Module 2 Flashcards
light microscope Advantages
• Wide range of specimens can be observed • Specimens can be alive • Specimens can be whole, or embedded in wax ten sectioned
light microscope Disadvantages
• Non-coloured specimens must be stained for specific organelles or molecules • Relatively low resolution does not give detailed information
light microscope Magnification
• Up to 1500x in total
Resolution
• 200nm • Limited by the wavelength of visible light
light microscope Specimen Preparation • into a thin slice
Staining ○ Applying a coloured stain to the sample which binds to certain chemicals/structures, improving their visibility ○ Acetic orcein stains DNA dark red ○ Gentian violet stains bacterial cell walls
Sectioning ○ Specimen is embedded in wax to preserve structure of sample cell walls while cutting them
To correctly use a light microscope
you also need to calibrate the eye piece graticule using the stage micrometer
— this step allows you to measure the size of cells and structures that you are observing.
how to calibrate the eyepiece graticules
To do this, align the stage micrometer (a microscope slide with a scale on it) with the eye piece graticule, then use the reading from the scales to calculate the calibration factor from the objective lens.
Using A Transmission Electron Microscope (TEM)
emits an electron beam through a very thin prepared sample. Electrons penetrate the denser parts of the sample with greater difficulty and this gives the contrast in the 2D image produced.
Using A A Scanning Electron Microscope (SEM)
emits an electron beam directly onto a sample such that none of the electrons penetrate it. Instead, they ‘bounce off’ the sample and are received on asensor, producing a 3D image.
A Scanning Electron Microscope (SEM) Magnification
• SEM: Up to x100, 000
Using A Transmission Electron Microscope (TEM) Magnification
TEM: Up to x500, 000
Resolution (TEM)
• 0.5nm 2000x times more than light microscope • Produces detailed images
resolution SEM)
3-10nm
Magnification
• The degree to which the size of an image is larger than the object itself
Resolution
• The degree to which it is possible to distinguish between two points on an object that are very close together • The higher the resolution, the greater the detail that you can see
Specimen Preparation em
• Specimen needs to be prepared correctly
• Fixed to make it firm
• Dehydrated and embedded in resin
• Stained using metal salts or metal particles
• Mounted on a copper grid
• Placed in a vacuum
• Staining
○ Specimens are stained with metal salts or particles ○ This causes electrons to scatter differently, giving contrast
Advantages
- Produces detailed images of the structures inside cells
* SEM produces detailed 3D images showing contour of cells
Disadvantage
• Electron beams deflected in air, so sample must be in a vacuum • Samples must be dead • Extremely expensive • Large piece of equipment • Use requires a high degree of skill and training
Structure Nucleus
• Largest organelle • Surrounded by nuclear envelope • Contain chromatin • Nucleolus at the centre
Structure Nucleolus •
• Dense spherical structure inside nucleus
Structure Nuclear Envelope
• Surrounds nucleus • 2 membranes with fluid between them • Nuclear pores go through envelope
Structure Rough Endoplasmic Reticulum
• Flattened membrane sacs called cisternae • Continuous with outer nuclear membrane • Studded with ribosomes
Structure Smooth Endoplasmic Reticulum
• Flattened membrane sacs called cisternae • Continuous with outer nuclear membrane • (No ribosomes)
Structure Golgi Apparatus
• Stack of membrane bound, flattened sacs
Structure Ribosomes •
• No outer membrane • Tiny organelles • Each consists of 2 sub-units • Some in cytoplasm, some bound to ER
Structure Mitochondria
• Spherical or sausage shaped • Double membrane • Membranes separated by a fluid filled space • Highly folded inner membrane forms cristae • Central part called matrix
Structure Lysosomes •
• Spherical sacs • Surrounded by single membrane
Structure Chloroplasts •
• Only found in plant cells and some protoctists • Double membrane • Separated by fluid filled space • Continuous inner membrane with elaborate network of flattened membrane sacs called thylakoids • Stack of thylakoids called a granum • Chlorophyll molecules repent on thylakoid membranes and in intergranal membranes
Structure Cell Surface membrane
• Continuous outer membrane • Cell receptors present on surface
Structure Centrioles
• Microtubules • Small tubes of protein fibres • Pair next to nucleus of animal cells
Flagella Structure
• Extension sticking out from cell • Cylinder contains nine microtubules arranged in a circle • Long • Usually present as 1 or 2
Cilia Structure
• Hair-like extensions • Stick out from cell surface • Cylinder contains nine microtubules arranged in a circle • Short • Usually present in large numbers
Function Nucleus
• Houses all of cell’s genetic material • Chromatin consists of DNA and proteins • Has instructions for making proteins
Function Nucleolus
• Makes RNA and ribosomes • These pass into cytoplasm and are the site of protein assembly
FunctionNuclear Envelope
• Pores allow passage of relatively large molecules
FunctionRough Endoplasmic Reticulum
• Transports proteins made on attached ribosomes • Some proteins secreted from cell • Some placed on cell surface membrane
FunctionSmooth Endoplasmic Reticulum
Involved in essential lipid production
FunctionGolgi Apparatus
• Receives proteins from ER and modifies them • Modifies proteins (e.g. Adding sugar) • Packages modifies proteins into vesicles, fro transportation • Some modified proteins are secreted from surface of the cell
FunctionRibosomes
• Site of protein synthesis in the cell • Act as an assembly line where mRNA is used to assemble proteins from amino acids
Function Mitochondria •
site of atp production • Almost all cell activities that require energy are driven by ATP
FunctionLysosomes •
• Contain powerful digestive enzymes • Enzymes break down materials
FunctionChloroplasts •
• Site of photosynthesis in plant cells • Reactions driven by light energy
FunctionCell Surface membrane
• Selectively permeable • Controls exchange between cell and environment • Receptors on cell surface allow for endocytosis and exocytosis
FunctionCentrioles
• Take part in cell division • From spindle fibres, moving chromosomes in cell division
Function Flagella •
• • ‘Tail’ • Enables movement
Cilia Function
x
• ‘Hairs’ • Allow fro movement of substances
Nucleus role in protein synthesis
Contains DNA, which is essentially instructions for the cell to build individual proteins • One gene correlates to one specific protein • Genes are copied into mRNA, which leaves the nucleus via nuclear pores and attaches to a ribosome, which can be found on the rough endoplasmic reticulum (RER). Ribosome
Ribosome role in protein synthesis
‘Reads’ the gene • Accordingly assembles amino acids into a unique sequence • Forms a polypeptide • The polypeptide is pinched off the RER in a vesicle and transported to the Golgi apparatus
Golgi Apparatus role in protein synthesis
• Polypeptide is modified (by joining two or more chains of polypeptides, or adding carbohydrate branches) and… • Packaged into the final protein within a vesicle. • The vesicle is ready to be transported to the cell surface membrane and exocytosed.
cytoskeleton.
network of fibres made from protein
Microtubules
• Cylinders • About 25nm in diameter • Made from Tubulin • May be used to move microorganisms through a liquid, or waft a liquid past a cell • Microtubule motors (proteins) present on microtubules use ATP to move cell contents along the fibres
Actin Filaments
• Move against each other • Cause the movement seen in white blood cells • Move some organelles around within cells
roole of cytoskeleton.
• Provide mechanical strength fro cell • Aids transport within cells ○ Movement of chromosomes during cell division ○ Movement of vesicles from ER to Golgi • Enable cell movement
eukaryotes vs prokaryotes
May have membranes within the cell which form part of encapsulated organelles, e.g. mitochondria and chloroplasts Plant cell wall made out of cellulose; fungal cell wall made out of chitinRibosomes are 25–30nm in diameter DNA stored as chromosomes within the nucleusATP production takes place in mitochondrial cristae (inner membrane folds).Cell diameter 10–100 µm Strictly aerobic only
prokaryotes Only one membrane: cell surface membrane
Cell wall made out of peptidoglycan
Ribosomes are 20nm in diameter
DNA is free in cytoplasm, in the form of a single loop called a ‘circular chromosome’ — as well as some smaller DNA loops called ‘plasmids’.ATP production takes place in the cell surface membraneCell diameter 1–10 µm
Sometimes capable of anaerobic respiration
Water as Solvent
- Any polar molecule ill dissolve in water • Metabolic processes rely on chemicals being able to react together in solutions • Allows cells to maintain concentration gradients
- 70-95% of cytoplasm is water • Important chemical reactions take place here
Water asLiquid
- Transport medium • Freezes at 0°C • Boils at 100°C • Vast majority of water on earth is liquid • Transport of essential materials around organisms and cells
- Blood is an important transport tissue of oxygen, cholesterol and hormones • Around 80% water
Water asCohesion
- Water molecules stick to each other, creating surface tension
- Transport of water in xylem relies in cohesion of water • Some small organisms make use of this and ‘walk’ on water surface
Water asFreezing
- Water freezes forming ice • Ice is less dense than water and floats
- Frozen ice floats to the top, allowing for organism to survive the water beneath
Water asThermal Stability
- Large bodies of water have fairly constant temperatures • Evaporation removes heat energy
- Oceans provide thermally stable environment • Evaporation used as a cooling mechanism
Water asMetabolic
Water is a reactant in important chemical processes • Chemically inert
• Used in hydrolysis and photosynthesis • Very predictable and will not form any unexpected products
Water asMetabolic
Water is a common habitat • Nutrients can be dissolved in water • Water contains oxygen that is essential to life
• Water is an important habitat to many different species of animals • Fish and marine creatures
Cellulose
• Highly abundant in cell walls, making it most common molecule on the planet. • Polymer of about 10,000 β-glucose molecules in a long unbranched chain called a microfibril. • High stability due to structure - several polysaccharide chains running parallel to each other with cross links between them. • The chain cross links are hydrogen bonds and contribute to the strength of the molecule. • Stability renders plants strength and resistance to wind and rain.
use of lipids
energy store, thermal insulator, for buoyancy, and protection of vital organ
Secondary structure
• interaction of individual amino acids which are in the same polypeptide • causes the polypeptide to coil or fold on itself • direct result of hydrogen bonds • results in the polypeptide chain taking one of two forms: ○ B-pleated sheet – Weak – Strength achieved through layering and bonds between layers ○ a-helix – Strong – Helical shape
Tertiary structure
• the way in which an a-helix or B-pleated sheet further coils or folds on itself • forms a more complex 3D shape which often improves its solubility • Due to interactions between R groups and involves: ○ ionic bonds ○ disulphide bonds ○ hydrogen bonds ○ hydrophilic/hydrophobic interactions. • Not all proteins have a tertiary structure • Some polypeptides remain simple long chains, such as keratin or collagen. ○ Such proteins are generally insoluble
Quarternary structure
• interaction between two or more polypeptides • Quaternary structure only exists in proteins consisting therefore of two or more polypeptides • A good example of such a protein is Haemoglobin (Hb) (shown in diagram) ○ bHb ecomes a biologically active molecule upon the establishment of its quaternary structure ○ Hbhas 4 sub-chains and its role is to carry iron and oxygen around the body ○ Has a globular quaternary structure • Another example is collagen ○ has a fibrous quaternary structure
globular
- Roll up to form balls
- Any hydrophobic R groups turn inwards • Any hydrophilic R groups turn outward • This makes these proteins water soluble
- Usually have metabolic roles
- Enzymes (e.g. lactase) • Plasma proteins • Antibodies • Some hormones (e.g. insulin) • Haemoglobin
Fibrous •
- Form fibers • Regular, repetitive sequence of amino acids
- Usually insoluble • Usually have structural roles
- Collagen • Keratin
Haemoglobin
Globular Soluble Range of amino acids present in primary structure Prosthetic haem group Majority is wound into alpha helix structures • 2 a-chains • 2 B-chains
collagen
Fibrous Insoluble No prosthetic group
Majority is left-handed helix structures
Biuret test for proteins
The biuret test enables us to test a sample for the presence of protein. 1. Biuret reagent (composed of copper sulphate and potassium hydroxide) is normally blue 2. The reagent turns purple in the presence of peptide bonds, indicating presence of protein
Benedict’s test for reducing and non-reducing sugars
All monosaccharides are reducing sugars, while disaccharides can be either reducing or nonreducing. 1. Benedict’s reagent is composed of copper-II sulphate in alkaline solution 2. Add the reagent to the sample and heat in a water bath (80°C) for 3 minutes 3. In the presence of a reducing sugar, Cu2+ ions are reduced to Cu+ and the sugar is oxidised 4. Colour changes to red 5. If no colour change present, this could indicate either: a. Absence of any sugar b. Presence of non-reducing sugar
To check whether a non-reducing sugar is present
we first need to break down the sugar into its reducing sub-parts. For instance, sucrose needs to be broken down into glucose and fructose before it will react with Benedict’s reagent. We can achieve this by: 1. Heat solution with acid to hydrolyse any glycosidic bonds present 2. Neutralise solution with sodium hydroxide 3. Add benedict’s reagent and heat in water bath for 3 minutes 4. If colour changes to orange/red then a non-reducing sugar was originally present
Iodine test for starch
- Use potassium iodide solution as source of iodine 2. In the presence of starch, the solution will turn a dark blue-black colour 3. This is due to iodine becoming trapped inside the coils of starch
Emulsion test for lipids
- Shake sample with ethanol 2. Pour solution into water 3. If the mixture turns cloudy, lipids are present 4. This is due to lipids’ solubility in ethanol and insolubility in water
Stationary Phase
• Can be cellulose chromatography paper or • Thin-layer chromatography (TLC) plate
Mobile Phase
• Solvent for molecules to be identified • Use water for polar molecules • Use ethanol for non-polar molecules
steps of tlc
- Prepare a beaker with a small amount of solvent (mobile phase) 2. Draw a line along the bottom of the chromatography paper piece a. Draw in pencil b. The line should high enough on the strip to not be submerged in solvent when placed in the beaker 3. Draw a tiny dot on the line to mark where you will apply your sample 4. Place the paper in the beaker 5. Cover the beaker with a glass plate 6. Leave the apparatus until the solvent has been absorbed by the paper and travelled to the other end of it 7. Use where a. x = distance travelled by each solute and b. y = distance travelled by the solvent 8. Each biological molecule has its own Rf and is thereby identifiable
Fuctions of DNA
Acts as an information store • Bases projecting from backbone act as a coded sequence • Organisms differ in their DNA only because they contain different sequences of bases in DNA • Contains ‘information’ to inform the primary structure of a protein Needs to be replicable • Produce copies that preserve the base sequences • Preserve information • Base-pairing rules allow for this Long molecule • Lots of information can be stored • Double helix provides stability
Structure
• Deoxyribonucleic Acid • Stable Polynucleotide ○ long-chain polymer of nucleotide monomers • Usually double stranded
Base Pairing
• DNA strands run parallel to each other • Bases project inwards, running in opposite directions (‘anti-parallel’) • Chains always the same distance apart as bases pair in a specific way ○ A-T ○ G-C • When a purine appears on one side, a pyridimine appears on the other • As the strands come together, hydrogen bonds form between the base pairs • Differing structure of the bases, means that base pairing rules always apply • This form of pairing is described as complementary ○ A is complementary to T ○ G is complementary to C • The 2 strands twist to form double helix of final structure • Held together by hydrogen bonds which are strong enough to maintain DNA structure but weak enough to be overcome during DNA replication
DNA replication
• ensures the preservation of genetic information stored in DNA • Important as the structure and functions of proteins coded according to DNA relies entirely upon the correct sequences being copied • Some mutations occur very infrequently and randomly • These might not result in a phenotypic change, but sometimes can have life-altering consequences
Semi-Conservative DNA Replication
- DNA double helix unwinds and “unzips”; the hydrogen bonds between base pairs are broken. This process is brought about by an enzyme called DNA helicase. 2. The exposed nucleotide bases act as a template for assembly of the new DNA strand. 3. Free nucleotides move towards these exposed bases according to the base pair rule. 4. An enzyme called DNA polymerase binds the nucleotides together with covalent bonds, forming the new sugar-phosphate backbone.
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transcription
Transcription = the process of copying RNA from DNA 1. DNA strand unwinds and unzips by DNA helicase 2. Instead of a new DNA strand being formed, RNA nucleotide bases pair up with the exposed DNA bases 3. An enzyme called RNA synthase forms covalent bonds between the nucleotide bases 4. Unlike DNA, RNA is single-stranded 5. A messenger RNA (mRNA) strand is formed and breaks away from the DNA which then rezips itself up thanks to the natural formation of hydrogen bonds 6. mRNA is now free to migrate out of the nucleus through nuclear pores
Translation
= the process of creating polypeptides based off mRNA 1. Once mRNA has left the nucleus, it attaches to a ribosome on the rough endoplasmic reticulum 2. Transfer RNA (tRNA) carries the corresponding amino acid to each on the mRNA 3. The anti-codon is a triplet of bases that form part of a tRNA molecule and ensure that the correct amino acid is joined onto the polypeptide chain 4. This process is active and requires ATP 5. The amino acid transported by the tRNA attaches to the ribosome 6. Adjacent amino acids join together by peptide bonds, creating a polypeptide chain 7. This process continues until the ribosome reaches a ‘stop’ codon (triplet) on the mRNA. At this point, the polypeptide breaks loose from the ribosome and is free.
Lock and Key Hypothesis •
Every enzyme has an active site which binds to a substrate • The enzyme’s active site is formed by its tertiary structure and is specific to the substrate • It will have no effect on a molecule that comes into contact with its active site but doesn’t relate to the enzyme’s function • The idea of active site specificity is called Lock and Key theory, because the active site acts like a lock and the substrate acts like a key.
Induced Fit Hypothesis
• The enzyme’s active site is not perfectly matched to the substrate before the two bind to form the enzyme-substrate complex
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• When the complex is formed, the tertiary structure of the enzyme changes slightly • It is this change in shape that enables the reaction to happen at a lower activation energy.
Effect of pH on enzyme activity •
The tertiary structure of an enzyme relies on hydrogen bonding. • Each enzyme has a tertiary structure that is optimal for most efficient action • changes in pH from the enzyme’s optimal pH change hydrogen bonding in tertiary structure • Enzymes are built to work optimally at the pH of their natural environment ○ e.g. trypsin, which works in the stomach, works best at low pH ○ arginase is often in the presence of ammonia which is alkaline, and this enzyme has a higher ‘optimal pH’.
Effect
Effect of temperature on enzyme activity •
Small increase in temperature can increase enzyme activity as the kinetic energy of the enzyme and the substrate increase. • They are therefore more likely to come into contact with each other. • They also collide with greater force • Therefore are more likely to form an enzyme-substrate complex when they do meet. • As temperature increases, it will approach the enzyme’s optimal temperature: where the enzyme is working at maximum efficiency. • Beyond this temperature, the enzyme becomes denatured. • Bonds responsible for maintaining the enzyme’s tertiary structure become broken and the active site changes shape • Enzyme becomes totally inefficient
Effect of enzyme concentration on enzyme activity
• Rate of reaction and enzyme concentration are directly proportional, ○ provided substrate molecules are in excess and enzyme availability is the only limiting factor. • Where substrate is in limited supply, as it all becomes reacted, less and less becomes available, so the rate of reaction curves off.
Effect of substrate concentration on enzyme activity
The rate of reaction and substrate concentration are directly proportional, up to a given point. • This point is called Vmax, • At Vmax, all the enzyme active sites are said to be ‘saturated’ or occupied. • There are no available active sites free to bind with substrates. • At Vmax, the amount of enzyme becomes the limiting factor.
Cofactor
= non-protein component of an enzyme that is required in order for the enzyme to function. • E.g. Cl – is a co-factor for amylase
Coenzyme
= organic, non-protein molecule whose role is to transport chemical groups between enzymes, linking together controlled enzyme reactions. • E.g. Vitamins are a diverse group of coenzymes • NADP is a coenzyme to photosynthesis • NAD and FAD are coenzymes in respiration
Prosthetic group
coenzyme that is a permanent part of the enzyme • E.g. Zn2+ is a prosthetic group in carbonic anhydrase
Competitive
• Can fit into the active site, but does not react • Competes with substrate for access to the active site • Effect is concentration dependent • Can be minimized by raising the concentration of substrate • Effects are reversible
Non-competitive
• Binds to allosteric site • Changes the shape of the molecule, preventing it from working • This is permanent and cannot be rectified • Effect is independent of substrate concentration
Reversible inhibitors
• Bind reversibly to the enzyme • Have no long-lasting effect since they detach themselves after a while
Irreversible inhibitors
• Binds irreversibly • Even if in high competition with substrate, can eventually inhibit a large proportion of available enzyme
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• Can have long-lasting effects • Until organism generates more enzyme and the inhibitor is outnumbered by enzyme • E.g. aspirin
metabolic inhibitors
Some poisons act as metabolic inhibitors. For example, potassium cyanide is a non-competitive inhibitor to the enzyme cytochrome oxidase. The effect of this poison is to decrease the body’s ability to respire using oxygen, so it begins to respire anaerobically, causing lactic acid accumulation in the blood
Role of Membranes
- To act as partially (and sometimes selectively) permeable membranes between: ○ A cell and its environment ○ An organelle and the cytoplasm which surrounds it ○ Within organelles (e.g. mitochondria/chloroplasts) 2. Sites of chemical reactions 3. Sites of cell communication and signalling
‘fluid mosaic model’
that the membrane is constructed from several different components including phospholipids, proteins, and modified proteins, and that these membrane constituents (phospholipids and are continually moving relative to each other, i.e. not fixed.
• Phospholipids
which form the bilayer and the bulk of the membrane surface area
Cholesterol,
which regulate membrane mobility and flexibility
Proteins,
which are involved in more complex functions such as carrying out chemical reactions or regulating cross-plasma transport ○ Can be intrinsic/integral (span the entire membrane) ○ Can be extrinsic (embedded in one half of the membrane) ○ Can form cross-membrane channels
• Glycoproteins and glycolipids,
which can be antigens or receptor molecules
high temperature effect on the structure or permeability of a membrane.
can denature some of the components of the membrane, such as the proteins and glycoproteins, changing their effect and reducing their ability to control transport of molecules across the membrane. Therefore, at high temperatures, the membrane becomes denatured and more permeable.
ph effect on the structure or permeability of a membrane.
pH has a similar effect, by denaturing the proteins in the membranes that are in pH other than the optimal pH for that cell or organelle.
Diffusion
• Movement of molecules or ions from an area of high concentration to an area of lower concentration • Until the concentrations of the two regions are equal • Dynamic equilibrium established • Passive process • The rate of diffusion is proportional to the concentration gradient the distance over which the diffusion must occur • Substances capable of diffusion across the cell surface membrane include ○ Oxygen ○ carbon dioxide ○ Steroids ○ the fat-soluble vitamins (A,D,E,K) ○ Glycerol ○ alcohols and ○ ammonia.
Osmosis
• Specialised form of diffusion • Diffusion of water molecules from an area of high water potential (high concentration) to an area of low water potential (low concentration) • Through a partially permeable membrane • Passive process
Facilitated diffusion •
Faster than normal diffusion • Used to transport molecules such as ○ Glucose ○ Fructose ○ non fat-soluble vitamins ○ urea and ○ many ions across the membrane. • Occurs down the concentration gradient • Passive process
• There are four key steps involved in facilitated diffusion
○ Glucose binds with transport protein molecules on the cell surface. Different cells have different types of glucose transporter. ○ The transport protein changes shape. ○ The glucose is transported through the membrane to the inside of the cell. ○ The glucose detaches from the transporter protein and the protein reverts to its original shape. The glucose is then immediately phosphorylated, so the concentration of glucose inside the cell remains low and the concentration gradient across the membrane is maintained
Active Transport
Ions such as ○ sodium (Na+) ○ potassium (K+) ○ chloride (Cl-) ○ hydrogen (H+) and ○ molecules such as amino acids and glucose require active transport across the cell surface membrane • ATP is required • Active process • This is because the movement of these ions/molecules is against the concentration gradient • All of these substances can cross the membrane by facilitated diffusion if the concentration gradient is the right way round and if transporter channels are available. • Commonly involves a protein which acts as a Na+/K+ pump.
The
Animal cell Hypotonic
• Water potential outside cell higher than inside • Water moves in by osmosis • Cell swells may burst • (Haemolysis)
Animal cell Isotonic
• Water potential both inside and outside are equal Water flows in and out at an equal rate
Animal cell Hypertonic
• Water potential outside cell lower than inside • Water moves out of the cell by osmosis • Cell shrinks • (Crentation
Plant cellHypotonic
• Solution has higher water potential than vacuole • Water flows in by osmosis • Cell swells, becomes turgid • Cannot burst because of cell wall
Plant cell Isotonic
• Neither turgid nor plasmolysed • Water moving in and out at same rate
Plant cell Hypertonic
• Solution has lower water potential that vacuole • Water flows out by osmosis • Cell shrinks, becomes plasmolysed • Cell wall rigid and does not collapse
G0 , G1
• Biosynthesis • Growth phase • Biosynthetic activities resume at a high rate • Amino acids used to form millions of proteins • Proteins required in DNA replication • Chromosomes still exist as chromatin • DNA replication has not yet occurred
S
• Synthesis of new DNA • DNA replication begins • When completed, all chromosomes are replicated • Occurs very quickly
G2
• Cell continues to grow • Proof-reading enzymes check the DNA • Check to see if the chromosomes have been replicated properly
M
• Nuclear division • The process of mitosis is carried out
Copying and Separating
• Molecules of DNA wrapped around proteins called histones ○ Allows DNA to be highly condenses ○ Compact and condensed DNA is able to fit inside the nucleus • DNA and histone protein together are called chromatin ○ Chromatin thread about 30nm thick • Before cell division, DNA of each chromosome must be replicated ○ 2 replicas produced, both exact copies of the original ○ Held together at the centromere
why cell regulation
To avoid abnormal cell activity that can lead to, for example, tumour growth, the cell cycle has three checkpoints to regulate itself.
• G2 checkpoint
• ○ Checks for cell size and DNA replication
M checkpoint
○ Checks that chromosomes appropriately attached to spindle
G1 checkpoint
○ Checks cell size, nutrient availability, growth factor availability and confirms intact DNA
Interphase
• DNA replication • Organelle doubling • Proteins made • Cell ‘double checks’ for mutations
Prophase
• Replicated chromosomes super coil (shorten and thicken) • Chromosomes already replicated in Interphase • Chromosomes shorten and thicken • Pair of sister chromatids can be seen using a light microscope • Nuclear envelope breaks down and disappears • Centrioles divides in 2, forming 2 daughter centrioles ○ Each daughter centrioles moves to opposite ends of cell • This forms the spindle • This is ‘threads’ of protein (look like latitude lines on a globe) • Nuclear membrane breaks down
Metaphase
• Replicated chromosomes line up down middle of ell • Move to central region of spindle • Each becomes to spindle thread by its centromere
Anaphase
• Replicas of each chromosome pulled apart • Towards opposite ends of the cell • Sister chromatids separated as centromere splits • Each sister chromosomes effectively become individual chromosomes • Each one genetically identical to the parent cell from which it was copied • Spindle fibers shorten • This pulls sister chromatids further and further away from each other • Form a v-shape as spindle fibers, joined to the centromere, lead
Telophase
• Two nuclei formed • As each sister chromatids reaches the pole of the cells, new nuclear envelope forms around each set • Spindle breaks down and disappears • Chromosomes uncoil • Can no longer be seen under a light microscope
Cytokinesis
• Cytoplasm and surface membrane divide
Animal Cells
Capable of mitosis and cytokinesis • Cytokinesis starts from outside (‘nipping’ in the cell)
Plant Cells
• Only meristem cells can divide this way • Do not have centrioles • Tubulin protein threads made in cytoplasm • Cytokinesis starts with the formation of a new cell plate where spindle ‘equator’ was • New cell membrane and wall laid down along this plate
Animal Cells and mitosis and cytokinesis
Capable of mitosis and cytokinesis • Cytokinesis starts from outside (‘nipping’ in the cell)
Plant Cells and mitosis and cytokinesis
• Only meristem cells can divide this way • Do not have centrioles • Tubulin protein threads made in cytoplasm • Cytokinesis starts with the formation of a new cell plate where spindle ‘equator’ was • New cell membrane and wall laid down along this plate
why mitosis
• All organisms need to produce genetically identical daughter cells • Mitosis is incredibly significant in many different settings
Asexual Reproduction • Single-celled organisms divide to produce 2 daughter cells, that are separate organisms • E.g. Paramecium • Some multicellular organisms can produce offspring from parts of the parent plant • E.g. Hydra
Growth • Multi-cellular organisms grow by producing new cells • Each new cell is genetically identical to parent cell
Repair • Damaged cells need to be replaced • New cells need to perform the same function – so need to be identical
Replacement • Red blood cells and skin cells are regularly replaced by new cells
The Significance of Meiosis in Life Cycles
Importance • Takes place in sex organs • Gametes produced here • Important to have genetically different gametes • This promotes genetic variation and allows for Natural Selection to take place.
Importance • Takes place in sex organs • Gametes produced here • Important to have genetically different gametes • This promotes genetic variation and allows for Natural Selection to take place
Meiosis
is the process of cell division which produced four daughter cells which are not identical - they are different from each other. They have half the number of chromosomes as the parent cell, making them haploid. The process involves 2 nuclear divisions.
recombination
during prophase I, recombination occurs. This is what creates genetic diversity and involves chromatids swapping genes between themselves. Recombination ensures that the four daughter cells are not genetically identical.
Prophase II
• Chromosomes pair up • Pair of sister chromatids can be seen using a light microscope • Centrioles divides in 2, forming 2 daughter centrioles • Nuclear membrane breaks down
Metaphase II
• Replicated chromosomes line up down middle of cell • Centrioles move to opposite poles of the cell, forming spindle • Chromosomes move to central region of spindle • Each becomes to spindle thread by its centromere
Anaphase II
• Sister chromosomes pulled apart towards opposite ends of the cell • Sister chromatids separated as centromere splits • Each sister chromosomes effectively become individual chromosomes • Each one genetically unique • Spindle fibers shorten • This pulls sister chromatids further and further away from each other
Telophase II
• New nuclear envelope forms around each chromatid • Spindle breaks down and disappears • Chromatids uncoil and can no longer be seen under a light microscope
Cytokinesis II
• Cytoplasm and surface membrane divide, creating four independent haploid daughter cells.
specialised Erythrocytes •
• Come from undifferentiated stem cells in bone marrow • Cells lose all organelles • Bi-concave shape • Maximizes oxygen carrying capacity • Maximizes space for haemoglobin
specialised Neutrophils
• Lobed nucleus • Granular cytoplasm contain lots of lysosomes • Potent enzymes in lysosomes specialized to kill microorganisms
specialised Epithelial Cells
• Cover external and internal surfaces • 2 types ○ Squamous cells ○ Ciliated cells
specialised Sperm Cells •
• Many mitochondria generate energy for movement • Sperm head contain specialized lysosomes to break down wall of egg • Small, long and thin to ease movement • Tail helps to propel the sperm • Diploid, in order to fulfill role as gamete
specialised Palisade Cells
• Long shape maximizes light absorption • Contain large amounts of chlorophyll • Specialized for photosynthesis
specialised Root Hair Cell
• Hair like projections • Greatly increase surface area • Root able to absorb more water and minerals from soil
specialised Guard Cells
• Spiral thickenings of cellulose • When turgid, cell opens • When flaccid, stoma closes • Controlling passage of gases
Tissue =
a group of similar, specialised cells in a multicellular organism, which collectively are able to carry out a specific or several specific functions
Organ =
group of tissues combined to form a distinct structure and which collectively might carry out a specific function which has an effect on the entire organism, e.g lungs, liver, heart
Organ system =
collection of organs with related and interdependent functions, e.g. cardiovascular and digestive systems.
Squamous epithelia
• Found in lining of oral cavities, blood vessels, alveoli of lung, skin epithelium, and other places • Some variants of squamous epithelium are thin and lubricated to enable efficient gas exchange, e.g. in lung • Others are reinforced with keratin to improve resistance to friction and infection, e.g. the skin
Ciliated epithelium
Found in upper airway tract (trachea) and fallopian tubes • Cells constituting this type of epithelium are specialised with large number of cilia • They are able to waft material in a single direction, e.g. pathogens and mucus away from the lungs and towards the oral cavity, or ova away from the ovary and towards the uterus
Cartilage
• Cells in cartilage are specialised to resist pressure and provide lubrication for joint movement • Muscle • Cells in muscle (myocytes) can store and convert large amounts of energy • Phloem • Transports glucose and some other compounds up and down the plant stem - is highly specialised to ensure efficient movement of sugar to areas of the plant that need it most
Xylem
• transports water up the stem of a plant • Highly specialised to transport water against the direction of the force of gravity
Multipotent
Forms cells of tissue in which they were formed
Omnipotent
only forms one type of tissue
Pluripotent
can develop into every cell in the bodty
Erythrocytes
• Red blood cells • Cell loose nucleus, mitochondria, Golgi apparatus and rough E.R • Packed full of hemoglobin • Shape changes, forming biconcave discs • This allows them to transport oxygen
Neutrophils
• A type of white blood cell • Keep nucleus • Cytoplasm appears granular • Large number of lysosomes produced • This aids their role of ingesting invading microorganisms
In plants, stem cells are found in …
the growing tip and the cambium. They are produced from meristem cells in the meristem, and also found in roots.
The Potential of Stem Cells in Research & Medicine
Bone marrow transplants • Already widely used • Bone marrow is major source of stem cells - especially stem cells capable of becoming blood cells ○ E.g. red blood cells and white blood cells • Used therapeutically to treat blood and immune disorders
Drug research • In theory, stem cells can be used to grow artificial tissues • Drugs can then be tested on these tissues before being tested on human subjects
Developmental biology • Stem cells provide insight into embryological development • Important information about how our organs are formed • Can explain why they fail, or have abnormalities • This information can be used to improve medicine
Replacement of lost or damaged tissues • The dream’ of stem cell research • Mice have been treated for Type 1 diabetes mellitus with artificial pancreatic cells which secrete insulin normally • Stem cells could also be used to grow into specific organs or even limbs • They have the potential to treat many conditions
