Module 2 Flashcards
Sample preparation
FIXING: chemicals like formaldehyde used to preserve specimens
DRY MOUNT: embedded in wax and cut with microtome knife to preserve shape. cryostat cuts specimens frozen in liquid nitrogen
WET MOUNT: suspended in water or oil and cover slip placed on at an angle. drop of stain at one edge and paper towel at other to draw stain across.
SQUASH SLIDES: wet mount is prepared and lens tissue used to press down cover slip
SMEAR SLIDES: edge of slide smears sample onto another slide
Why is staining needed
Examples of stains
images have low contrast as the cells absorb little light
resolution is limited by wavelength of light an diffraction
cell structures often transparent but different ones take up different stains due to chemical nature
Eosin stains cytoplasm
methylene blue stains DNA
electron microscopes use heavy metal compounds that absorb electrons like phosphotungstic acid
Cell theory
- all living things consist of one or more cells
- new cells are formed by the division of preexisting cells
- the cells contain information that acts as instructions for growth and can be passed onto new cells
Magnification
how many times larger an image is compared to the actual object itself
size of image/size of object WILL I AM
resolution
the ability to distinguish between 2 things very close together (limited by diffraction of light ass cases through lenses and samples)
Units
1 meter
- 001 millimetres
- 000001 micrometers
- 000000001 nanometers
measuring cells method
An eyepiece graticule is fitted into microscope eyepiece (100 EPU)
its scale must be calibrated for each magnification using a stage micrometer
it has 100 divisions and it 1mm long, so each division is 10 micrometers
1 graticule division= number of micrometers/ number of graticule divisions
Compound microscope
2D high magnification (1500) low resolution (0.2 um) living or dead eyepiece lens then objective lens to change magnification using visible light
Laser scanning confocal microscope
3D
colour
laser beams focused by dichromatic mirrors
specimens tagged with fluorescent dye and laser light causes it to give off light which is shone onto detector
small and portable
Scanning electron microscope
3D high magnification (500,000) high resolution (less than TEM 0.002um) dead specimen black and white electromagnetic lenses beam of electrons knocks electrons off specimen which are collected in a cathode ray tube forming a image of exterior artefacts hard to use and large vacuum mounted on aluminium stubs and coated in gold
Transmission electron microscope
2D high magnification (1,000,000) high resolution (0.0002um) electromagnets focus a beam of electrons transmitted through specimen denser parts absorb more so darker ultramicrotome used to create thin slices vacuum films of collodion on copper grids
microfilaments: monomer structure function size
MONOMER- actin STRUCTURE- contractile fibres made from 2 intertwined strands. grown and shrink as monomers added and removed. networks form a matrix FUNCTION- maintain cell shape contraction cell movement cytokinesis of cell division SIZE- 7nm
intermediate filaments: monomer structure function size
MONOMER- fibrous proteins like keratin STRUCTURE- fibres would into thicker cables and form a dense network within and around nucleus FUNCTION- maintain cell shape give strength to cell as resists tension anchor nucleus and organelles SIZE- 10nm diameter
Microtubules
MONOMER- globular tubular proteins (alpha and beta dimers)
STRUCTURE- hollow tubes which grow or shrink in length as subunits are added or subtracted from ends
FUNCTION-
maintain cell shape
act as tracks for movement of organelles
cilia and flagella motility
spindle fibres in cell division
SIZE- 25nm diameter
Types of protein threads
Types of microtubules (made of microtubules)
Microfilaments, intermediate filaments, microtubules
Centrioles, flagella, cilia
Centrioles
- structure
- function
- location
- numbers
FUNCTION- organising spindle in cell division
STRUCTURE- ring of 9 triplets of microtubules
LOCATION- near nucleus in cytoplasm
NUMBERS- in pairs at right angles to each other
Flagella
What is different about bacteria?
FUNCTION- move cells like sperm
STRUCTURE- ring of 9 pairs of microtubules surrounding a pair in the centre
LOCATION- on surface of cells
NUMBERS- 1 long one sometimes 2
no microtubules in bacteria though as prokaryotes don’t have organelles or cytoskeleton
Cilia
FUNCTION- wafting liquids across cell
STRUCTURE- ring of 9 pairs of microtubules surrounding a central pair
LOCATION- surface of cells
NUMBERS- usually shorter and in large numbers
cell wall structure and function
STRUCTURE- made of cellulose microfibrils embedded in a layer of pectins (adhesive) and hemicelluloses (fluid)
calcium pectate cements one cell to the next
may also contain plasmodesmata- a cytoplasmic link between cells
FUNCTION- provides share and support
protection against pathogens
lets substances in and out
Division of labour
- mRNA copy of the gene is made in nucleus
- mRNA leaves nucleus (MRNA nucleotide goes in) through nuclear pore
- mRNA attaches to a ribosome which reads gene to assemble protein into correct 3D shape
- protein molecules are pinched off in vesicles and travel towards the Golgi apparatus on the cytoskeleton
- vesicles fuse with Golgi and become part of it
- Golgi processes and packages insulin molecules , adding stuff like carbohydrates through an enzyme which makes a glycoprotein
- packaged insulin molecules pinched off in vesicles and move to surface membrane
- fuse with cell surface membrane
- cell surface membrane opens to release molecule to outside
Features of prokaryote (bacteria)
- 1-5um
- 1 membrane- cell wall made of peptidoglycan formed from aa and sugars
- polysaccharide capsule helps it cause disease
- no membrane bound organelles or nucleus
- ribosomes 70S (80S in eukaryote as bigger and dense to make more complex proteins)
- DNA in cytoplasm in a loop- nucleoid
smaller loops of DNA called plasmids - mesosomes are enfolded regions of the cell membrane where ATP is produced- site of respiration. increase SA for enzymes
- flagella are attached to the plasma membrane by a basal body and rotated by a molecular motor. the main body is a filament and hook, which gets energy to rotate from chemiosmosis unlike ATP in eukaryotic
- pilus used for attachment and shorter and straighter than flagella
- genes in chromosomes groupes into operons so a number of them can be switched off at once
Endosymbosis
the theory that mitochondria and chloroplasts and maybe other eukaryotic organelles were formerly free-living bacteria. They were taken inside another cell as an endosymbiont. Eventually evolved to form eukaryotic cells.
Advantages and disadvantages of prokaryotes
DISADVANTAGES:
some are resistant to antibiotics - MRSA. this is coded for on plasmid DNA and can be transferred between cells
ADVANTAGES:
food industry for cheese and yogurt
used in mammalian intestines to digest food and break down vitamin K
skin on flora to help prevent microorganisms getting on
used in sewage treatment and natural recycling
Difference between prokaryotic and eukaryotic cells
Feature Prokaryotic cell Eukaryotic cell Cell size: P-Small (1-5micro) E-Larger (20-40 (or 100) micro) Genetic material: P-Nucleoid. 1 circular chromosome free in cytoplasm but super coiled to make compact. E-True nucleus. Multiple linear chromosomes wrapped around proteins called histones creating chromatin, which coils and condenses to form chromosomes. Organelles: P-No E-Membrane bound/many Ribosomes: P- 70S (smaller)- 10-20nm E-80S (larger)- 25nm Respiration: P-Mesosomes E-Mitochondria Flagella: P-Simple, no microtubules (20nm) E-Complex, microtubules (200nm) Photosynthesis: P-May take place on unstacked membranes E-Chloroplasts Examples: P-Bacteria E-Plant, animal, fungi Cytoskeleton: P-Present E-Present, more complex Reproduction: P-Binary fusion E-Asexual or sexual Cell type: P-Unicellular E-Uni or multi cellular
What are the 2 nucleic acids
deoxyribonucleic acid
ribonucleic acid
polynucleotides
What is in the nucleotide
- phosphate group- PO4 2-, an inorganic negative acid. bonds to carbon 5 and 3
- organic nitrogenous base containing 1 or 2 carbon rings and nitrogen
- pentose sugar
each component is joined by a strong covalent bond in 2 condensation reactions
(image of phosphate, sugar and base joined)
Types of bases
Purine: Adenine and Guanine
Pyrimadine: Cytosine, Uracil and Thymine (only one carbon ring- longer word but smaller molecule as its been CUT)
(draw out images of the bases)
purine bonds to pyrimidine so its symmetrical
Types of bonding
-nucleotides are joined by phosphodiester bonds to form a sugar phosphate backbone
chains of nucleotides join together to form nucleic acids
only nucleotides of the same sugar can join
-hydrogen bonds hold the double helix 3D structure between the bases. easily broken and reformed to allow DNA to replicate. complementary base pairing A-T 2 hydrogen bonds, C-G have 3.
What is the name for how the strands are held together
anti-parallel strands
Similarities and differences between DNA an RNA
S-Pentose sugars
D-deoxyribose sugar and ribose sugar on carbon 2
S-nitrogenous bases
D-RNA has U instead of T
S-sugar phosphate backbone
D-Double/single strand
S- Phosphodiester bonds/condensation reactions
D-3 types of RNA-messenger, ribosomal and transfer
S-nucleotides
D-DNA/RNA nucleotides
S-Order of nitrogenous bases forms a code on the nucleic acid (DNA+mRNA)
D-DNA stores genetic information long term and bases code for aa which make proteins/RNA doesn’t store code but copies it-protein synthesis
D-DNA is big and stable RNA is small and unstable especially mRNA
D-DNA in nucleus/ RNA in nucleolus and cytoplasm
What is ATP and it uses
- phosphorylated nucleotides that are made up of a ribose, adenine (nitrogenous base) and 3 inorganic phosphates
energy storage molecules where energy can be released by breaking bonds between phosphates.
-immediate store as used up as soon as made. instability of phosphate bonds in ATP means not good long term store.
-A small amount of energy is needed to break (hydrolyse) the bond, but lots is released when the phosphate undergoes other reactions involving bond formation 30.6KJmol-1 - occurs simultaneously with energy requiring reactions
-energy used in the breakdown of these molecules (respiration) is used to create ATP by attaching a phosphate to an ADP molecule-phosphorylation
Properties of ATP
- Small- moves easily in and out of cells
- Water soluble- energy requiring processes occur in aqueous environments
- Contains bonds between phosphates with intermediate energy- large enough for useful cellular reactions but not large enough that energy is wasted as heat
- Releases energy in small quantities- for same reason as above
- Easily regenerated- can be recharged with energy
Semi-conservative DNA replication
- The DNA helix unwinds
- The 2 polynucleotide strands of DNA separate as the hydrogen bonds between the bases are broken by the enzyme helicase, which catalyses reactions to break them.
- This unzips the DNA exposing the nitrogenous bases
- Each new strand now acts as a template for the formation of a new molecule of DNA
- Free DNA nucleotides base pair with the unpaired complementary bases. Complementary base pairing ensures exact copies are made
- Then phosphodiester bonds form between the phosphate of one DNA nucleotide and the sugar of the next
- The enzyme DNA polymerase catalyses the condensation reaction to covalently bond each nucleotide to the next. The sugar phosphate backbones of each new DNA strand are joined to form a DNA polymer
- 2 genetically identical DNA molecules are formed, each containing one strand from the parent DNA and a new complementary strand- half parental DNA Is conserved.
The strand that codes for a protein to be synthesised is a sense strand and rund from 5’ to 3’. The other strand is from 3’ to 5’ and is complementary to the sense strand and is also known as the antisense strand or the template strand. RNA is same bases as sense.
DNA replication
- The copying of DNA so that following cell division each new cell will have a full copy of all the original DNA. It is semi conservative replication, and produces geneticall identical sister chromatids
- occurs during S phase
- Must be copied accurately to conserve genetic information
- Mutations are random an spontaneous changes in the sequence of bases in the DNA
Experiment showing semi-conservative replication
Started growing bacteria in a medium containing heavy nitrogen isotope 15N, which the bacteria used to make nucleotides. The bacteria where then transferred to a normal 14N growth medium, and DNA samples were extracted over time and centrifuged. This separated the DNA according to density.
The lowest strip contains purely 15N, the medium is hybrid DNA with 1 parental strand and 1 new DNA strand and the top is light DNA with just new strands.
- Bacteria are used for this experiment as the replicate very fast so multiple generations and changes can be seen in a short period of time
- Few ethical concerns
- Reproduce asexually so less variation
Genetic code to polypeptides
Types of polypeptides
A gene is a sequence of bases in DNA that codes for the codon which determine the sequence of aa in the primary structure of the polypeptide. this codes for enzymes which catalyse reactions to build a whole person.
DNA contains the genetic code which codes for the synthesis of all polypeptides
its contained in the nucleus to be conserved and protected
Types of polypeptides are:
- Structural proteins (keratin, collagen, actin, myosin)
- Channel proteins
- Enzymes
- Cell surface receptors
- Electron carriers
- Haemoglobin
- Antigens, immunoglobulins
Genetic code to polypeptides
A gene is a sequence of bases in DNA that codes for the codon which determine the sequence of aa in the primary structure of the polypeptide. this codes for enzymes which catalyse reactions to build a whole person.
in-between genes is non coding DNA
DNA contains the genetic code which codes for the synthesis of all polypeptides. genome is entire sequence of DNA with 25,000 genes
its contained in the nucleus to be conserved and protected
Types of polypeptides are:
- Structural proteins (keratin, collagen, actin, myosin)
- Channel proteins
- Enzymes
- Cell surface receptors
- Electron carriers
- Haemoglobin
- Antigens, immunoglobulins
Features of the genetic code
o A triplet code
o Is degenerative (more than 1 codon codes for the same aa, which means mutations can be silent if the new triplet code codes for the same amino acid as the previous one)
o It has punctuation
o It is widespread but not universal ( most organisms have same code but different sequence of bases)
o A non overlapping code (always in threes ensured by start codon)
There are 4 bases arranged into triplets.
43 =64 options
There are 20 amino acids
64-3 stop codons =61
61-1 met (start codon) = 60 options
Transcription
- The part of the DNA molecule to be transcribed unwinds and unzips as DNA helicase breaks the H bonds between bases, exposing unpaired nucleotides. Happens 3’ to 5’ of template strand.
- Free RNA nucleotides form complementary base pairs with the unpaired bases on the template strand – hydrogen bonds. This starts at 5’ end of nucleotide and 3’ of mRNA
- A binds with U and C binds with G, with 2 and 3 hydrogen bonds, purine to pyrimidine
- Phosphodiester bonds (covalent) form between nucleotides to make the sugar phosphate backbone using the enzyme RNA polymerase. This occurs 5’ to 3’.
- The template and coding strand reform hydrogen bonds, A-T ect.
- The mRNA is complementary to the template strand and a copy of the coding strand
- mRNA leaves to go to the ribosomes through the nuclear pore
tRNA
- made in the nucleus and passes into the cytoplasm
- it is a length of RNA that folds into hairpin shapes to form a clover leaf
- it can bind to a specific amino acid in the cytoplasm where 3 exposed bases are
- it can recognise the specific mRNA codon for the amino acid it carries by having 3 unpaired nucleotide bases at the other end which are anticodons for the amino acid
- the other clover leaf recognises a specific activation enzyme
- is the smallest RNA and there are over 20
After protein synthesis the RNA molecules are degraded in the cytoplasm- the phosphodiester bonds are hydrolysed an the RNA nucleotides are released and reused
Translation
- mRNA attaches to the small subunit of a ribosome in the groove exposing 6 bases of the mRNA to the large subunit. Several ribosomes may attach to the mRNA at once forming a polysome. This means many identical polypeptides can be synthesised at once. and each makes a bit of the polypeptide all one polypeptide or several different
- the first exposed mRNA codon is always AUG (start codon methionine)
- the tRNA molecule with the amino acid metaphase has an anticodon complimentary to the 1st codon, and lines up in position P.
- complimentary base pairs form H bonds between the codon and the anticodon (UAC with AUG)
- another tRNA (pro) forms complimentary base pairs with the next codon in the ribosome at position A
- the enzyme peptidyl transferase forms a peptide bond between the two amino acids (met and pro)
- the first tRNA is released and leaves the ribosome without its amino acid
- the next ribosome moves along the mRNA 3 bases exposing the next codon
- the second tRNA molecule (pro) is now in position P
- a new tRNA molecule pairs with the mRNA in position A bringing its amino acid (Tyr)
- a growing polypeptide is formed in this way until a stop codon is reached
- a stop codon (UAA, UAC or UAG) on the mRNA signals the ribosome to leave the mRNA. These work by having no tRNA with a complementary anticodon or the tRNA is codes for is not carrying an amino acid
- a newly synthesised protein is now complete and can take up its tertiary structure ect. Needed for structure and fucntion
- some proteins need to be activated by cAMP to take a 3D shape that is the best fit to their complementary molecule eg. By binding to an allosteric site on an enzyme
Comparing replication and transcription
R-Both processes have DNA as template but both strands are used as template strands
T-Has a template strand and a coding strand
R-Whole molecule is unzips and unwinds and is replicated
T-Only part of a DNA molecule (gene) unzips and unwinds at a time
R-Activated free nucleotides to bond to, but DNA nucleotides
T-Activated free nucleotides to bond to but RNA nucleotides
R-Both use polymerase to form phosphodiester bonds to produce a backbone but DNA polymerase
T-Both use polymerase but RNA polymerase
R-Both use complimentary bases with hydrogen bonds but AT GC
T- AU GC
R-Product is 2 daughter strands identical to templates
T-Product is 1 mRNA strand
R-DNA stays in nucleus
T-mRNA leaves through nuclear pore to go to cytoplasm
R- both unwinds and unzips
T- unwind and unzip
Protein synthesis
o DNA stays in nucleus
o Proteins are made on ribosomes in the cytoplasm (ribosomes made in nucleolus from rRNA and protein)
o Genetic code is copied to messenger RNA which can leave the nucleus by nuclear pores as its smaller taking the code to the ribosomes transported by the cytoskeleton
Cell cycle
INTERPHASE
Growth 1: normal cell growth and specialisation. proteins from which organelles are synthesised are produced
Synthesis: DNA replication
Growth 2: synthesis of organelles so there’s enough in new cells. DNA starts to coil into visible chromosomes at end.
MITOSIS (cytokinesis)
Difference between mitosis and cytokinesis
mitosis is when the nucleus splits (growth, repair and asexual reproduction)
cytokinesis is when rest of cell splits and is the end of mitosis
how are cells formed
by asexual reproduction or form a zygote from a female and male gamete
differentiation
the process by which a cell develops to become more distinct in form and function
Cell cycle checkpoints
enzymes check replicated DNA for errors
if errors are detected they are repaired or the cell destroys itself to stop mutations being passed on
G1:chromosomes checked for damage and DNA repaired before S phase. If the cell doesn’t satisfy the requirements of the checkpoint, then it enters the resting state G0.
s: check that all chromosomes have been replicated- the cycle will stop if not
G2:another check for DNA damage that may have occurred during replication, and cycle may be delayed to repair
Metaphase:check whether chromosomes have attached correctly to spindle fibres before anaphase
interphase
the part of the cell cycle where the cell is not undergoing cell division
what is G0 and why does it happen?
The phase when the cell leaves the cycle either temporarily or permanently. It does this because:
• Differentiation: a cell that becomes specialised to carry out a particular function is no longer able to divide so will not renter the cycle. red blood cells can’t divide as they loose their nucleus in development
• The DNA may become damaged so is no longer viable and cant divide so enters permanent cell arrest
• The majority of normal cells only divide a limited number of times and eventually become senescent. As you age, the number of these cell in your body increases leading to age related diseases like cancer and arthritis
• Lymphocytes can be stimulated to go back into the cell cycle and start dividing again in an immune response
Homologous chromosomes
homologous chromosomes are 2 chromosomes with the same sequence of genes on them- one from father and one from mother. they may have different alleles
chromatin
DNA wrapped around histone proteins
when it becomes supercoiled it forms visible chromosomes. after G2 as they can’t function when coiled
sister chromatids
before cell divides the DNA replicates (synthesis) producing a chromosome made of a pair of sister chromatids
held together by a centromere. they need to be kept together during mitosis so they can be segregated equally, one to each daughter cell
examples of mitosis
- Replacement of cells EG. outer layer of skin replacement of epidermal cells, red blood cells, intestinal lining cells
- Growth of tissues by producing new extra cells – EG. epithelial tissue, plant meristem cells (stem and root growth).
- Division of zygote into a multicellular organism where, all cells are genetically identical.
- Formation of clones of T and B lymphocytes and plasma cells in the immune response
- Asexual reproduction where mitosis produces individual organisms which are genetically identical to each other (clones) and the parent cell – EG. binary fission in bacteria(not asexual as no nucleus), budding in yeast.
- The production of genetically identical cells in multicellular organisms allows certain cells to retain the ability to develop into any other type if needed as a result of damage.
- Sometimes, abnormal cells divide by mitosis in an uncontrolled way giving rise to tumours, and if the cells are malignant, cancers.
cytokinesis method
the equator of the cell is constricted by a ring of contractile proteins (actin) in the process of cleavage to create 2 cells
in plant cells, cleavage can’t form as there is a cell wall and no centrioles. so vesicles from the Golgi assemble at the equator and fuse with each other and the cell surface membrane to divide the cell
new sections of wall form along the new sections of membrane. if they were formed before daughter cells separated lysis would occur
some vesicles remain intact to make connecting channels- plasmodesmata, through the new cell wall
Mitosis
INTERPHASE: chromosomes replicated and its checked for errors
PROPHASE (plump):
start- chromosomes supercoil, nucleolus starts to disappear, centrioles move to opposite poles and organise formation of microtubules that will form the spindle- spindle starts to form
end- chromosomes consist of a pair of chromatids joined by a centromere, nucleolus disappears and nuclear envelope breaks down
METAPHASE: (middle)
start-Microtubules of the spindle attach to the centromeres from either side which are aligned in the middle. The attachment involves a protein structure on each chromatid called a kinetochore.
end-The microtubules pull in opposite directions on the centromere so that they pull apart
Homologous chromosomes don’t associate.
ANAPHASE: (apart)
start- The chromatids are pulled to opposite poles of the cell by spindle fibres which shorten, centromeres leading (V-shape).
end-chromosomes reach their destination
TELOPHASE: (two)
start-Chromatids now called chromosomes.
The spindle fibres break down. The cells start to constrict around the middle
end-New nuclear envelopes and nucleolus’ form around each group of chromosomes.
The chromosomes slowly uncoil
I Peed on a MAT, C?
Meiosis
• The first stage is when homologous chromosomes are separated into two cells, each containing 1 full set of genes so are haploid due to reduction division
• The second stage is where pairs of chromatids are separated forming 4 haploid daughter cells that are unidentical providing genetic variation
PROPHASE 1: centrioles replicate and move to poles to form spindle, chromosomes condense as sister chromatids after replicating in interphase, nucleolus disappears, and nuclear envelope disintegrates. Crossing over as chiasmata form between homologous pairs of chromosomes (X X) (bivalents when they are close together, 4 chromatids- tetrad). When exchange occurs it forms recombinant chromatids. They may be different alleles of the same gene so sister chromatids are no longer identical.
METAPHASE 1: bivalents line up randomly along the metaphase plate and independent assortment occurs. Microtubules attach to centromeres.
ANAPHASE 1: Separation of homologous chromosomes in each bivalent by contracting microtubules. Each chromosome still has 2 sister chromatids joined together.
TELOPHASE 1: usually telophase 1 and interphase 2 doesn’t occur in plants but in animals chromosomes assemble at each pole, cytokinesis occurs (leaves small cytoplasmic bridges between cells) and new nuclear membranes forms during telophase, chromosomes uncoil and a very rapid interphase may occur.
PROPHASE 2: centrioles replicate and move to poles whilst new spindle fibres form at right angles to previous spindle axis. The chromosomes condense and become visible again and nuclear envelope breaks down if it reformed. No chiasmata
METAPHASE 2: individual chromosomes consisting of 2 sister chromatids line up alone on the metaphase plate. Microtubules attach to centromeres. Independent assortment occurs.
ANAPHASE 2: individual chromosomes are now separated into chromatids by being pulled to opposite poles after division of centromeres
TELOPHASE 2: 4 haploid genetically different cells are produced as chromatids assemble at poles. Chromosomes uncoil and form chromatin again. Nuclear envelope reforms and nucleolus becomes visible.
diagram
Sources of variation
asexual: environmental influences
Sexual: CROSSING OVER
A pair of joined homologous chromosomes – a bivalent with a chiasmata may exchange DNA between non sister chromatids of homologous chromosomes during prophase 1. This creates a new combination of alleles in chromatids, but doesn’t change genetic information as chromosomes have identical sequences. They come together in a process called synapsis
INDEPENDENT ASSORTMENT
The random orientation of homologous chromosomes on the equator in metaphase 1 determines the direction in which the pairs of chromatids move in anaphase 1. different combo of alleles. 2n genetically different gametes could be made where n is the haploid number of chromosomes
In metaphase 2 the random orientation of pairs of chromatids determines which chromosomes migrate to opposite poles of the cell.
FUSION of male (spermatozoa)and female gametes(secondary oocyte) which are genetically different to produce a zygote is completely random creates a large number of allele combinations
RANDOM MUTATIONS
cause different bases so different polypeptides as DNA checks don’t recognise damage
Similarities and differences between mitosis and meiosis
mitosis: no chiasmata form
Meiosis: bivalents are formed when homologous chromosomes are paired up in prophase 1 and chiasmata may form
Mitosis:Individual chromosomes line up along equator in metaphase
Meiosis: Homologous pairs of chromosomes assemble along the equator in metaphase 1
Mitosis:Chromatids are pulled to opposite ends of cell
Meiosis: Homologous chromosomes are pulled to the opposite poles and chromatids stay joined together in anaphase 1
first division ends up with haploid
mitotic index
measures ratio of cells in mitosis to the number of cells counted
used to diagnose cancer as a measure of cell proliferation
high in growing areas like tips and roots
number of cells in mitosis/ total number of cells
blastocyst
a structure formed in the early development of mammals containing embryonic stem cells that will create body cells as well as placenta and umbilical cord. (totipotent) It is not yet implanted in the womb. It is made of an outer layer of cells, a fluid filled space and a group of cells called the inner cell mass, which is where the embryo cells are found
stem cell division
starts with the fertilised egg- 1 cell
divides in 2 to produce 2 daughter cells then divides again and so on
they can self renew by making copies of themselves and also differentiate to make specialised cells. when they divide they produce 2 stem or 2 specialised, not one of each
the DNA in stem cells and the daughter specialised cell is the same, as there are lots of other molecules inside and around cells that can change the way cells behave in the case of differentiated cells
specialised cells can’t divide and make copies of themselves, so stem cells are needed to replace specialised cells that die, get damaged or used up(liver and T cells can)
2 Types of stem cells
embryonic found in the blastocyst
tissue/adult found in tissues of the body(foetus, baby child or adult)
4 types of stem cells
pluripotent:
Can make all types of specialized cells in the body. Embryonic stem cells are pluripotent
Multipotent:
Can make multiple types of specialized cells, but not all types. Tissue stem cells are multipotent as they can only make the kind of cells found in the tissue they belong to- blood cells can make cells found in blood
Totopotent:
can differentiate into all types of specialized cells in the body PLUS cells that are needed during development of the embryo only: placenta, yolk sac, umbilical cord. Eg. Zygote
Unipotent:
can only differentiate into one type of specialized cell. For example, spermatogonial stem cells (found in the testicles) are unipotent because they can only form sperm cells.
Uses of embryonic stem cells
What factors should be considered to assess effectiveness of stem cell therapy?
- To treat diseases
- Understand how diseases develop
- Test drugs in lab
- Umbilical cord stem cells are very good because they are plentiful supply and non-invasive surgery, and can be stored in case the individual ever needs them without rejection
gender, age
Diseases which may betreated by stem cells
diseases which are treated by stem cells
• HEART DISEASE- muscle tissue in the heart damaged from heart attack
• TYPE 1 DIABETES- grow insulin producing cells to transplant into a patient with diabetes
• PARKINSON’S DISEASE- Replacing dopamine producing brain cells that die causing shaking and rigidity.
• ALZHEIMER’S DISEASE- brain cells destroyed from build up of abnormal proteins. Stem cells are beig grown into nerve cells. Hard because damage to brain is widespread.
• MACULAR DEGENERATION- condition responsible for causing blindness in elderly and diabetics. Can grow retinal cells.
• BIRTH DEFECTS- have successfully reversed birth defects in mice
• SPINAL INJURIES- some movement has been restored in rats by introducing stem cells into site of spinal injuries to repair damage
• BLOOD DISEASES- eg. Sickle cell disease using bone marrow and stem cells
CURRENT:
• BURNS- stem cells grow on biodegradable meshes to produce new skin quicker than normal graft process
• DRUG TRIALS- potential new drugs can be tested on cultures of stem cells before being tested on animals and humans
• DEVELOPMENTAL BIOLOGY- the study of the changes that occur as multicellular organisms grow and develop from a single cell like a fertilised egg and why things sometimes go wrong
what are Induced pluripotent stem cells
how may they be used for Alzheimers
• Cells from the body go through genetic reprogramming- certain genes are added to their cell so that the iPS behaves like an embryonic stem cell. These are then cultured in a lab so that they differentiate into specialised cells. From multipotent to pluripotent.
Parkinson’s or Alzheimer:
• Take cells like skin cells from body
• Make iPS cells
• Use those iPS cells to grow specialised cells needed eg. Brain cells. They wouldn’t be rejected as they would be from their own body
What did shimmy yamanaka do
won Nobel prize for adding 4 genes and in a few weeks the cells behaved like stem cells
Ethics of stem cells
- Embryos used to be donated from left over fertility clinics, but the law has changed recently so that embryos can be specifically created in the laboratory as a source of stem cells
- Usually the removal of stem cells from embryos destroys the embryos but techniques are being introduced to prevent damage- moral and religious objections as murder. There are debates over weather the embryo has rights and who owns the genetic material being used for research
- The use of umbilical cord stem cells overcomes the ethical debate, but these cells are only multipotent, not pluripotent like embryonic
- Adult stem cells could also be used but don’t divide as well as umbilical and are more likely to have mutations, therefore iPS is occurring
- Plant stem cells don’t have the same ethical issues and are used to create drugs cheaply and unlimited supply
differentiation
specialisation
The process of physical changes by which a cell develops to become more distinct in form to carry out a particular function
how the physical changes of differentiation allow an organism to perform its function
red blood cell features (erythrocytes)
o Flattened biconcave shape to increase SA to vol ratio for transport of oxygen
o No nuclei or many other organelles increasing space for haemoglobin
o Flexible, elastic membrane to change shape to squeeze through narrow capillaries
o Cytoplsam contains lots of haemoglobin (280mill molecules) pigment binds with oxygen and relases it when concentrations are low
develop large numbers of ribosomes early in differentiation to make haemoglobin
white blood cell features (neutrophil)
o indentation of nucleus to make it multi-lobed so it’s easier to squeeze through small gaps to get to sight of infection. May be due to flexible membrane.
o development of granular cytoplasm contains many lysosomes containing hydrolytic enzymes used to attack pathogens
o Flexible nuclear membrane shape allowing them to penetrate between junctions of the cells of the capillary wall and to form pseudopodia to engulf microorganisms
o Called neutrophils as granules don’t stain darkly with acidic or basic dyes
o Destroy foreign bodies by engulfing them by phagocytosis and secreting enzymes
xylem features
o Responsible for transport of water and minerals throughout plants
o Tissue is composed of vessel elements which are elongated dead cells
o Walls strengthened with lignin providing structural support and waterproof
o Wide lumen and absent end walls allows water flow without blockages
o No cytoplasm as its unnecessary for strengthening and would obstruct water transport
what elements are found in the xylem
o Parenchyma cells are not specialised and form a packaging tissue between other cells
o Vessel elements are the main water transporting cells and have a wide lumen and end walls are perforated or completely absent. Pits allow water to move laterally, which can be helpful for avoiding blockages. Vessels are aligned so are continuous and stretch the length of the plant.
o Tracheid’s transport water in angiosperms they also help strengthen tissue. Don’t have a wide lumen but have perforated end walls and pits where cell wall is very thin, and water can move easily between cells.
o Fibres don’t transport water they just provide support. They have hardly any lumen and are just strips of lignin.
phloem features
o Responsible for transport and of organic nutrients, particularly sucrose, from leaves and stems where it is made by photosynthesis to all parts of plants where it is needed
o Composed of columns of sieve tube cells separated by perforated walls called sieve plates connecting cytoplasm of cells
o Few organelles
o Reduction of cytoplasm means they cannot support themselves so have companion cells
o Plasmodesmata allows molecules to pass between plant cells through cytoplasm
what elements are found in the phloem?
o Sieve tube elements are the cells that transport nutrients
o Companion cells help support the sieve tube elements, and have a large number of mitochondria and ribosomes so we think they play a role in transport
o Phloem parenchyma also are packed between cells
fibres and sclereids with thick. cell walls for support
How are xylem and phloem produced
o Cambium tissue in stems and roots divides to form phloem cells on the outside and xylem on the inside
o Cambium is an example of meristem- undifferentiated plant tissue and is pluripotent
o The production of xylem and phloem is stimulated by hormones.
o The balance of different hormones can shift production between xylem and phloem
o The outer cambium cells produce phloem and the inner produce xylem
o The cells that become xylem lose their cytoplasm and deposit lignin in their cell walls. The end cell walls may be lost.
o The cells that become phloem loos some cytoplasm and organelles and develop sieve plates at the end of cells.
squamous epithelium features
o Made of specialised squamous epithelial cells
o Very thin due to flat/squat cells and is only 1 cell thick, helping rapid diffusion across a surface
o Forms lining of lungs and allows rapid diffusion of oxygen into blood
ciliated epithelium
o Made of ciliated epithelial cells
o Cells have hair like structures called cilia on one surface that move in a rhythmic manner to move substances
o Lines trachea to sweep mucus away from lungs
o Goblet cells are also present releasing mucus to trap any unwanted particles in air like bacteria, so they don’t reach the alveoli
sperm cells
o Male gametes that deliver genetic information to female gamete (ovum)
o Have a flagellum to help with movement
o Contain many mitochondria to supply the energy needed to swim
o Acrosome head contains digestive enzymes released to digest the protective layers around the ovum allowing the sperm to penetrate
Palisade cells
o Many chloroplasts to absorb as much light as possible for photosynthesis. They can also move within the cytoplasm in order to absorb more light
o Cell is tall and thin to allow light to penetrate further before having to go through a second cell wall, as cell walls absorb or reflect some light
o Rectangular box shapes can be closely packed to form a continuous layer
o Thin cell wall, increasing rate of diffusion of carbon dioxide
o Large vacuole to maintain turgor pressure
Guard cells
o Form small openings called stomata
o Close when loose water by osmosis
o Cell wall is thicker on one side so doesn’t change shape symmetrically as its volume changes
root hair cells
o Root hairs are long projections from cell penetrating between soil particles to reach more water and increases surface area for absorption of minerals and water
vacuole contains cell sap with ions and sugars to lower water pot.
o Present at the surfaces of roots near the growing tips
muscle
o Made of muscle and nerve tissue blood and connective tissue.
o Have skeletal (voluntary), smooth (involuntary), cardiac (in heart).
o Skeletal muscle cells are highly specialised and are multinucleate, and often referred to as muscle fibres, which group together to form a fascicle, and groups of these form muscle.
o The muscle fibres contain the contractile protein myofilaments called actin and myosin which are formed into structures called myofibrils.
