1 Causes Of Disease
- Microorganisms include bacteria, fungi and virus.
- Some microorganisms can be beneficial to our health.
- Certain microorganisms cause disease, these are known as pathogens.
- Disease is a description of certain symptoms which can be physical or mental.
Microorganisms as Pathogens
- To be a pathogen a microorganism must:
- Gain entry to the host.
- Colonise the tissues of the host.
- Resist defences of the host.
- Cause damage to the host tissues.
- When a pathogen gets into a host and colonises this is an infection.
- Disease occurs when infection leads to symptoms.
- Transmission is when a pathogen is transferred to someone.
How do microorganisms get into the body?
- Pathogens enter by penetration an organism's interfaces
- The skin acts as a barrier to infection since it is thick and continuous
- If the skin is broken e.g. cut, pathogens can get in
- The body linings are thin, moist, have large surface area and have good blood supply, this allows entry for pathogenic microorganisms.
- Entry points include:
- Gas Exchange System e.g. pathogens like influenza and tuberculosis
- Digestive System e.g. food and water carries pathogens into stomach like cholera and typhoid.
- The body has natural defences:
- Mucous layer covers exchange surfaces to form barrier
- Enzymes break down pathogens
- Stomach acid kills microorganisms
How Pathogens cause disease
- Pathogens affect the body in two main ways:
- Damaging host tissues
- Producing toxins
- Diseases can have many causes such as pathogens, lifestyle and genetics
- The Faster a pathogen divides the quicker symptoms appear
1.2 Data and Disease
Correlations and Causal Relationships
- Correlation occurs when a change in one of two variables is reflected by a change in the other
- When just one factor has caused a change in a variable it is said to be causal
- If there are other factors to consider then there is a correlation NOT causation
Is the Data reliable?
- Was the right factor measured which the right questions asked?
- How was data gathered?
- Who is collecting the data do they have a motive?
- Has the study been repeated with similar results?
- Still unanswered questions?
1.3 Lifestyle and Health
What is Risk?
- A measure of the probability that damage to health will occur as a result of a given hazard
- Risk has two elements: probability of a hazardous event and consequence of the event
Cancer Risk Factors
- Causal factors can be age and genetic
- Some factors like lifestyle can be changed
- Things that contribute to cancer:
- Little Physical activity
Lifestyle and Health Continued
Coronary Heart Disease (CHD)
- High Blood Pressure: due to prolonged stress, certain diets and lack of exercise
- Blood Cholesterol Levels: reduced by lowering saturated fatty acids
- Diet: high salt raises blood pressure, high saturated fatty acids increase blood cholesterol
- Physical Activity: Aerobic lowers blood pressure and cholesterol, reduces obesity
All these factors can be changed reducing the risk of CHD and Cancer
2 Enzymes and the Digestive System
Enzymes and Digestion
- Glands of the digestive system produce enzymes
- The enzymes break large molecules into smaller ones for absorption
- The digestive system provides an interface due to having food substances entering it
Major parts of the Digestive System
- Oesophagus: carries food from mouth to stomach, made up of thick muscular wall
- Stomach: muscular sac with inner layer that produces enzymes, stores and digests food, glands in the stomach produce mucus stops the stomach digesting its enzymes
- Small Intestine: Long muscular tube, food is further digested, inner walls folded into villi giving large surface area, villi have microvilli allowing for absorption of digestion products into blood
- Large Intestine: absorbs water forming the faeces
- Rectum: Faeces are stored before removed via egestion
- Salivary Glands: near mouth, contain amylase which breaks down starch
- Pancreas: large gland below stomach, produces secretion containing proteases, lipases and amylase
Enzymes and Digestion Continued
What is Digestion
- It takes place in two ways:
- Physical Breakdown: food broken down into smaller pieces e.g. by teeth, creates a large surface area, food is also churned by stomach muscles
- Chemical Digestion: Large insoluble molecules broken down using enzymes by hydrolysis
- Enzymes are specific so more than one is needed to break large molecules
- Carboydrases: break down carbohydrates to monosaccharides
- Lipases: Break down lipids to glycerol and fatty acids
- Proteases: Break down proteins to amino acids
- The products are absorbed into the bloodstream and then used to form large molecules again.
- The molecules are incorporated into body issues which is assimilation.
2.2 Carbohydrates- Monosaccharides
- Carbohydrates contain carbon, oxygen and hydrogen.
- Carbon readily bonds with other carbons allowing various sequences of carbon.
- Every living thing is based on carbon
Making Large Molecules
- Individual molecules that make up a chain is a monomer.
- The carbon atoms join to form longer chains known as polymers
- Polymers can be made up of carbon, hydrogen, oxygen and nitrogen
- In carbohydrates the basic monomer unit is sugar (saccharide)
- Single monomer is a monosaccharide, a pair is a disaccharide and larger are known as polysaccharides
Carbohydrates- Monosaccharides Continued
- Sweet tasting, soluble substances
- General formula (CH2O)n
- Glucose is a monosaccharide , it is a hexose sugar (C6H12O6)
Test for Reducing Sugars - Benedict's Test
- Monosaccharides and some disaccharides are reducing sugars
- Reduction involves the gain of electrons
- A reducing sugar is a sugar that can donate electrons, in this case Benedict's reagent
- Benedict's is an alkaline solution of Copper (II) Sulfate
- Add the food sample to a test tube making sure it is liquid
- Add equal Benedict's reagent
- Heat the mixture gently for 5 minutes it should turn orange/brown
2.3 Carbohydrates-- Disaccharides and Polysacchari
- Glucose-Glucose = Maltose
- Glucose-Fructose = Sucrose
- Glucose-Galactose = Lactose
- The reaction to form a disaccharide is called a condensation reaction since a molecule of water is removed, a glycosidic bond is formed
- When water is added to a disaccharide the glycosidic bonds are broken this is hydrolysis
Test for Non Reducing Sugars
- Disaccharides e.g. sucrose are non reducing sugars
- To detect them you must first break them down into the monosaccharides
- Add Benedict's solution to the liquid food sample and gently boil
- If it remains blue a non reducing sugar is present, add hydrochloric acid and boil
- The acid hydrolysis the disaccharide, add sodium hydrogencarbonate to neutralise it
- Retest by adding Benedict's reagent and boiling, it should bow turn orange/brown
Carbohydrates-- Disaccharides and Polysaccharides
- Monosaccharides are joined by glycosidic bonds to form polysaccharides
- The bonds are formed in a condensation reaction
- Polysaccharides are insoluble so are suitable for storage
- Cellulose is a polysaccharide used for structural support in plant cells
- Starch is found in many parts of plants as small granules of grains.
- Starch is formed by linking 200 - 100000 alpha glucose molecules by glycosidic bonds
Test for Starch
- Starch changes the colour of iodine in potassium iodide solution
- Add the sample to a test tube then add to drops of iodine solution and shake
- The solution should turn from yellow to blue/black at room temperature
2.4 Carbohydrate Digestion
- Food is chewed up by the teeth giving a larger surface area
- Salivary glands produce amylase which hydrolyses the starch into maltose by breaking alternate glycosidic bonds of the starch
- The food passes into the small intestine where more amylase hydrolyses the starch
- Epithelial lining of the small intestine produces maltase which hydrolyses the maltose into alpha glucose
- Sucrose is usually contained in cells so the teeth physically break them down
- Epithelial lining releases sucrase which hydrolyses the single glycosidic bond producing the monosaccharides glucose and fructose
- It is found in milk and is digested in the small intestine by lactase
- Lactase hydrolyses the glycosidic bond that links glucose and galactose
- Since milk forms a lower part of adult diets lactase production diminishes.
- This reduction can be so drastic that they produce little to no lactase
- If undigested lactase reaches the large intestine microorganisms break it down.
- The microorganisms produce gas which causes bloating, nausea and cramps
- Main difficulty is getting enough calcium and vitamin D in absence of milk
- Special none milk food is provided
- Proteins are very large molecules
- Enzymes are proteins which are involved in almost every living process
Structure of an Amino Acid
- Amino acids are basic monomer units that combine to form the polymer, polypeptide
- Polypeptides combine to form proteins
- Every amino acid has a central carbon atom that has; an amino group (NH2), carboxyl group (COOH), hydrogen atom and R group
The Formation of a peptide bond
- Amino acids combine to form dipeptides due to condensation reactions
- The OH from the carboxyl group and the H from the other amino acid join.
- A peptide bond between the carbon and nitrogen forms
The Primary Structure - Polypeptides
- Many amino acids can join in condensation in a process called polymerisation
- Hundreds of amino acids joined form a polypeptide
- The sequence of amino acids in a polypeptide chain forms the primary structure
- There are almost limitless combinations and primary protein structures
- Primary Structure determines ultimate shape and function
- Changing a single amino acid in the sequence leads to a shape change thus a stop in function
The Secondary Structure
- The linked amino acids posses both NH and C=O groups on either side of every peptide bond
- The Hydrogen of the NH has an overall positive charge and the O of the C=O has a negative charge, these groups form hydrogen bonds
- This causes the polypeptide chain to twist into a 3D shape known as an alpha helix
- The Alpha helix can be twisted even more this is the tertiary structure
- Bonds that are included:
- Disulfide bonds: fairly strong
- Ionic bonds: formed between carboxyl and amino groups (not involved in peptide bonds)
- Hydrogen bonds: easily broken
- The 3D shape is important as it makes the protein distinctive and allows it to recognise, and be recognised by other molecules
- Large molecules often form complex molecules containing individual polypeptide chains
- Also non-protein (prosthetic) groups associated with the molecules
Test for Proteins
- Add sodium hydroxide solution to the sample add few drops of dilute copper (II) sulphate and mix, if a protein is present goes from blue to purple
2.6 Enzyme Action
- Enzymes are globular proteins that act of catalysts
- They speed up the reaction that occur
Enzymes as Catalysts lowering activation energy
- For reactions to take place:
- The substrates must collide with sufficient energy to change arrangement of their atoms
- Energy of products must be less than substrates
- Activation Energy: minimum energy required to activate the reaction
- Enzymes specific shape is due to sequence of amino acids
- The active site of the enzyme is a small region, it forms a small hollow depression within the larger enzyme molecule
- When the substrate and enzyme bind it is called the enzyme-substrate complex
Enzyme Action Continued
Lock and Key model of enzyme action
- Enzymes work like a lock and key
- The enzyme has a fixed shape that the substrate fits into
- This idea is limited as it suggests that enzymes are rigid however it is actually flexible
Induced fit model of enzyme action
- Enzymes change shape to fit the substrate, it moulds itself around it
- As it changes shape it puts pressure on the substrate which distorts a particular bond lowering the activation energy
- This model is better than the lock and key since it explains better how other molecules affect enzyme activity and how activation energy is lowered
2.7 Factors affecting enzyme action
- Temperature rise increases the kinetic energy of molecules
- Molecules move more rapidly and collide more often
- After a certain temperature the enzymes become denatured
- Denaturation is a permanent change that stops the enzyme functioning
- pH measures the hydrogen ion concentration
- Each enzyme has an optimum pH
- pH change alters charges on the amino acids that make up the active site stopping it from allowing the substrate to bind
- Cause bonds to break that maintain tertiary structure causing it to change shape
- Arrangement of the active site depends partly on the hydrogen and ionic bonds between NH and COOH groups of the polypeptides that form the enzymes
- Change in H+ ions affects the bonding changing the active site
Factors affecting enzyme action continued
Effects of Substrate Concentration on the Rate of Enzyme Action
- If enzyme amount is fixed at a constant level and substrate slowly increases the rate of reaction increases.
- Since with low substrate concentration enzymes have limited substrate to collide with so active sites won't work to full capacity
- More substrate added the active sites become filled until they work as fast as they can
- Rate of reaction reaches its maximum
- When there is excess substrate the rate of reaction levels off.
2.8 Enzyme Inhibition
- Enzyme Inhibitors directly/indirectly interfere with the active site functioning
- There are two reversible inhibitors:
- Competitive: bind to active site
- Non-Competitive: bind to other position
- Molecular shape similar to substrate so can occupy the enzyme
- They compete with the substrate for the active site
- If substrate concentration is increased the effect of the inhibitor is reduced
- The inhibitor isn't permanently bound so other molecules can replace it
- Example: The respiratory enzyme that acts on succinic acid can be bound to malonic acid instead blocking the succinic from combining with the active site
- This inhibitor alters the shape of the enzyme active site so substrate cannot attach
- An increase is substrate doesnt decrease the inhibitor's effect