EMBED PBrush

EMBED PBrush

EMBED PBrush

Carbohydrates:

Monosaccharides: sweet, water soluble, reducing sugars

Disaccharides: sweet, water soluble, most are reducing (not sucrose)

Sucrose: Glucose + Fructose

Lactose: Glucose + Galactose

Maltose: Glucose + Glucose

Polysaccharides: long chains of repeating subunits (monosaccharides) joined by condensation reactions

Isomers: same molecular formula but a different structural formula

EMBED PBrush

EMBED PBrush

EMBED PBrush

Triglycerides

Fatty acid chains can be saturated (no C=C) or unsaturated (have C=C bonds). The more unsaturated the fatty acid the lower the melting point. Fats are insoluble ion water. A phospholipid has a fatty acid replace with a phosphate group. This means it has a hydrophilic region (phosphate head) and hydrophobic regions fatty acid tail. It is integral in the cell membrane.

EMBED PBrush

General fatty acid

Glycerol

Formation of a triglyceride

EMBED PBrush

Proteins

Polymers made up of amino acids.

EMBED PBrush

EMBED PBrush

Globular Proteins

The vast majority of proteins are globular, i.e. they have a compact, ball-shaped structure. This group includes enzymes, membrane proteins, receptors and storage proteins. The diagram below shows a typical globular enzyme molecule. It has been drawn to highlight the different secondary structures.

Globular Proteins

Have complex tertiary and sometimes quaternary structures.

Folded into spherical (globular) shapes.

Usually soluble as hydrophobic side chains in centre of structure.

Roles in metabolic reactions.

E.g. enzymes, haemoglobin in blood.

Fibrous (or Filamentous) Proteins Fibrous proteins are long and thin, like ropes. They tend to have structural roles, such as collagen (bone), keratin (hair), tubulin (cytoskeleton) and actin (muscle). They are always composed of many polypeptide chains. This diagram shows part of a molecule of collagen, which is found in bone and cartilage.

Fibrous Proteins

Little or no tertiary structure.

Long parallel polypeptide chains.

Cross linkages at intervals forming long fibres or sheets.

Usually insoluble.

Many have structural roles.

E.g. keratin in hair and the outer layer of skin, collagen (a connective tissue).

How the shape of the enzyme/protein molecules is suited to its function

Each enzyme/protein has specific primary structure (amino acid sequence)this sequence determines where the H-bonds will form during development of the secondary structure Proteins have a unique tertiary structure (further folding of the secondary structure) held by ionic and hydrogen bonds and if amino acids containing cysteine are present, disulphide bridgesGlobular proteins have an active site with unique structure;shape of active site complementary to/ will only fit that of substrate

Enzyme substrate complexes can form

Describe how enzymes break down substances

Lowering the activation energy

Substrate with a complementary shape to the active enters the active site

An enzyme substrate complex is formed

Active site changes shape to mould around the substrate (induced fit)

This weakens the bonds in the substrate (lowering activation energy) by stretching and distorting them

The bonds are broken

Products leave the active site

Enzyme remains unchanged

Describe how an enzyme catalyses a condensation reaction

Enzyme active site has a complementary shape to the substrate

An enzyme substrate complex is formed

The reactive groupshydroxyl, hydroxyl/ amino, and carboxylic / hydroxyl and carboxylic are brought close together

Change in the shape of the active site (induced fit) lowers the activation energy

Water is removed and a glycosidic, peptide or ester bond forms

Products leave the active site

The enzyme remains unchanged

The effect of temperature on the rate of an enzyme reaction

As temperature increases so does the rate of the reaction as

Substrate and enzyme gain K.E and collide more frequently

More enzyme substrate complexes form

Further increases in the temperature cause bonds (ionic, disulphide, hydrogen) holding the tertiary structure of the enzyme in place begin to break

The enzyme denatures,

The active site no longer complements the substrate

No enzyme substrate complexes can form

The effect of pH on the rate of enzyme activity

Changes in the pH affect the charges on the R groups of the amino acids at the active site

Interactions between the substrate and enzyme are disrupted

Enzyme substrate complexes are less likely to form

More extreme pH conditions can cause the bonds (ionic, Hydrogen) holding the tertiary structure to break

The enzyme denatures (active site is no longer complementary to the substrate)

No enzyme substrate complexes can form

Explain how inhibitors affect enzyme activity

There are two types of inhibitor, competitive and non-competitive

Competitive inhibitors have a similar shape to the substrate

They can enter and bind with the active site

Prevents enzyme substrate complexes forming

The problem can be overcome by increasing the substrate concentration

Non-competitive inhibitors

Have a different shape to the substrate

Bind at a point other than the active site

They cause a change in the shape of the active site

Prevent formation of enzyme substrate complexes

Explain how the small intestine is adapted to its function in the digestion and absorption of the products of digestion.

Large surface area provided by villi and microvilli

Thin epithelium gives a short diffusion pathway

The dense capillary network for absorbing amino acids and sugars and the lacteal for the absorption of digested fats; ensures a steep concentration gradient is maintained

The many mitochondria in the epithelial cells supply ATP/ energy for active transportCarrier proteins (in membranes) provide a path for polar molecules to pass through the membrane.

Enzymes built into the epithelial membrane make it more likely for enzyme substrate complexes to form and ensure products for absorption are released close to the carrier and channel proteins

Absorption of glucose in intestines

Glucose moves into the epithelial cell with sodium Via a symport carrier protein;

Sodium is removed from the epithelial cell by active transport at the sodium-potassium pump;

Maintaining a sodium concentration gradient between the lumen and epithelial cell

Glucose moves into blood by facilitated diffusion

And is carried away in the Heaptic portal vein

Digestion of Carbohydrates and Disaccharides

Starch Digestion:

Amylase

Hydrolyses

Glycosidic bonds

Producing maltose

Maltase hydrolyses maltose to glucose

Lactose intolerance

Cause: reduced lactase levels as we age

Symptoms: diarrhoea and gas and cramps

Explanation

Gas comes from bacteria breaking down the sugar

Diarrhoea: sugar lowers the water potential of the lumen compared to epithelial cells, water moves into the lumen by osmosis

Food moves through the digestive system by peristalsis.

Mouth = digestion of carbs

Stomach = digestion of protein

Duodenum = most digestion, receives pancreatic juice from pancreatic duct and bile form gall bladder (produced in liver)

Ileum = most absorption

Colon = absorption of water and minerals

Describe the structure of a cell membrane and phospholipids.

Described as fluid mosaic.

Fluid: molecules within the membrane able to move;Mosaic: mixture of phospholipid and protein

Double layer of phospholipid molecules;Phospholipid consists of glycerol;To which are joined two fatty acids;And a phosphate;formed by condensation reactionPhosphate head is hydrophilic/polar

Fatty acid tail is hydrophobicthe phospholipids are arranged as bilayer in membrane;

Heads on the outside and tails on the inside;

Intrinsic proteins molecules pass through entire bilayer

Some of the proteins have channels/pores;

Some have specific binding sites and are carrier proteins

Extrinsic proteins only in one layer

Those on the outer side often act as receptors for hormonesMolecules can move in membrane/dynamic/membrane containscholesterol;Many of the proteins and phospholipids have carbohydrates attached forming glycolipids and glycoproteins that make up the Glycocalyx

How the membrane regulates the movement of substances into and out of cells.

Non-polar/lipid soluble molecules move through phospholipid bilayer;Small molecules/water/gases move through phospholipid layer/bilayer;Ions/water soluble substances move through channels in proteins;Some proteins are gated;Reference to diffusion;Carriers identified as proteins;Carriers associated with facilitated diffusion;Carriers associated with active transport/transport with ATP/pumps;Different cells have different proteins;Correct reference to cytosis;

How plasma membrane is adapted for its functions.

Phospholipid bilayer (as a barrier);

Forms a barrier to water soluble but allows non-polar substances to pass so maintains a different environment on each side (compartmentalisation)

Bilayer is fluid: can bend to take up different shapes for phagocytosis and form vesicles

Channel proteins (intrinsic): let water soluble/substances through (facilitated diffusion)

Carrier proteins (intrinsic): allow facilitated diffusion and active transport

Extrinsic proteins: act in cell recognition, act as antigens or receptors;

Cholesterol: regulates fluidity / increases stability;

Membrane and Movement

The membrane is a phospholipid bilayer

Where the hydrophobic tails point inwards and the hydrophilic heads face outwards

The membrane contains two types of proteins

Intrinsic proteins (allow transport of water soluble molecules): spanning the entire bilayer

Extrinsic proteins: found on one side of the membrane

Most molecules move across the membrane by diffusion down a concentration gradient

Small molecules (water/gases) and lipid soluble molecules diffuse between the phospholipids

Polar molecules require channel or carrier proteins to move them

Channels are water filled pores that can be open at all times or they can be gated (voltage/ligand gated)

Carrier proteins have a specific binding site for the molecules/ions

This can be facilitated diffusion, a passive (no ATP required) process

Some molecules are actively transported across the membrane (against the concentration gradient)

This requires ATP (released in respiration)

The ATP changes the shape of the protein to move the molecule across the membrane

How proteins are arranged in a plasma membrane and role in transport

1 Some proteins pass right through membrane;

2 Some proteins associated with one layer;

3 Involved in facilitated diffusion;

4 Involved in active transport;

5 Proteins act as carriers;

6 Carrier changes shape / position;

7 Proteins form channels / pores;

8 Protein allows passage of water soluble molecules /charged particles / correct named example;

Describing the fluid-mosaic structure of a membrane

Phospholipids and proteins;Phospholipid bilayer: Arrangement of phospholipid molecules Tails to tails;Molecules can move in membrane;Intrinsic proteins extend through bilayer: Channel and carrier proteins

Extrinsic proteins in outer layer only: Act as antigens, receptors

Glycoproteins and glycolipids form glycocalyx Presence of cholesterol to help regulate fluidity

The phospholipids are arranged in a bilayer (i.e. a double layer), with their polar, hydrophilic phosphate heads facing out towards water, and their non-polar, hydrophobic fatty acid tails facing each other in the middle of the bilayer. This hydrophobic layer acts as a barrier to most molecules, effectively isolating the two sides of the membrane. Different kinds of membranes can contain phospholipids with different fatty acids, affecting the strength and flexibility of the membrane, and animal cell membranes also contain cholesterol linking the fatty acids together and so stabilising and strengthening the membrane.

The proteins usually span from one side of the phospholipid bilayer to the other (integral proteins), but can also sit on one of the surfaces (peripheral proteins). They can slide around the membrane very quickly and collide with each other, but can never flip from one side to the other. The proteins have hydrophilic amino acids in contact with the water on the outside of membranes, and hydrophobic amino acids in contact with the fatty chains inside the membrane.

EMBED PBrush

EMBED PBrush

EMBED PBrush

EMBED PBrush

EMBED PBrush

EMBED PBrush

Diffusion: net movement of molecules form a high concentration to a low concentration

Lipid soluble molecules can diffuse easily though the phospholipid bilayer along with small hydrophilic molecules like water, carbon dioxide and oxygen

Facilitated diffusion: a passive process, moving large, hydrophilic molecules down the concentration gradient. The molecules cannot pass though the hydrophobic bilayer and must enter/exit the cell through channel proteins or carrier proteins that are specific to the molecules.

Active transport

Moves a molecule against the concentration gradient (low to high)

Requires a specific protein carrier

Energy/ATP is used to change the shape of the protein

Energy is released in respiration

EMBED PBrush

Rate of movement of molecules in facilitated diffusion is limited by the availability of carrier/channel proteins in the membrane. As concentration increase rate will eventually level out as the channels or carriers are working at their maximum rate/ fully occupied.

EMBED PBrush

Mechanism of the heart beat

Cardiac muscle is myogenic

The SAN

Sends a wave of electrical activity (depolarisation) across the atria

This triggers atrial systole

The impulse is relayed to the ventricles through the AVN

Passing down to the apex of the heart along the bundle of His

The impulse spreads along the ventricle walls via the purkyne fibres

The ventricles contract from the bottom

The AVN delays ventricular systole to allow them to fill up with blood

Some key facts to learn

Valves in the heart and blood vessels prevent back flow

Tricuspid valve is on the right side of the heart

Bicuspid valve is on the left side of the heart

These two valves are called the atrioventricular valves

These valves are prevented from inverting as they are attached to the papillary muscle in the ventricle walls, by tendinous cords

Semilunar valves are located between the ventricles and the aorta and pulmonary artery. Rare for arteries to have valves

Pulmonary artery carries deoxygenated blood to the lungs. Rare for arteries to carry deoxygenated blood

Pulmonary vein carries oxygenated blood to the heart from the lung, rare for vein to have oxygenated blood.

Double circulation: blood flows through the heart twice for one circuit of the body, needs re-pumped after losing pressure in the lungs

Deoxygenated blood returns via the vena cava to the RA (1).

Atrium contracts blood through tricuspid into RV (2).

Ventricle contracts and tricuspid shuts so blood enters the pulmonary artery (3)

Blood returns to the LA (4) via the pulmonary vein.

The LA contracts and blood forced through the bicuspid valve into the LV (5).

The LV contracts and the bicuspid shuts and oxygenated blood flows into the aorta (6)

The left ventricle has a thicker, more muscular wall than the right ventricle as it has to pump blood around the whole body, so must generate a higher pressure.

When ventricular pressure > atrial pressure (1) the atrioventricular valves shut to prevent backflow, this is the first sound in the heart beat (lub)

When the ventricular pressure < arterial pressure (3) the semilunar valves shut, this is the second sound of the heart beat (dup)

QRS = electrical activity in the ventricles, occurs just before ventricle pressure increases

P = electrical activity in atria and P(Q = time delay due to AVN

Cardiac Output: is the amount of blood flowing through the heart each minute. It is calculated as the product of the heart rate and the stroke volume:

Cardiac output = heart rate x stroke volume

The heart rate can be calculated from the pressure graph by measuring the time taken for one cardiac cycle and using the formula:

Heart rate (beats/minute) = 60 time for 1 cycle

The stroke volume is the volume of blood pumped in each beat. Both the heart rate and the stroke volume can be varied by the body. When the body exercises the cardiac output can increase dramatically so that

Oxygen and glucose can get to the muscles faster

Carbon dioxide and lactate can be carried away from the muscles faster

Heat can be carried away from the muscles faster

Smokingdecreases conc. of antioxidants in blood: this increases the damage done to artery walls;raises the number of platelets in the blood and makes them more sticky :more blood clots are likely to form;causes constriction of coronary arteries: raises blood pressure and damage to the artery liningcarbon monoxide combines with haemoglobin so less available to transport oxygenblood pressure increased: due to increased heart rate

Fatblood cholesterol level increases;LDLs transport cholesterol in the blood;LDLs deposit cholesterol in arteries

atheroma formedblood pressure increased, turbulence makes clotting more likely

SaltIncreased salt concentration in blooddecreases water potential of the bloodwater moves into the bloodblood pressure increased

How atheroma causes an aneurysm

Fatty material within walls of arteries;Vessels narrow;Blood pressure rises;Weakened blood vessels may burst;

Describe how atheroma may form and lead to a myocardial infarction

Cholesterol deposited in the artery wall

This atheroma narrows lumen of the artery

This creates turbulence and can damage to lining of arteryTurbulence increases risk the of blood clot (thrombus)The blood clot may break off (embolus)And lodge in coronary artery;Reduced blood supply to heart muscle;Reduced oxygen supply;

Reduced respirationLeads to death of heart muscle

Atheroma:

A build-up of cholesterol

in the artery wall

There are thousands of different kinds of cell, but the biggest division is between the cells of the prokaryote kingdom (the bacteria) and those of the other four kingdoms (animals, plants, fungi and protoctista), which are all eukaryotic cells.

Prokaryotic cells are smaller and simpler than eukaryotic cells, and do not have a nucleus.

Prokaryote = without a nucleus

Eukaryote = with a nucleus

To see cells we need microscopes, like a light microscope. To see the ultrastructure of a cell (the organelles inside) we need electron microscopes.

20m

If given a scale bar as below then the formula to use is

Actual length of scale bar

Magnification =

Representative length of the scale bar

Ensure you work in the same units

Cm ( mm ( m ( nm

10

1000

1000

If no scale bar is given then the formula to use is

Image Size

Magnification =

Actual Size of image

Ensure you work in the same units and then convert to the units they want at the end

Resolution: how close 2 points can be to each other and still be distinguished as 2 separate points.

Electron microscopes have a higher resolution than (light microscopes, as they use electrons that have a shorter wavelength than light

Shorter wavelengths (like electrons) allow better resolution than longer wavelengths (like light).

Explain the advantages and limitations of using a transmission electron microscope

Advantages

1 TEM uses (beam of) electrons;

2 These have short wavelength;

3 Allow high resolution/greater resolution/Allow more detail tobe seen/greater useful magnification;

Disadvantages

4 Electrons scattered (by molecules in air);

5 Vacuum established;

6 Cannot examine living cells;

7 Lots of preparation/procedures used in preparing specimens/ fixing/staining/sectioning;

8 May alter appearance/result in artefacts;

9 very thin specimens

10 black and white, images

How to use a microscope to measure the size of an object.

Measure with an eyepiece graticule

Calibrate with the stage mcirometer (an object of a known size)

Repeat and calculate an average

Magnification and Resolution

Magnification simply indicates how much bigger the image is that the original object. It is usually given as a magnification factor, e.g. x100. By using more lenses microscopes can magnify by a larger amount, but the image may get more blurred, so this doesn't always mean that more detail can be seen.

Resolution is the smallest separation at which two separate objects can be distinguished (or resolved), and is therefore a distance (usually in nm). The resolution of a microscope is ultimately limited by the wavelength of light used (400-600nm for visible light). To improve the resolution a shorter wavelength

of light is needed, and sometimes microscopes have blue filters for this purpose (because blue has the shortest wavelength of visible light).

Electron Microscopes

This uses a beam of electrons, rather than electromagnetic radiation, to "illuminate" the specimen. This may seem strange, but electrons behave like waves and can easily be produced (using a hot wire), focused (using electromagnets) and detected (using a phosphor screen or photographic film). A beam of electrons has an effective wavelength of less than 1nm, so can be used to resolve small sub-cellular ultrastructure. The development of the electron microscope in the 1930s revolutionised biology, allowing organelles such as mitochondria, ER and membranes to be seen in detail for the first time.

There are two kinds of electron microscope.

Transmission electron microscopes (TEM) work much like a light microscope, transmitting a beam of electrons through a thin specimen and then focusing the electrons to form an image on a screen or on film. This is the most common form of electron microscope and has the best resolution (