S and the larger is 50S
-they are involved in the synthesis of proteins in a similar way to eukaryotic ribosomes
21
Q
prokaryotic cells: cell surface membrane
A
-it is similar in both structure and function to the membranes of eukaryotic cells
22
Q
nucleoid:
A
-an area in the bacterial cell where this DNA tangle is found
-the genetic material of a prokaryotic cells consists of single circular strand of DNA, which is not contained in a membrane bound nucleus
23
Q
plasmids:
A
-are much smaller circles of DNA down
-they code for a particular aspect of the bacterial phenotype in addiion to the genetic information in the nucleoid
24
Q
Gram positive VS Gram negative:
A
-Gram positive (such as MRSA, multi-resistant Staphylococcus aureus) have a thick layer of peptidoglycan and substances such as teichnoic acid
-the thick layer traps the crystal violet/blue iodine stain and prevents it from decolouring when alcohol is added, so they don’t absorb the red safranin
-therefore, gram-positive appear blue after this function
-Gram negative (such as Escherichia coli) have a thinner teichnoic acid-free peptidoglycan layer surrounded by two membranes, with the external one being rich in lipopolysaccharides
-they crystal violet/blue iodine stain is washed off with alcohol, so they absorb the red safranin and appear red under a microscope
25
bacterial shapes:
-bacteria can be classified by their shapes:
-cocci -> sphere-shaped
-bacilli -> rod-shaped
-vibrios -> comma-shaped
-spirilla -> twisted
26
bacterial metabolism:
-bacteria can be classified by their metabolism (how they get the energy from organic compounds):
-obligate aerobes: can only respire aerobically, so they need oxygen to survive
-obligate anaerobes: oxygen kills them, they only respire anaerobically
-facultative anaerobes: can survive with or without oxygen as they respire both aerobically and anaerobically
27
classification of cells:
cells -> tissues -> organ -> organ system -> organism
28
tissues:
-tissues are groups of cells that all develop from the same kind of cell
-tha main types of tissue include; epithelial tissues, connective tissue, muscle tissue and nervous tissue
29
epithelial tissue 1.0:
-they originate from the basement membrane
-they are made of one or more types of cell, that sit tightly together
-they form layers that protect the cells and tissues below them
-there are 6 main types, with different functions and locations in the body
-called simple squamos
-forms the lining of blood vessels and alveoli
30
epithelial tissue 2.0:
-cuboidal
-columnar
-surfaces of many tubes in the body, such as kidney tubules
31
epithelial tissue 3.0:
-ciliated
-cilia wave regularly to move substances across tubes
-goblet cells associate with ciliated cells, and produce mucus for protection
-glandular
-found in oviducts and the respiratory tissues
32
epithelial tissue 4.0:
-compound stratified
-found in surfaces that need resist scratching, such as the skin
-cells are formed on the germinal layer and as they rise they will eventually die
33
organs:
-an organ is a structure made of several different tissues grouped into a structure so that they can work effectively together to carry out a particular functions
-plants have cells grouped into tissues and organs
e.g. organs -> stem, roots, leaves
34
organ systems:
-in animals, often several organs work together as an organ system to perform large-scale functions in the body
-for example, the digestive system includes, the stomach, oancreas and small and large intestines
35
what are chromosomes?
-a chromosome is made up of a mass of coiled threads of DNA and proteins, chromosomes carry the genetic information
-in a cell that is not actively dividing, we cannot see them easily or identify them as individual structures
-when the cell strats to actively divide, the chromosomes condense - they become much shorter and denser and we can identify individual chromosomes
-the DNA winds around the histones to form dense clusters known as nucleosomes
-human cells contain 46 chromsomes
36
the cell cycle:
-cell divide on a regular basis to bring about growth and asexual reproduction
-interphase is a period of non-division when the cells increase in mass and size, carry out normal cellular activities and replicate their DNA ready for division
-this is followed by mitosis, a period of active division
-the cytokinesis when the new cells separate
-the lengths of the cell cycle is variable, it can be very rapid, taking 24 hours or less, or it can take a few years
37
Interphase:
cell grows to its normal size after cell division, and synthesises important substances, e.g. proteins
38
Growth 1 phase:
-gap after cell division and before S phase
-46 chromosomes and chromatid at this phase
-prepares for growth and DNA synthesis (S phase) by producing RNA, proteins and enzymes
-new organelles are formed
-if there are insufficient growth factors, or when cell has reached its maximum size, cell will not divide and remain in G1
39
S phase:
-synthesis of DNA, each chromosome consists of two identical chromatids
-46 chromosomes and 92 chromatid at this stage
-chromatin also replicates along with DNA so histones are replicated
40
Growth 2 phase:
-gap after S phase and before nuclear division (prepares for mitosis)
-new DNA checked, and errors are repaired
-centrioles replicate
-food storage is increased
41
mitosis:
-it is the complex series of movements that occur during cell division as the chromosomes compete for space in the middle of the nucleus and then pull apart to opposite ends of the cell
-mitosis produces two identical daughter cells
-the sequence of events include: prohase, metaphase, anaphase and telophase
42
importance of mitosis:
-mitosis is how organisms grow and replace old cells
-it is also the method which organisms use for asecual reproduction
-this is advantageous if identical offspring are required however, environemntal changes can affect survival
43
prophase:
-initial phase of mitosis
-chromatin condenses into chromosomes
-the nucleoulus and nuclear envelope breaks down
-the centrioles pull apart and begin forming the spindle
44
metaphase:
-thanks to the formation of the spindle (bu the action of the centrioles, which have moved to opposite poles of the cell), choromosomes will line up in the equator of the cell, known as the metaphase plate
-in plant cells this process is identical, despite not having centrioles
-the spindle associates with the centromeres of the chromosomes to line them up
45
anaphase:
-chromosomes are separated into single-chromatid chormosomes, thanks to the spindle fibres pulling them towards each pole of the cell
-the microtubules contain contractile fibers that allow them to pull from the chromosomes
-this requires ATP and takes a matter of a few mins
46
telophase:
-opposite to prophase
-the DNA uncoils to chromatin
-nuclear envelopes form around the two new sets of chromosomes
-the nucloulus is formed
-the spindle is broken down
47
cytokinesis:
-the cytoplasm divides
-in animal cells, a ring of contractile fibres tightens around the centre of the cell similar to a belt tightening around a sack of flour
-these fibres seem to be the same as those found in animal cell muscle cells
-they continue to contract until te two cells have been separated
-in plant cells, the division of the occurs differently
-a cellulose cell wall builds up from the inside of the cell outwards
48
sexual reproduction:
-this is the production of a new individual from the joining (fusion) of two specialised cells called gametes
-sexual reproduction produces individuals that are not genetically the same as either of their parents, but contain genetic information from both
-sexual reproduction relies on two gametes meeting and fusing
-it usually involves special sexual organs
-due to increased genetic variation, it improves survival of offspring in a changing environment
49
gametes:
-most body cells chromosomes occur in pairs with two full sets of chormosomes is called diplois (2n) and the number of chromosomes in a diploid cell is characteristic for that species
-gamete cells contain haploid (n) nuclei with one set of chromosomes (half of the full chromosomes number)
-sexual reproduction occurs when two haploid nuclei fuse to form a new diploid cell called zygote in a process called fertilization
50
Meosis:
-meosis is a reduction division and it occurs only in the sex organs
-in animals, the gametes are formed directly from meiosis
-its the basis of the variation that allows species to evolve
-in meiosis, two nuclear division produce four haploid daughter cells, each with its own unique combination of genetic material
-it is divided into meiosis 1 and 2
51
Meiosis 1: prophase 1
-chromosomes condense and can be visible
-the nuclear envelopes breaks down
-the centrioles move to opposite sides of the cell
-spindle fibers begin to form
-crossing over occurs
52
Meiosis 1: metaphase 1
-chromosomes move to the metaphase plate
-homologous chromosomes pair up
-spindle fibers attach to the centromere of each chromosome
-independent assortment occurs
53
Meiosis 1: anaphase 1
-homologous pairs are pulled to opposite ends of the cell by contraction of spindle fibers
-the centromeres are not divided
54
Meiosis 1: telophase 1 + cytokinesis
-the spindle fibers break down
-the chromosomes gather at the poles
-the cytoplasm begin to divide
55
Meiosis 2: prophase 2
a new spindle forms around the chromosomes
56
Meiosis 2: metaphase 2
metaphase 2 chromosomes line up at the equator
57
Meiosis 2: anaphase 2
-centromeres divide
-chromatids move to the opposite poles of the cells
58
Meiosis 2: telophase 2 + cytokinesis
-a nuclear envelope forms around each set of chromosomes
-the cytoplasm divides
59
importance of meiosis:
-meiosis reduces the chromosome number in gametes from diploid to haploid
-this makes sexual reproduction is possile with offspring being only haploid
-it is also the main way in which genetic variation is introduced to a species
-variation is a result of crossing over and independent assortment
60
crossing over:
-it occurs in prophase 1 of meiosis
-large, multi-enzyme complexes 'cut and join' bits of maternal and paternal (non-sister) chromatids together
-the points where the chromatids break are called chiasmata
-the exchange of genetic material leads to added genetic variation and errors in the process could lead to a mutation
61
independent assortment:
-this occurs in metaphase 1 of meiosis as the chromosomes line up on the metaphase plate
-the maternal and paternal chromosomes are distributed into the gametes completely at random
62
gamete formation in mammals:
-gametes make sexual reproduction possible and are formed in gametogenesis
-both mitosis and meiosis have a role in gametogenesis
-mitosis provides the precursor cells
-meiosis causes the reduction of genetic material in divisions that result in gametes haploid)
-in females, mitotic division occur before birth to form diploid primary oocytes, which remain inactive until puberty
-the second meiotic divisions are only completed if the ovum is fertilised
63
the male gamete (spermatozoa):
-acrosome: stores digestive enzymes
-the nucleus: contains a haploid number of chromosomes
-mitochondria: provide ATP for lashing of the tail
-tail: made of microtubules to produce whip-like movements of the tail to keep the mature sperm in suspension to swim towards the ovum
64
the female gamete (ovum):
-genetic material at end of first stage of meiosis
-cell surface membrane of oocyte
-cytoplasm with many food reserves
-zona pellucida, a clear protective 'jelly like' layer that surrounds the oocyte
65
gamete formation in plants:
-it occurs in two phases of a plants life cycle:
-the sporophyte generation is diploid and produces spores by meiosis
-the resulting gametophyte generation is haploid and produces the gametes by meiosis
-the main body of the plant that we see is the diploid sporophyte
-the haploid gametophytes are reduced to part of the contents of the anther and the ovary
66
the pollen grain:
-it contains two haploid nuclei:
-pollen tube nucleus
-cytoplasm
-thick reistant wall
-cell surface membrane
-generative nucleus
67
the ovules:
-the embryo sac contains 8 nuclei but 7 cells
-the three antipodal cells are rich in nutrients like lipids and they supply nutrients to the whole gametophyte and during embryo development
-the two polar nuclei to form one secondary nucleus which fuses with one male nucleus resulting into a triploid (3n) endosperm, the endosperm provides nourishment later during germination
-the two synergid cells guide the pollen tube towards the egg cell
-the single eff cell fuses with one male nucleus to form the zygote:
-three antipodal cells
-two polar nuclei
-female gamete (egg cell)
-two synergids
68
fertilisation in humans:
-the ovum is fully viable and able to receive the male gamete for only a few hours
-the sperm will survive a day or two in the female reproductive tract
-as soon as the heads of the sperm touch the surface of the ovum, the acrosome reaction is triggered
-enzymes released from the acrosome, which digest the follicle cells and the zona pellucida
-eventually, one sperm will wriggle through the weakened protective harness and touch the surface membrane of the oocyte, this has several almost instantaneous effects
-the second meioitic division takes place providing a haploid ovum nucleus to fuse with the haploid male nucleus
69
Fertilisation: mammals
-cells are surrounding the secondary oocyte release chemicals, attracting the sperm cells
-once sperm reaches the secondary oocyte, an acrosome reaction occurs
-enzymes are released, they begin digesting the follicle and zona pellucida layers
-the enzymes are released by exocytosis from the sperm head
-once digested, the sperm nucleus de condenses, then, it’s released by exocytosis into the secondary oocyte release chemicals
-the cortical reaction takes place, releasing enzymes that cause hardening of the zona pellucida, this prevents other sperm cells from entering
-the genetical material is taken into the cell by endocytosis, this triggers Meiosis II to form an ovum
-the haploid nuclei fuse, forming a diploid zygote
70
Fertilisation: plants
-once a pollen reaches the stigma surface, it starts germinating after absorbing the sugar solution on its surfaces
-the pollen tube starts growing towards the embryo via chemical stimulus
-the tube nucleus releases enzymes by exocytosis, allowing the formation of a tube
-as the tube elongates, nutrients are absorbed along the way
-the generative nucleus divides producing 2 sperm nuclei
-the pollen tube reaches the micropyle (the entrance to the embryo), penetrating the embryo sac wall
-double fertilisation occurs, which 1 nucleus fuses with the egg cell, forming a diploid zygote- the other nucleus fuses with the 2 polar nuclei, forming a triploid endosperm nucleus
-after fertilisation, the ovule becomes a seed, the zygote becomes an embryo, and the endosperm becomes food storage
71
gene expression in action:
-in a multicellular organism, every cell contains the same genetic information but different cells perform different functions
-they differentiate and develop into different tissues and organs
-as this cell differentiation occurs, different types of cell produce more and more proteins which are specific to their cell type
-this means that different genes must be expressed in different types of cell
72
how do genes control the phenotype?
-each gene is found at a particular place the chromosome and this location is known as the locus of the gene
-each gene has at least two different forms, known as alleles
73
mutiples alleles:
-pea shape and colour and the inheritance of cystic fibrosis and colour blindness are determined by 2 alleles
-however, some features are determines by multiple alleles which means there are more than 2 possible variants
-no matter how many possible alleles there are, any one diploid individual will only inherit two of them
-these alles are still inherited in the same way, although the patterns of dominance may be more complex
-e.g. human ABO
74
ABO inheritance:
-genotype: OO -> phenotype: blood group O
-genotypr AO or AA -> phenotype: blood group A
-genotypr: BO or BB -> phenotype: blood group B
-genotype: AB (codominance) -> phenotype: blood group AB
75
polygenic traits:
-these are traits determined by many different genes interacting with one another
-eg: eye colour, skin colour, intelligence etc
-digenic inhertiance occurs when two different genes are inherited completely independently
-in some cross experiments, the expected rations may be different from observe ratios because:
-the sample size may be small
-the process in random and some unexpected results occur
-linkage in genes
e.g experimental errors
76
ratios in dihybrid inheritance:
inheriting two pairs of contrasting characteristics at the same time
9:3:3:1 and 3:1
77
linkage in fruit flies:
genes found on the same chromosome are inherited as a single unit, this shows linkage
9:3:3:1
78
identifying linked genes:
-genes for different characteristics which are found on the same chromosome are linked
-they are inherited as if they were a single gene
-the tightness of the linkage of a pair of genes is related to how close together on the chromosome
-genes that are very close together are less likely to be split during the crossing over stage of meiosis than genes that are further apart
-if the genes are further apart, crossing over between them is more likely to occur
79
Siamese cats:
-they have dark 'points' on the ears, the muzzle and the paws
-their genotype suggests that they should have dark fur all over the body as a result of melanin which is produced in a process involving the enzyme tyrosinase
-however, a mutation in Siamese cats results in a version of tyrosinase that is inactive at normal body temperatures and only works at lower temperatures
-so in Siamese cats, the fur over the majority of the body is pale, but at the extremities-the ears, paws and nose where the temp is lower - the enzyme is not denatures and as a result the fur is dark
80
controlling gene expression:
-the expression of a gene involves two key stages- transcription from DNA to messenger RNA (mRNA) and translaton from nRNA to proteins
-exerting controls at any of the stages of the process gives control over the expression of the genes
-in addition, the proteins can be changed once they have been synthesised, giving another level of control over the expression of a gene
81
transcription factors:
-the most common way of controlling gene expression is by switching on and off the transcription of certain genes
-transcription describes the process by which the genetic code of the DNA is copied to a complementary strand of mRNA before protein synthesis can occur
-transcription factors are proteins that bind to the DNA in the nucleus and affect the process of transcribing the genetic material
-all transcription factors have regions that enable them to bind to specific regions on the DNA known promoter sequences found just above the starting point for transcription upstream of the gene
82
cont. transcription factors:
-some transcription factors stimulate the transcription of a region of DNA simply by binding to a DNA promoter sequence
-this stimulates the start of transcription of that area of the DNA
-other trasncription factors bind to regions known as enhancer sequences and regulate the activity of the DNA by changing the structure of the chromatin, making it more or less open to RNA polymerase
-an open chromatin structure is associated with active gene expression; closed chromatin structures are associated with gene inactivity
83
RNA splicing:
-several processes occur which modify it before it lines up on the ribosomes, so it referred to as pre-mRNA
-the modifications to the pre-mRNA always involve the removal of the introns and, in some cases, some of the exons are removed as well
-enzyme complexes called spliceosome join together the exons that are to be transcribed and produce the mature, functional mRNA
-the spliceosomes may join the same exons in a variety of ways in a process known as RNA splicing
84
Post translation control:
-further modification of proteins may also occur after they have been synthesised
-a protein that is coded for by a gene may remain intact or it may be shortened or lengthened by enzymes to give a variety of other proteins
85
Epigenetics: DNA methylation
-the addition of the methyl group always occurs at the site where cytosine occurs next to a guanine in the DNA chain with a phosphate bond between them
-the methyl group is added by a DNA methyltransferase enzyme
86
Epigenetics: Histone modification
-histone actylation: adding acetyl groups to lysine in the histone structure this usually opens the structure, activating the chromatin for transcription
-histon methylation: adding methyl groups to lysine in the histone, depending on the position of the lysine the methyl group is added to, methylation can lead to activation or deactivation, methylation is often linked to silencing genes
87
Epigenetics; Non-coding RNA
have been associated with epigenetic control, but scientists are not yet sure what they do
88
Cell diferentiation:
-cell diferentiation occurs when unspecialised cells switch different genes on off as needed to become specialised cells
-chemical stimulus (e.g. demethylation/transcription factor)
-certain genes activated/switched on
-mRNA produced from these genes
-translation of mRNA to form polypeptide/protein
-permanent modification of the cell
89
early stages of development:
fertilisation -> 2-cell stage embryo -> 4-cell stage embryo -> embryo is a hollow ball of cells (all totipotent) -> blastocyst (pluripotent)
90
types of stem cells: embryonic stem cells
by the blastocyst stage, when the embryo is implanted in its mother's uterus, the inner cells of this ball are pluripotent
91
types of stem cells: umbilical cord stem cells
the blood that drains from the placenta and umbilical cord after birth is a rich source of pluripotent stem cells
92
types of stem cells: adult stem cells
-some adult stem cells (somatic stem cells) remain as undifferentiated cells and are found among the normal differentiated cells in a tissue or organ
-therefore for development into an organism, gene expression occurs by switching on and off certain genes
-transcription factors are produced, epigenetic control through DNA methylation and histone modification occur and non-coding RNAs are part
-this leads to the different shapes and functions of cells in the fetus
93
stem cell therapy:
-both embryonic and adult stem cells can be used
-however, due to ethical issues with embryonic stem cells, adult stem cell have been used more successfully
-therapeutic cloning is a technique that will hopefully be used for producing large quantities of healthy tissues
-this could be used to treat health confditions like Alzeihmer's, type 1 diabetes etc
94
benefits and pitfalls of stem cell therapy:
-this can overcome organ rejection if the patient's own cells are used
-scientists are not completely sure how to switch genes on and off
-some cells become cancerous
95
induced pluripotent stem cells:
-it involves using adult stem cells and reprogramming then to become pluripotent again, producing stem cells without the use of embryos
-this overcomes ethical objection from using embryonic stem cells
-no risk of rejection
-cells can be made into any body cell
-however, the cells have a tendency to become cancerous
96
potential benefits from stem cell therapy:
-Pakrinson's disease: dopamine producing nerve cells are lost, sufferers have uncontrolled tremors, muscle rigidity
-however, one dopamine producing cells are restored, dopamine can be produced and the tremors disappear
-Type 1 diabetes: insulin secreting cells replaced using iPS, insulin production resumes
-damaged nerves: this can lead to paralysis, however, iPS can regenerate the nerve cells and health can be stored
-organ donation: various organs could be produced using iPS to overcome shortage and rejection
97
the plant cell wall:
-it gives the plant cells shape (turgidity of cells)
-it gives plants their strength and support (lignification)
-it is mostly made of insoluble cellulose
-the plant cell wall is usually freely permeable to everything that is dissolved in water
-addition to lignin (to cell walls of woody plants) and suberin (to cell walls of cork tissues) reduces their permeability to water
98
layers of plant cell walls:
-the middle lamella is the first layer: it is mostly made of pectin, a polysaccharide that acts like glue and holds the cell walls of adjacent plant cells together
-pectin binds calcium to form calcium pectate which join adjacent cells when the cell first divides
-the cellulose micro fibrils and the matrix build up on both sides of the middle lamella, this is the primary cell wall
-a secondary cell wall builds up, with the cellulose microfibrils laid densely at different angles to each other
-hemicelluloses help to harden it further, lignin is then added to the cell walls to produce wood
-in plants, there are many long cells with heavily lignified cellulose cell walls to make plant fibres
99
cellulose:
-cellulose is the main compound in plant cells
-it consists of long chains of beta glucose joined bby 1,4 glycosidic bonds
-in cellulose, one of the monomer units has to be turned round (inverted) so the bonding can take place
-the hydroxyl (-OH) groups stick out on both sides of the molecule, this allows cross linking between chains as hydrogen bonds form
-this makes cellulose a material with great strength so, it is used for strength and support in plants
-cellulose molecules do not coil ir spiral like starch, they remain as very longe, straight chains
100
plasmodesmata:
-in primary cell walls (non lignified) materials are exchanged through special cytoplasmic bridges called plasmodesmata where cells are thinner
-during cytokinesis, the two daughter cells do not separate completely, and threads of the cytoplasm remain between them -> the interconnected cytoplasm of the cells is called the symplast
-when the secondary thickening takes pace, hemicelluloses and lignin are deposited in the cell wall making it thicker
-however, thickening doesn't occur around the plasmodesmata, leaving thin area called pits
-there is no cytoplasm in the xylem cells but the pits allow water to move between the xylem vessels
-they are important in mantaining a flow of water at even pressure through the plant
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permanent vacuole:
-a vacuole is any fluid filled space inside the cytoplasm which is surrounded by a membrane
-it can occupy up to 80% of the volume of a plant cell
-it is surrounded by a specialised membrane called the tonoplast that controls the movements of ubstances into and out of the vacoule and so it controls the water potential of the cell
-the vacoule is filled with cell sap, a solution of various substances in water
-it causes water to move into the cell by osmosis, and this means the cytoplasm is kept pressed against the cell wall, this keeps the cells turgif (swollen) and the whole plant stays upright
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chloroplasts:
-they are found in cells from green parts and they enable plants to photoysynthesis
-cells in flowers, seeds, roots, transport tissues and internal tissues of the stem have no chloroplasts
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similarities of chloroplasts and mitochondria:
-they are large organelles
-they have a biconvex shape with a diameter of 4-10 um and are 2-3 um thick
-contain their own DNA
-they are surrounded by an outer membrane
-they have an enormously folded inner membrane that gives a great surface area where enzyme-controlled reactions take place
-they are though to have been free-living prokaryotic organisms that were engulfed by and became part of other cells more than 2000 million years ago (endosymbiosis)
-however, chloroplasts contain chlorophyll but mitochondria do not
-chlorophyll is the green pigment that traps sunlight for photosynthesis to occur
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amyloplasts:
-they are colourless organelles that store starch
-the starch can be converted to glucose and used to provide energy when the cell needs it
-large numbers of amyloplasts are found in areas of a plant that store starch, for example potato tubers
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function of stems:
-they support, to hold the leaves in the best position for obtaining sunlight for photosynthesis
-they support the flowers to maximises the likelihood of pollination
-they help the movement of materials around the plant by providing a route along which the products of photosynthesis are carried from the leaves to other parts of the plant where they are needed
-they move water steadily through the stems from the roots up to the leaves, and carry mineral ions which are needed for synthesis of more complex chemicals
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tissues of plant stems:
-plant stems are made up of:
1. xylem
2. phloem
3. sclerenchyma
4. collenchyma
5. parenchyma
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parenchyma:
-they are unspecialized cells
-they can be modified for storage and for photosynthesis
-they can be modified to form collenchyma and parenchyma
-they give buoyancy to aquatic plants
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collenchyma:
-they have thick cellulose primary cell walls, which are thicker at their corners
-this gives the tissue its strength
-they are found around the outside of the stem, just inside the epidermis
-they give plenty of support but remain living, so they strech as the lant grows and provide flexibility
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sclerenchyma:
-they are a type of modified parenchyma (packing) tissu found in plant cstems
-they are found around the vascular bundle in older stems and in leaves
-all sclerenchyma cells have strong secondary walls made of cellulose microfibrils positiones at right angles to each other
-lignin is deposited on the cell walls of these fibres in a spiral or a ring pattern, and this makes the fibres strong but also flexible
-sclerenchyma cells can also become completely impregnates with lignin and form sclereids
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transport tissues in plants:
-xylem tissue carries water and dissolved mineral ions from the roots to the photosynthetic parts of the plant
-phloem is living tissue made of phloem cells which transport the dissolved product of photosynthesis (surcrose) from the leaves to where it is needed for growth or storage or starch
-cambium is a layer of unspecialised cells which divide, giving rise to more specialised cells that form both the xylem and the phloem
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xylem:
-they start off as living tissue
-the first xylem the plant makes is called the protoxylem, it can stretch and grow because the walls are not fully lignified
-moew lignin is incorporated into the cell walls as the stem ages and the cells stop growing -> the cell becomes impermeable to water and other substances, this lignified tissue is callled the metaxylem
-the end walls between the cells mostly break down so the xylem forms hollow tubes which go from roots to the tip or the stems and leaves
-water and mineral ions are transported from the roots to the leaves and shoots in the transceription stream
-water moves out of the xylem into the surrounding cells through the specialised pits in the walls of the xylem vessels
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phloem:
-phloem is never lignified, so it is living tissue
-phloem transports organic solutes like surcrose up and down the plant in an active transport process called translocation
-the phloem consists of many cells joined to make very long tubes that run from the highest shoorts to the end of the roots
-the walls between the cells become perforated, creating specialized sieve plates and the phloem sap moves through the holes in these plates
-the phloem sieve tube becomes a tube filled with phloem sap and the mature phloem cells have no nucleus
-they are closely associated with cells called companion cells, they are linked to the sieve tube by many plasmodesmata
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importance of water and mineral ions:
-water is needed for:
-photosynthesis
-support (turgidity to mantain cell structure)
-transport (ions and organic molecules)
-cooling (evaporation during transpiration)
-the need for mineral ions:
-nitrates (amino acids, proteins)
-defiency leads to stunted growth, yellow leaves
-calcium: needed for calcium pectate in the middle lamella
-defiency leads to yellow crinkly leaves
-magnesium: needed for chlorophyll
-defiency leads to yellow areas on leaves and slow growth
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plant fibers:
-plant contain fiber in the cellulose cell walls of their cells
-they are ususally long sclerenchyma cells or xylem tissues
-they are usually very touch and strong -cannot be easily broken down by pulling
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processing fibers:
-fibers can be produced by two methods:
-manufacture (using chemicals/enzymes)
-traditional (relying on natural decomposers)
-the processed material is then spun into fibers
-spinning creates long continuous threads from short fibers
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wood:
-it is made up of lignified cellulose fibers embedded with hemicelluloses and lignin
-the cellulose makes wood reistant to compression
-wood has a flexible matrix of intermeshing cellulose fibers
-nails can be hammered through wood without cracking
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biplastics and biological plymers:
-most plastics are made from fossil fuels and are therefore not sustainable
-bioplastics are sustainable since they are made from renewable resources like sugarcane, maize, etc.
-bioplastics are biodegradable since they can be broken down by microorganisms
-biological polymers are polymers made from biological materials, they are sustainable, biodegradable
-bioplastics can be used in drug delivery, drinking cups, computer casing
-when bioplastics are burned, they do not increase the net carbon dioxide in the atmosphere
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plants vs microbes:
-bacteria and fungi can infect plants, so, plants can produce chemical (antimicrobials) against infection
-we can obtain some medicines against human infections from plants
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bacterial growth:
-bacteria require sveral conditions for suitable growth
-temperature, nutrients, pH, oxygen concentration
-in culturing bacteria, aseptic technique should be used
-to prevent contamination from other bacteria
-to prevent growth of pathogenic bacteria
-non-pathogenic bacteria can mutate and become pathogenic
-growth medium can be solid or liquid
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antimicrobials plant extracts:
-plants produce antiseptic compounds
-many drugs againts human infections have been extracted out of plants
-extraction ensures that a known dosage of the medication will be given to the patient, also, other plant materials that are not medicinal can be removed out
-to extract plant antimicrobials, a suitable solvent must be chosen, the solvent dissolves the plant compound to maximized extraction
-a solvent can also break down the membranes of the cells and vacuoles to release the extract
-the plant material can be ground or cut into smaller pieces to increase the amount extracted
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testing promising new drugs:
-the new drug should be:
-effective: cures, prevents or relieves symtoms of disease
-safe: not toxic and not have unnacceptable side effects
-stable: can be stored without decomposition under normal conditions
-easily taken into and excreted from the body once it has done its job
-can be cheaply made on large scale
-researchers use computer models to fit structures on active sites of enzymes and receptor proteins involved in the progression of a disease
-once a promising compound is discovered, it is patented
-the patent is valid for 20 years
-testing begins on cell structures, tissue cultures and then whole organs in the lab
-if successful, animal testing can then be done
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drug development and animal testing:
-a good delivery system has to be found:
-tablets
-liquid medicine
-injections
-nasal sprays
-the drug should be stable
-the drug should not break down into something toxic
-if the drug is changed into something else in the body, it should be excreted safely
-due to ethical concerns, animal trials can be replaced by tissue cultures
-however, animal trials must be done before moving to human trials
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clinical trials:
-it is divided into 3 phases:
-phase 1:
-carried out on a few healthy volunteers
-to determine any unkown isde effects in the human body
-phase 2:
-carried out on about 100-500 patient volunteers
-to determine the ideal dosage. effectiveness and any side effects
-phase 3:
-carried out on thousands of patient volunteers (>5000)
-to confirm the effectiveness and safety of the new drug
-to monitor if there is a statistically siginificant difference btween the new medicine and currently available drugs
-placebp is given to eliminate bias + phase 2 and 3 are double blind
-results from each phase are assesed to evaluate the beneficial effecrs againts harmful side effects
-a decision can then be made to liscence the drug
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biodiversity:
-it is a measure of the variety of living organisms and their genetic differences
-to quiantify biodiversity, we need a way of identifying the different groups of organisms
-organisms are classified into groups based on their similarities and differences
-classification provides an internationally recognized wa of identifying different groups of organisms
-a good classification system clarified ancestral relationships
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the main taxonomic groups:
-organisms are classified into kingdoms, phylum, class, order, family, genus and species
-based on 3 domain system, there are 6 kingdoms
-archae domain: contains only one kingdom -> the archaebacteria
-bacteria domain: this contains only one kingdom -> the eubacteria kingdom-these are the normal bacteria
-eukaryota domain: these contain four kingdoms
-protista: autotrophs and heterotrophs, some are plant like (green-bown algae) and others are animal-like (amoeba)
-fungi: all are heterotrophs, most are saprotrophs, some are parasitic -> they have chitin cell walls
-plantae: all are autotrophs that contain chlorophyll (they include flowering and non-flowering plants)
-animalia: all are heterotrophs, they include vertebrates (fish amphibians, reptiles, birds, mammals) and invertebrates (mollucks, insects, worms, enchinoderms)
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the morphological species concept:
-most organisms are classified based on their morphology
-this is based on observable similarities and differences between organisms
-however, the appearance of an organism can be affected by many different things and there can be huge amount of variation within a group of closely related organisms
-e.g. sexual dimorphism: where a great deal of differences exist between the male and female of a species, this weakense the morphological concept
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the reproductive and biological species concept:
-according to this, a species is a group of organisms with similar characteristics that interbreed to reproduce fertile offspring
-limitations:
1. all the organisms in a species cannot attempt to interbreed to produce fertile offspring because they do not all live in the same area
2. if two individuals from different populations mate, they are considered the same specied if fertile offspring are produced and genes are combined or 'flow' from the parents to the offspring
-horses and donkeys look similar, however, they mate to produce sterile offspring (the mule)
-lions and tigers are different species but if a tiger and a lion mate, most of the offspring (ligers) are fertile, this weakens this defintion of a species
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sophisticated defitions of species:
-to help overcome these limitations, two slightly more sophisticated edfinitions of species based on reproductive capability are:
-a groups of organisms with similar characteristics that are all potentially capable of breeding to produce fertile offspring
-a group of organisms which genes can flow between individuals
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other definitions of species:
-ecological species model: based on the ecological niche occupied by an organism
-mate-recognition model: based on unique fertilization systems-including ating rituals and behaviour
-genetic species model: based on DNA evidence
-more reliable
-however, a decision has to be made on how much genetic different there shoyld be for two organisms to be classified as differen species
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limitations of the species model:
-finding a mate: some organisms have never been observed mating, setting up breeding programs to observe this could be done however it is time consuming and expensive
-closely related species often interbreed and produce fertile hybrids, should hybrid be reocgnized as different speies? when should that be?
-many organisms like bacteria, fungi and oritists do not reproduce sexually, so, definitions of a species relating to reproductive behaviours is irrelevant to them
-fossil organisms can't reproduce and there is usually no accessible DNA, however, these tooo need to be classified
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