3 - biologypost
[pic]
AQA
AS Biology
Unit 1:
‘Biology & Disease’
Summary Notes
Biochemistry
Organisation of matter
• Matter: anything that occupies space and has mass.
• All forms of matter are made up of elements.
• The elements hydrogen, carbon and oxygen make up most of the human body.
• Atoms: the smallest unit of matter that are unique to a particular element.
• Molecules: units of two or more atoms bonded together.
• Protons: positive particles.
• Neutrons: neutral particles.
• Electrons: negative particles.
Bonding
Ionic bonding:
• An association between 2 oppositely charged ions.
• Charged particles (ions) have a change in the number of their electrons.
• Negative ions gain electrons.
• Positive ions lose electrons.
Covalent bonding:
• Atoms share electrons.
• Single bond – 1 pair shared, eg H2.
• Double bond – 2 pairs shared, eg O2.
• Triple bond – 3 pairs shared, eg N2.
• Polarity: Some covalent molecules are polar.
o Atoms of different elements do not exert the same pull.
o The net charge is balanced.
o Eg. water.
Hydrogen bonding:
• ‘Van Der Waal’s forces’.
• An atom of a molecule interacts with another hydrogen atom that is already taking part in a covalent bond.
• Due to polarity – the overall charge of each molecule is neutral, but the distribution of electrons is uneven.
• Individually weak.
• Collectively stabilising.
[pic]
• Examples:
o Between water molecules.
o Between water and ammonia.
o Between water and glucose.
o Within DNA – base pairing.
Polymers and Monomers
Biological molecules such as carbohydrates and proteins are often polymers and are based on a small number of chemical elements.
|Group Name |Polymers |Polymer example |Monomers |Monomer example |
|Carbohydrates |Polysaccharides |Starch |Monosaccharides |α-glucose |
|Proteins |Polypeptides |Amylase |Amino acids |Leucine |
|Nucleic acids |Polynucleotides |DNA |Nucleotides |Adenosine phosphate |
Carbohydrates
General details:
• Hydrates of carbon.
• Contain carbon, hydrogen and oxygen.
• General formula Cx(H2O)y.
• 3 groups:
o Monosaccharides – single sugars.
o Disaccharides – double sugars.
o Polysaccharides – many sugars (more than 2).
• Uses:
o Structural – cellulose, chitin.
o Energy – glucose.
o Storage – glycogen, starch.
o In nucleic acids – ribose, deoxyribose.
Monosaccharides
• The basic molecular units (monomers) of which carbohydrates are composed.
• General formula CH2On
• Glucose - C6H12O6.
• Hexose sugar.
• Main substrate for respiration.
• Transported in mammalian blood.
• Monomer for starch, glycogen and cellulose.
• The structure of α-glucose:
[pic]
• α-glucose link together by glycosidic bonds
• This is a condensation reaction - Involves the loss of a water molecule.
• It joins 2 sugars by an oxygen.
[pic]
• Hydrolysis reaction – required to split the glycosidic bond.
• This requires the use of a water molecule to reform the hydroxyl groups on each of the two new sugars where the bond is split.
Disaccharides
• Maltose is formed by condensation of two α-glucose molecules
• Maltose has an α 1,4 glycosidic bond – between carbons 1 and 4.
• Maltose is a reducing sugar.
• Sucrose is formed by condensation of glucose and fructose.
• Sucrose is a non-reducing sugar.
• Lactose is formed by condensation of glucose and galactose.
• Lactose is a reducing sugar.
Polysaccharides
• Polysaccharide = ‘many sugars’.
• Polymers of monosaccharides.
• Formed by condensation reactions.
• Variable numbers of monosaccharides.
• Branched or unbranched chains.
• May be folded.
• Insoluble due to size.
• Exert no osmotic influence.
• Do not diffuse easily.
• Split into disaccharides and monosaccharides by hydrolysis.
Starch
• Found in most parts of a plant in starch grains.
• Food reserve from excess glucose.
• Food supply in seeds for germination.
• Important food supply in animals.
• Made of α glucose.
• Compact for storage.
• 2 constituent structures:
o Amylose:
▪ Approx 20% of starch.
▪ α 1,4 glycosidic bonds.
▪ Spiral structure held together by hydrogen bonds.
o Amylopectin:
▪ Approx 80& of starch.
▪ α 1,4 and α 1,6 bonds.
▪ Branched chains.
[pic]
Proteins
• Polymers of amino acids.
• Large molecular mass.
• Wide variety of functions.
• Carbon, hydrogen, oxygen and nitrogen.
• Usually sulphur as well.
• Each species has a particular range of proteins.
• Determined by the genetic code.
• Make up two-thirds of total dry mass of cell
• Make up 18% of human body (second only to water)
• Most complex and diverse group of biological compounds
Range of Functions:
|Function |Examples |
|Structure |Collagen (bone, cartilage, tendon), Keratin (hair) Actin (muscle) |
|Enzymes |Amylase, pepsin, catalase |
|Transport |Haemoglobin (oxygen) |
|Active transport |Sodium – Potassium pumps in cell membranes |
|Muscles |Myosin and actin |
|Hormones |Insulin, glucagon |
|Antibodies |Immunoglobulins |
Amino Acids
• Proteins are made up of amino acid chains.
• The general structure of an amino acid is:
R
I
H2N – C – COOH
I
H
• The central carbon has 4 groups attached to it:
o a hydrogen atom
o a basic amino group
o an acidic carboxyl group
o a variable ‘R’ group (or side chain)
• There are 20 naturally occurring amino acids in living organisms.
• Half of these can be created in the body – non-essential amino acids.
• The other half must be consume in the diet – essential amino acids.
Peptide Bond
• When 2 amino acids join together they form a dipeptide using a peptide bond or link.
• This is a condensation reaction.
[pic]
• To break this bond requires a hydrolysis reaction.
• This requires the use of a water molecule to reform the amino and caboxyl groups on each of the two new amino acids where the bond is split.
Polypeptides
• Many amino acids make up a polypeptide chain.
• Amino acid polymerisation for polypeptides is part of protein synthesis.
• The sequence of amino acids in a chain is determined by the sequence of the genetic code in DNA.
Protein structure
Protein structure can be broken down into 4 levels:
Primary structure
• The primary structure refers to the sequence of amino acids
• Determines rest of protein structure
Secondary structure
• Amino acid chains fold and move to take up a particular shape
• Amino acids find the most stable hydrogen bonds
• Most common secondary structures are α-helix and the β-sheet
Alpha –helix:
• A regular spiral
• Held together by hydrogen bonds
• Very stable
• Forms part of most proteins
Beta-pleated sheet:
• A zig-zag formation
• Consisting of two or more chains
• Running parallel to each other
• Linked by hydrogen bonds.
[pic]
Tertiary structure
• Overall three-dimensional shape formed by the folding up of a whole polypeptide chain.
• Every protein has a unique tertiary structure, which is responsible for its properties and function.
• Tertiary structure held together by bonds between the R groups of the amino acids. There are 3 different types:
o hydrogen bonds – weak
o ionic bonds – between oppositely charged R groups, quite strong
o disulphide bridges – strong covalent bonds between sulphur on cysteine R groups.
Quarternary structure
• Final three-dimensional structure
• This is how different polypeptide chains are joined together.
• Also includes non-protein prosthetic groups which are present in some proteins.
• Eg, haemoglobin is a globular protein with 4 polypeptide chains, each with a haem group (containing an atom of iron).
Fibrous proteins:
• Long supercoiled chains.
• Secondary structure is important.
• Many polypeptide chains run parallel, cross-linked with bonds, eg disulphide bridges.
• Stable, and structurally strong.
• Examples:
o Keratin – skin, hair, bones.
o Collagen – skin, bones and tendons.
o Fibrin – blood clots
Globular Proteins:
• More spherical.
• Smaller ones are soluble.
• Specific shape.
• Tertiary and quaternary structure forms specific shape.
• Often part of the protein has a complementary shape to another specific molecule.
• Examples:
o Hormones – eg insulin and glucagon attach to receptors on cell membranes
o Enzymes – active site specific to substrate
o Antibodies – complementary to specific antigens
o Haemoglobin
Lipids
General details:
• Large, varied group of organic compounds.
• Contain carbon, hydrogen and oxygen.
• Insoluble in water.
• Dissolve in organic solvents, eg alcohol.
• 3 main types:
o Triglycerides.
o Phospholipids.
o Steroids.
The molecule
• 2 main sections:
[pic]
o Glycerol:
• An alcohol containing 3 carbon atoms.
• Each carbon has a hydroxyl group.
o Fatty acids:
• These determine the characterisitics of the lipid.
• They contain a carboxyl group (-COOH).
• This is attached to a variable R group - a hydrocarbon chain.
• 2 groups of fatty acids:
• Saturated:
o No double bonds between carbon atoms.
o Eg butyric acid found in butter.
o Eg palmitic acid found in animal and vegetable fats.
o A high proportion in the diet may increase risk of heart disease.
• Unsaturated:
o On or more double bonds,
o Eg linoleic acid – linseed oil.
o Eg oleic acid – found in olive oil.
o Polyunusaturated have 2 or more.
o Monounsaturated have one.
[pic]
Bonding:
• Fatty acids bond to glycerol by an ester linkage.
• Formation is a condensation reaction.
• Hydrolysis reactions break the bond.
• An oxygen atom joins a carbon on the glycerol with carbon on the carboxyl end of the fatty acid.
Triglycerides
• 3 fatty acid chains.
• Differ according to type and length of chains.
o Oils:
▪ Relatively short fatty acids or unsaturated fatty acids.
▪ Tend to be liquid at room temperature.
o Fats:
▪ Longer fatty acid chains or saturated fatty acids.
▪ More likely to be solid at room temperature.
▪ Main use is as an energy source.
▪ Can be broken down into glucose (gluconeogenesis) and used in respiration.
Uses:
• Animal energy stores.
• Twice as much energy per gram as carbohydrates.
• Ideal for the low mass required for locomotion.
• Insulation:
• Conduct heat slowly.
• Protection of vital organs.
• Waterproofing fur and feathers with oil secretions.
Phospholipids
• One fatty acid group is replaced by a phosphate group.
• The fatty acid chains are hydrophobic.
• The phosphate group and glycerol part are hydrophilic.
• Main role is in cell membranes.
[pic]
Microscopes
Units of measure
1 meter = 1,000 mm = 1,000,000 µm = 1,000,000,000 nm
1 millimeter (mm) = 1/1000 m
1 micrometer (µm) = 1/1,000,000 m = 1/1000 mm
1 nanometer (nm) = 1/1,000,000,000 m = 1/1000,000 mm = 1/1000 µm
Examples:
Frog egg = 1mm
Human egg = 100 µm
Most animal cell = 10 to 30 µm
Most plant cells = 10 to 100 µm
Prokaryotic cells = 1 µm
Mitochondria = 0.5 to 1 µm
Chloroplast = 5 µm
Nucleus = 7 µm
Virus = 10 to 300 nm
Ribosome = 30 nm
Magnification:
• The ratio of how much bigger a sample appears when viewed under the microscope than its actual size.
• The resolution limits how much detail can be seen.
Calculating magnification from photographs:
Magnification = length in photograph
Real length
Calculating real length from photographs:
Real length = Length in photograph
Magnification
NB for both, convert the length in the photograph into the same units that are used for the specimen. This is usually in micrometers.
Resolution
• The smallest separation at which two separate objects can be distinguished (or resolved).
• The greater the resolving power, the more detail can be seen.
• The resolution of an image is limited by the wavelength of radiation used to view the sample.
• When objects in the specimen are smaller than the wavelength of the radiation being used, they do not interrupt the waves, and so are not detected.
• The resolving power of a light microscope is limited by the wavelength of light (400-600nm for visible light).
• Objects closer than 200nm will still only be seen as one point, no matter how great the magnification.
• Electrons have a much lower wavelength than light.
• A beam of electrons has an effective wavelength of less than 1 nm.
• Electron microscopes have higher resolution.
Light Microscopy
[pic]
• Most widely used form of microscopy.
• Specimens are illuminated with light
• Focussed using glass lenses.
• Modern microscopes - Compound microscopes use several lenses to obtain high magnification.
• Light microscopy has a resolution of about 200 nm:
• View cells, and large organelles but not the details of organelles
• Specimens can be living or dead.
• Specimens often need to be stained with a coloured dye to make them visible.
• Many different stains are available that stain specific parts of the cell such as DNA, lipids, cytoskeleton, etc.
Electron Microscopy.
• Developed in 1930s.
• Uses a beam of electrons to "illuminate" the specimen.
• Electrons behave like waves.
• Produced using a hot wire
• Focussed using electromagnets
• Detected using a phosphor screen or photographic film
• A beam of electrons has an effective wavelength of less than 1 nm.
• Resolving power is enough to view small sub-cellular ultrastructure.
• Mitochondria, ER and membranes can be seen in detail.
Problems
• Specimens must be fixed in plastic or covered in heavy metals.
• Viewed in a vacuum.
• Therefore, specimens must be dead.
• The electron beam can damage specimens.
• Must be stained with an electron-dense chemical, usually heavy metals like osmium, lead or gold.
• People argue that many observed structures could be artefacts - due to the preparation process and not real.
Transmission electron microscope (TEM)
[pic]
• Works much like a light microscope.
• A beam of electrons is passed through a thin specimen.
• Electrons are focussed to form an image on a fluorescent screen or on film.
• Most common form of electron microscope.
• Best resolution – 0.2 nm
• Creates a 2-dimensional flat image.
The scanning electron microscope (SEM)
[pic]
• A fine beam of electron is scanned onto a specimen.
• Electrons are scattered by the surface, due to the heavy metal covering.
• A fluorescent screen or film is used to detect the reflected electrons.
• This has poorer resolution – 10 nm
• Gives 3-dimentional images of surfaces.
• The electrons do not have to pass through the sample in order to form the image.
• Larger, thicker structures can be seen under the SEM.
Separating Cell Components
Cell Fractionation
• The separation of different parts and organelles of a cell.
• Relative proportions of each organelle can be discovered.
• Biochemical contents of each organelle can be investigated.
Process:
1. Place tissue (e.g. liver, heart, leaf, etc) in ice-cold isotonic buffer.
• Cold to stop enzyme reactions.
• Isotonic to stop osmosis.
• Buffer to stop pH changes.
2. Grind tissue in a blender to break open cells –homogenation.
3. Filter to remove insoluble tissue e.g. fat, connective tissue, plant cell walls, etc. This filtrate is now called a cell-free extract.
Differential Centrifugation
• A centrifuge is a piece of equipment, driven by a motor, that puts an object in rotation around a fixed axis, applying a force that is perpendicular to the axis.
• The centrifuge works using the sedimentation principle, where the centripetal acceleration is used to separate substances of greater and lesser density.
• Svedberg unit – used to compare sizes of ribosomes – a measure of their density.
Process:
1. Centrifuge filtrate at low speed and remove pellet.
2. Repeat at increasingly higher speeds.
3. Each pellet removed contains structures of lower density.
Density gradient centrifugation.
• The cell-free extract is centrifuged in a dense solution
• Eg sucrose or caesium chloride
• The fractions separate out into layers with the densest fractions near the bottom of the tube.
Heaviest Nuclei
Mitochondria
Lysosomes
Lightest Ribosomes
[pic]
Cells
• Cell = the smallest unit of life.
• All living organisms are made of cells.
• There are unicellular organisms that consist of one cell:
o Bacteria
o Blue-green bacteria
o Protozoa
o Yeast
• These individual cells must carry out all of the essential life proceses
• Other organisms are made of many cells.
• These are multicellular organisms:
o Animals
o Plants
o Mushrooms
o Seaweed
• In these the life processes can be delegated to different organs and tissues.
Two main divisions of cells
• Prokaryotic cells:
o Bacteria
o Blue-green bacteria
• Eukaryotic cells
o Animals
o Plants
o Fungi
o Protoctista
• Pro = before
• Eu = true
• Karyo = nucleus
Prokaryotic Cells
• Example:
o Cholera – Vibrio cholerae
• Prokaryote = ‘before the nucleus’
• Simple cells containing no membrane bound organelles
• Considered to be the earliest form of life on Earth.
[pic]
|Structure |Function |
|Cell wall |Provide shape |
| |Protect against rupture by osmosis |
| |Some protection against other organisms |
| |Rigid |
| |Made of peptidoglycans – polymers of sugars and amino acids |
|Plasma membrane |Phospholipids and proteins |
| |Proteins include enzymes for metabolic processes |
| |Eg respiration, nucleic acid synthesis (in all) and photosynthesis (in some) |
| |Fluid mosaic |
| |Barrier for selective exchange of nutrients and waste products |
| |Movement by diffusion (including osmosis) and active transport |
|DNA |Singular, circular chromosome |
| |DNA helix |
| |In cytoplasm, not nucleus |
| |Attached to plasma membrane |
| |Eg E.coli 4 x 106 base pairs (A, C, T and G), about 4000 genes |
|Ribosomes |Smaller than in eukaryotic cells |
| |Site of protein synthesis |
|Flagella |Hollow cylinder |
| |Made of rigid protein strands (flagellin) |
| |Arise from basal bodies in plasma membrane in some bacteria |
| |Rotate from base like a rotor blade |
| |Bring about movement |
|Plasmids |Additional hereditary material |
| |Small rings of DNA, 10 – 30 genes |
| |In cytoplasm of some, not all, bacteria |
| |Eg antibiotic resistance |
| |Can be transferred through conjugation tubes |
| |Exploited as vectors in genetic engineering |
|Capsule |Tangled mat of polysaccharide fibres |
| |Slimy physical barrier |
| |Outer protective layer in some bacteria |
| |Protects against chemicals and dessication |
| |Protects against attack by phagocytic cells |
| |Helps bacteria to form colonies |
Eukaryotic Cells
[pic]
• Eukaryote = ‘true nucleus’
• These cells contain organelles
Cell membrane
• Thin layer found round the outside of all cells.
• Made of phospholipids and proteins.
• Controls the movement of materials in and out of cell.
Microvilli
• Small finger-like extensions of the cell membrane found in certain cells
• eg, epithelial cells of the intestine and kidney.
• Increase surface area.
Cytoplasm
• Watery solution within cell membrane.
• Contains:
o Enzymes for metabolic reactions
o Sugars, salts, amino acids in solution.
Organelles
• Membranous sacs.
• Compartmentalise portions of the cytoplasm.
• Increase the surface area for reactions.
• Allow metabolic reactions to be sequenced.
• Isolate potentially harmful chemicals.
Nucleus
• The largest organelle (10μm diameter).
• Controls cell’s activities.
• Store genetic material – chromosomes which are made of DNA.
• Spherical
• Surrounded by nuclear envelope:
o 2 membranes filled with fluid
• Nuclear pores enable mRNA to enter the cytoplasm.
• Interior is nucleoplasm which is full of chromatin (DNA/protein).
• Nucleolus is a dark region of chromatin, site of RNA transcription.
Mitochondrion
o Site of aerobic respiration in all eukaryotic cells.
o 2.5 to 5 micrometers long.
o Spherical or rod shaped
o Double membrane
o Inner membrane folded into cristae - large surface area.
o Internal space is the matrix, a solution of metabolites and enzymes.
o Also contain loops of DNA.
o ATP synthase (stalked particles) are on the inner membrane.
o Site of latter stages of respiration.
o Metabolically active cells contain numerous mitochondria.
o Number of cristae also increases with increased activity.
Ribosomes
o Smallest and most abundant ‘organelles’
o Not membranous
o Site of protein synthesis
o Made in nucleolus
o Made of protein and RNA
o Found either in cytoplasm or attached to the rough endoplasmic reticulum (RER)
o Larger type (80S)
o Often found in groups called polysomes
Endoplasmic reticulum (ER)
o An elaborate system of membranes.
o Forms part of the cytoplasmic skeleton.
o Extends from the nuclear membrane.
o Series of flattened stacks called cisternae.
o Enables substances to be synthesised and transported.
o Rough ER (RER)
o Studded with ribosomes, gives it rough appearance
o Polypeptides synthesised by ribosomes are passed into it.
o Pass proteins to Golgi body for further processing.
o Smooth ER (SER)
o No ribosomes.
o Involved in synthesising and transporting steroids.
Vesicles
o Small membrane bound organelles.
o Deliver substance around cell.
o Take substances:
o From ER to Golgi
o From Golgi to cytoplasm - lysosomes
o From Golgi to cell membrane for exocytosis – secretory vesicles
o Eg release of digestive enzymes.
Golgi body (Golgi apparatus)
o Series of flattened membrane sacs.
o Similar structure to ER.
o More compact and curved.
o Transports proteins from the RER to the cell membrane
o Vesicles of RER fuse with the Golgi on one side
o Contents of the vesicles enter the Golgi
o Steroids may be modified.
o Proteins may acquire tertiary/quaternary structure.
o Other groups may be added.
o Vesicles bud off the other side and move into the cytoplasm.
Lysosomes
o A type of vesicle.
o Contain enzymes.
o Used to breakdown unwanted toxins or organelles to recycle materials.
o Eg used in phagocytosis.
Summary of differences between prokaryotic and eukaryotic cells
|Prokaryotic cells |Eukaryotic cells |
|Extremely small ( ................
................
In order to avoid copyright disputes, this page is only a partial summary.
To fulfill the demand for quickly locating and searching documents.
It is intelligent file search solution for home and business.
Related download
- new bse letterhead
- guidelines on the prevention diagnosis
- transoesophageal echocardiography accreditation
- american society of echocardiography
- dr jake powrie s publications guy s and st thomas
- revised ordinance governing
- transoesophageal echocardiogram nursing management
- 3 biologypost
- consultation draft clinical evidence guidelines medical
Related searches
- activity 1 3 3 thermodynamics answer key
- activity 1.3.3 thermodynamics answer key
- act 1 3 3 thermodynamics answer key
- 3 3 t score bone density
- 3 by 3 linear system calculator
- 3 by 3 matrix solver
- 3 by 3 system solver
- 3 by 3 system calculator
- 3 equation 3 unknown solver
- 3 x 3 equation solver
- solving 3 x 3 linear systems calculator
- 3 3 repeating as a fraction