Food Science - Metabolic Pathways- a level biology revision

Detection of light in flowering plants

2007-12-19T10:24:00.000-08:00

photoreception if the detection of light. this usually involves the absorption of light by a pigment known as a photoreceptor.
Light is important to plants because of the formation of chlorophyll, photosynthesis, initiates flowers, germniation and direction of growth.
Plants grown in dark condititons are said to be etiolated having yellow leaves, taller and thinner.
in the early stages of life this is an advantage as it can push through the soil more easily, faster growth to reach light wicker.

phytochrome is the photoreceptor, its a blue-green pigment present in small amounts in the leaves. it exists in two interconvertible forms Pfr and Pr.
Pr absorbs red light and is converted into Pfr, This is fast and is done in the light
Pfr absorbs far red light is converted into Pr, this is slow and is done in the dark
Pfr acts as a daylight length detector system.
Pfr promotes the flowering of long day plants
Pfr inhibits the flowering of short day plants

Germination:
seeds must take in water( IMBIBITION)
This causes the embryo to release gibberellic acid and this induces the synthesis of hydrolyic enzymes , including amylase.
Hydrolysis of starch takes place and it is broken down to maltose, this fuels respiration in the embryo so it an grow.

The Central Nervous System

2007-12-18T11:39:00.000-08:00

this consists of the brain and spinal cord. it creates appropriate responses to sensory info.
the nervous system is first divided into the cns and the peripheral nervous system.
this consists of the crainial nerves.
brain parts:

cerebral hemisphere- 2 which make up the cerebrum, the largest part. connected by nerve fibres called the corpus callosum.
receives impulses from sensory receptors e.g. heat, cold, touch , sight, taste, smell
controls skeletal movements for voluntary movement
consciousness, memory, language, speech, emotions.

Hypothalamus-synthesis of hormone, osmoregulation and maintains body temperature.

Midbrain- conducts impulses between the hindbrain and forebrain, linked with visual and auditory reflexes.

cerebellum- acts with the cerebrum to produce skilled co ordinated movements, co ordinates balance and posture.

Pons-mainly nerve fibers joining the parts of the cerebrum, control of breathing.

Medulla Oblongata-controls rate and force of heartbeat, coughing, sneezing vomiting etc

The brain develops in the embryo from a neural plate.
fold arise and form a neural tube

3 main sections: forebrain contains: cerebrum and hypothalamus
midbrain contains: midbrain
Hindbrain contains: pons, cerebellum and medulla oblongata.

Spinal Cord- continuous with the medulla oblongata, there are 31 pairs of spinal nerves arise from the cord. It consists of a central area of Grey matter and an external layer of white matter. int he center is a central canal of fluid.
they grey is unmyelinated these neurone go to the skeletal muscles
the white matter are neurones going to the brain.

spinal reflexes: the effector neurone is stimulated by a neurone orginiating from the spinal cord.
a relay neruone links sensory and effector.

A reflex action is an immediate response to a sensory stimulus.
reflex arc:

withdrawal reflexes are for example moving rapidly away from a harmful simulus.
muscle stretch reflexes include two neruones sensory and effector. e.g knee jerk.

Nervous co-ordination

2007-12-16T08:39:00.000-08:00

The nervous and endocrine systems work together to co ordinate the actions withing the body.

Nervous system:
info is passed as electrical impulses along nerve fibres and chemically over synapses.
Transmission is relatively rapid with a short response time. however it is short lived.
the response is very local as 1 nerve fibre supplies a group of effector cells.

endocrine systems:
info is passed as chemical substances in the bloodstream/plasma.
transmission is relatively slow and the response time is long, the response may carry on for a long time.
the response can be widespread and cells in different parts of the body can respond to the chemical.
cell body: contains the nucleus and mitochondria. providing atp for sodium/ potassium pump.
dendrites: increase the surface areas many synapses can be made with other neighboring neurones.
axon: transmit electrical impulses away from the cell body, they are long so there are fewer synapses to slow it down.
myelin: enclcoses the axon, fatty sheath. insulates, speeds up conduction and prevents action potentials being formed.
Nodes of ranvier: gap in the myelin sheath where action potentials can form.
synaptic bulbs: end of the branch the axon contains vesicles of neurotransmitters.

3 types of neurones:
1) sensory neurones- conduct nerve impulses away from a receptor toward the central nervous system.
2) relay neurones- conduct impulses from the sensory neurones to a motor neurone.
3)motor(effector) neurones conduct nerve impulses from a relay neurone in the spinal cord to an effector e.g a muscle.

myelination and schwann cells
schwann cells produce the fatty myelin surrounding the axon. the schwann cell wraps around the axon, covering it.
The action potentials move from each node of ranvier to the next.(saltatory conduction)
as the schwaan cell grows around the axon it twists many times and myelin is formed from the layers of schwaan cell membrane pressed together.

The Nerve Impulse:
potential differences are caused by uneven distribution of positively charged ions, on either side of the nerve cell membranes.
A resting potential exists when there is no nerve impulse.

outiside there is high Na+ and low k+
overall more positive outside = resting potential of -60mV
inside low Na= and high K
there is more k channel than na channels and 3na ions move out and 2 k move in .

Synapse:
in most synapses the gap is too large for electrical impulses to jump across and instead the impulse triggers the release of the chemical transmitter.

mechanisms for synaptic transmission
1) the action potential reaches the bulb of the presynaptic membrane, calcium channels open and calcium diffuses in.
2) calcium simulates the movement of vesicles to the membrane.
3) the vesicles fuse with the membrane and release their transmitter by exocytosis into the synaptic cleft.
4) the transmitter diffuses across and binds to receptors on the postsynaptic membrane, this causes ion channels to open.
5) the movement of ions results in the generation of a postsynaptic potential.
6) the transmitter substance is quickly broken down by enzymes.

Hormones in mammals

2007-12-16T03:57:00.000-08:00

secreted by endocrine glands (into the blood capillaries).
are transported in blood plasma.
regulate changes in the internal environment
help homeostasis
may promote actions or inhibit effects
cause slow effects which are longer lasting.
affect a specific target organs

3 main groups:
1) amines: e.g. adrenaline from the medulla of adrenal glands.
2)peptides and proteins e.g. insulin and glucagon
3) steroids e.g. testosterone and oestrogen

released due to 1 of 3 types of stimulus:
1)presence or change in concentration of a substance
2) presence of change in concentration of another hormone
3) nervous stimulation e.g. adrenaline secreted from the adrenal medulla

hormone-------------site produced------------when-----------effect
insulin---------------beta cells-----------high glucose conc'-----reduced blood sugar
glucagon------------alpha cells----------low glucose in plasma---increases blood sugar
adrenaline----------adrenal meulla------nervous stimulation----incrse bld glucse & mre blood 2
ADH----hypothalamus-strd in pit gland--low blood water---increase water absorption in kidney
FSH--------anterior pit gland---------------------stims osestrogn and follicles in ovar develope
LH---------------pituitary---------------------------------stimulates ovulation
oestrogen----------ovary----------------menstrual cycle-----------stims endometirum
progesterone-----ovary---------------menstrual cycle-----------maintains endometrium
oxytocin-----------------------------during child birth--------stimulates contractions
prolactin---------ant pituitary---------after birth--------stims mammaries to produce milk

Endocrine: ductless gland

Exocrine: has a duct

Human eye

2007-12-03T10:23:00.000-08:00

Light sensitive cells respond to the light resulting in action potentials being sent along the optic nerves to the visual cortex at the back of the cerebrum.

Key terms:

Conjuctiva- protective, thin layer of epithelial cells
Cornea- curved front of the eye, transparent and helps converge light rays
sclera: fibrous, outer protective structure.
choroid: supplies nutrients to all cells and removes waste, pigmented to prevent internal reflection. it has a network of blood cells.
Iris: muscular structure with an inner ring of circular muscle and an outer layer of radial muscle. it controls the amount of light entering the eye.
Pupil: hole in the middle of the iris where light continues into the eye
Vitreous humour: jelly like mass located behind the lens, it suspends the lensso it is not damaged.
Lens: transparent, flexible, curved structure. focus's incoming light onto the retina as it is refractive.
Retina: layer of sensory neurones, photoreceptors which respond to light. the rods and cones
Blind spot: this is where the bundle of sensory fibers form the optic nerve.
Uses of ATP: resynthesis of rhodopsin / sodium pump

A receptor is a cell or group of cells that detect a specific stimulus.

Rod cells:sensitive to light intensity. not sensitive to colour. they can respond to very dim light.
rhodopsin ---light---> opsin + retinal

Rhodopsin is stored in flattened membranous vesicles
low visual acuity in dim light.
opsin opens ions channels for the generation of action potentials.

Rod cells are absent in the fovea
The inner segments have lots of mitochondria which provide atop for the resynthesis of rhodopsin.
Rhodopsin is regenerated when there is no light. These are used at Night

a generator potential is produced which causes nerve impulses to be transmitted along a sensory neurone. Hyperpolarisation then depolarisation.
you have many 3/4 rods to one bipolar and ganglion cell.

around 120 million per retina

light hitting the pigment causes it to split.opsin iniates reaction ledin to the surafe becoming negative. Hyperpolarisation. When this reaches past a threshold, an action potential is stimulated in the sensory neruone. and this passes to the brain. this is to the visual cortex

Cone cells: require high light intensity to be stimulated. High visual acuity.
iodpsin----> photopsin + retinal
3 different types:
red-stimulated by red light
green- '' green light
blue- '' blue light
there are less cones than rods, and they are more focussed around and at the fovea.
Trichromatic theory states, colour vision is perceived according to the degree of stimulation of each type of cone.
1 cone cell is connected to 1 bipolar and ganglion cell.
6-7 million per retina.
Ganglion cell: transmitts action potential along neruones.
Bipolar cell:form an intermeidiate which connect photosensitive cells to ganglion cells.

Iris/pupil reflex:
the amount of light coming into the eye is detected by recpetors in the retina. reflex pathways lead to the circular and radial muscles of the iris contracting or relaxing.
High intensity light, leads to constricted pupils (small) circular muscle contract and radial relax.
low intensity light, leads to a dilated pupil (large) circular muscles relax and radial contract.

2007-11-20T11:52:00.000-08:00

The creation of new glucose is GLUCONEOGENESIS

A rise in blood glucose concentration:
1) receptors pick up that there is high glucose in the blood
2) the beta cells in the islets of Langerhans secrete insulin directly into the blood stream.
3) insulin increases the permeability of of cell membranes to glucose , so more glucose is absorbed.
4) Insulin also activates the condensation of glucose to glycogen in glycogenesis
5) insulin also increases the rate of respiration of glucose.
6) blood glucose decreases

A decrease in blood glucose concentration:
1) alpha cells of the islets of Langerhans secrete glucagon into the blood stream.
2) this activates the hydrolysis of stored glycogen to glucose . this is called glycogenolysis
3) blood glucose increases

Pancreas:
key organ in controlling blood glucse levels
cells are known as the islets of langerhaans, are endocrine function.
Alpha cells secrete: glucagon
beta cells secret: insulin

these hormones are secreted straight into the blood capillaries
they are antagonistic

Insulin is a hormone that decreases the level of glucose in the blood. Two effects of insulin are cells are more permeable to glucose, speeds up acquisition. it also activates enzymes stimulation the conversion of glucose to glycogen.
Its main target organs are the Pancreas, Liver, muscles.

Glucagon hormone that increase blood sugar, main effect is that it activates enzymes which are responsible for converting glycogen into glucose (glycogenolysis)

the brain only respires glucose

glycogenesis: the synthesis of glycogen from glucose under the influence of insulin

glycogenolysis: the breakdown of insoluble glycogen under the influence of glucagon to form glucose.
gluconeogenesis: the creation of glucose from non carb sources e.g. lipids/ fatty acids or protein.

test for glucose:
diabur strips, yellow= no glucose,
progressively darkgreen-blue= glucose present

Benedicts test:(less sophisticated)
not specific to glucose just for redcuing sugars
after heating for 3 mins a blue solution means no glucose.
a brick red means glucose

The kidney

2007-11-13T01:31:00.000-08:00

The kidney
The kidneys are organs that filter waste products out of the blood and excrete then e.g. urea along with water as urine.
Urea is made by the liver. Excess amino acids can’t be stored therefore the liver breaks them down to urea.(ornithine cycle)
OSMOREGULATION: The homeostatic mechanism of the active regulation of the osmotic pressure of bodily fluids to maintain the homeostasis of the body’s level of water, minerals and salts in the blood.
NITROGENOUS EXCRETION: excretion of nitrogen in urine.

The kidney is involved with the homeostatic functions of regulating the chemical properties of the blood. (Water, solvent concentration and pH)

When the blood passes through the kidney nephrons liquid is filtered out of the blood, carrying solutes with it, including urea. Useful nutrients are selectively reabsorbed and the wasted products are removed in urine.
There are two main stages of kidney function:

1) ULTRAFILTRATION
This occurs in the barrier between the blood and the filtrate in the Bowman’s capsule. In the Bowman’s capsule there is a dense network of capillaries called the glomerulus, blood flows into the capillaries.
A glomerulus is enclosed in the sac. Fluids from blood in the glomerulus are collected in the Bowman's capsule (i.e., glomerular filtrate) and further processed along the nephron to form urine. This process is known as ultrafiltration.
A high pressure caused by the blood moving into the capillaries via the afferent wide arteriole and moving out through the narrow efferent arteriole. The high pressure forces small molecules such as water, glucose, amino acids, sodium chloride and urea through the filter, from the blood in the glomerular capsule across the basement membrane of the Bowman's capsule and into the nephron. This type of high pressure filtration is ultrafiltration.
Blood is forced against the capillary endothelium which has pores in it which allow the blood plasma to reach the basement membrane and small molecules are squeezed about but large ones like protein and blood cells stay in.

2) Selective reabsorption (proximal tubule)
Selective reabsorption takes place in the proximal convoluted tubule (PCT) of the kidney. Blood leaving the Bowman’s capsule has a low hydrostatic pressure and so flows slowly. It has a high concentration as these could not pass out before. It therefore has a low water potential and this enables it to gain water from the proximal tubule. It is the process by which certain substances that are required by the body (such as glucose, amino acids, vitamins and water) but have been filtered out of the blood during ultrafiltration are reabsorbed. As only certain substances are reabsorbed, it is known as selective reabsorption.

substances secreted into the distal convoluted tubule are: h+ ions and potassium ions.
substances actively reabsorbed from the proximal convoluted tubule are sodium ions and glucose.
the kidney tubule has adaptation such as lots of mitochondria and a brush border for atp for the active reabsorption of molecules and a large surface area for absorption.
overview: sodium ions are actively pumped out, glucose reabsorbed, amino acids reabsorbed and chloride reabsorbed, 50 % urea reabsorbed

ADH makes the collecting duct more permeable to water. So more water is taken back into the body by osmosis. more water is taken back into the blood stream and less is lost in urine. It is secreted by the posterior pituitary gland. Osmoreceptors detect changes in the hypothalamus.

Urine: composition varies due to diet and climate.

Unbalanced diet and diseases

2007-11-08T09:33:00.000-08:00

Under nutrition

A lack of protein in the diet is called protein-calorie malnutrition. This is commonly found in the developing world in poorer countries.
Conditions caused by lack of protein:

Marasmus- malnutrition caused by a diet low in protein and energy/carbohydrates. Also caused by early weaning off breast milk. Suffers are grossly underweight, they have thin arms and legs, no body fat and muscle is wasting away.

Kwashiorkor- malnutrition caused by low protein only. usually occurs in slightly later age than marasmus. Suffers have oedema (swelling) in the feet and lower legs, pale thin hair, muscle wasting and a moon face.

Anorexia nervosa and bulimia nervosa are malnutrition due to psychological issues.

Two examples of Under-Nutrition are Anorexia nervosa and Bulimia nervosa.
These are examples of poor dieting, resulting in a lack of essential nutrients. They are eating disorders and the under-nutrition is self induced.
Anorexia nervosa usually starts in the teenage years, mainly affecting women and girls but boys can be affected.
The disease is characterised by a list of symptoms:
1. Body weight is maintained at 15% below that expected for a persons height.
2.Self induced weight loss, from forced vomiting, taking laxatives, avoiding fatty foods and excessive exercise.
3. Fear of putting on weight, obsessed with the size of their body.
4. Pursue a very low ideal weight.
5. Can cause hormonal differences and women can stop having periods.

Normally seen in the western world, from social and biological factors, peer pressure, media and stress can cause Anorexia nervosa.

6. Delayed development of puberty.
7. Feel bloated after a small meal.
8. loose interest of socializing with friends
9. They feel tired
10. Constipation
11. Feeling cold
12. Low blood pressure

Can lead to:
1.Chronic illness
2. Death
3. Osteoporosis
4. Damage to heart, kidneys, liver and brain.
5. Difficulties in concentration
6. Mental health problems

Bulimia nervosa

This is another eating disorder which involves an irresistible urge to 'binge' eat on food, followed immediately by self induced vomiting. laxatives etc are used as well to prevent weight gain.
Vomiting can lead to loss of potassium, chloride and hydrogen ions.

symptoms:
1. Dental erosion
2. Sore throat
3. Swollen salivary glands
4. Fatigue
5. Constipation
6. loss of voice
7. dry skin, brittle nails
8. Anemia
9. Infertility
10. Liver failure

people who suffer from Bulimia nervosa do not show the symptoms of extreme weight loss.
The person will be of normal or higher weight, the person is less likely to drop significant amounts of weight.
This is less to do with food but more with psychological issues.

Vitamin A
retinol is found in dairy products and fish liver oils. It is needed to keep lining tissues healthy.(epithelium). Deficiency leads to night blindness.

Vitamin C
Ascorbic acid is found in citrus fruits, green vegetables etc. it is needed for hydroxylase to work. It maintains collagen fibres in connective tissue. Deficiency is scurvy as the connective tissue weakens.

Calcium
Found in dairy products, bread and flour. calcium is absorbed through the small intestines by carrier proteins. The carrier can only be made with vitamin D. lack of vitamin D can lead to calcium deficiency. This leads to rickets, muscle spasms and osteomalacia.

Iron
found in both meat and plants. its needed for haemoglobin in red blood cells. deficiency leads to anaemia

Metabolic Pathways

2007-10-14T09:00:00.000-07:00

Metabolism
This is the sum total of all the reactions occurring in the cells.
reactions include the breakdown of glucose to CO2 and H2O.
These reaction take place in a series of steps e.g reactants----- intermediates-----products
Each reaction in a pathways is catalysed by an enzyme.
The products can act as an inhibitor of an enzyme so it can control its own production.

Catabolism: the breakdown of complex molecules into smaller ones e.g. break down of glucose
This usually creates ATP
Anabolism: the synthesis of complex molecules from simple ones. e.g. joining amino acids together.
this usually uses ATP

The cell has two ways of controlling metabolic reaction:
1) compartmentalisation e.g. reactions take place in specific areas of the cell
2) enzymes, which can be inhibited by their products.

OXIDOREDUCTASES catalyse oxidation and reduction
HYDROLASES catalyse hydrolysis reactions e.g. breaking molecules byt he addition of water. used in : digestion etc

cellular respiration

All living organisms require energy for three major reasons:

1) for mechanical work e.g. muscle contraction

2) the active transport of ions across cell membranes

3) the synthesis of macromolecules

This 'free' energy is obtained from the environment.

Cellular respiration is the oxidation of food substances to obtain 'free' energy. Free energy can be used to drive reaction that require an input of free energy, such as active transport.

It occurs as a series of linked, enzymes catalysed reactions.

1) Gylcolysis

2) Krebs cycle

3) oxidative phosphorylation

Atp- Adenosine Triphosphate
this is the most important product of cellular respiration.
Used at an immediate source of free energy rather than a long term store. Its rate of production is high and usually used with 1 minute of synthesis.

adenosine-ribose(5 carbon sugar)-3 inorganic phosphate groups

This is important because the phosphoanhydride bonds yield a high amount of free energy when hydrolysed.Atp can be hydrolysed to ADP (adenosine diphosphate) and Pi and hydrogen.

ATP+ H2O---> ADP + P(i) + H(+)

deltaG= -30 kj mol-1

This is an exergonic reaction as it yields free energy.

ATP is quickly resynthesised from the products when food substances are oxidised in chemotropic organisms or due to light trapping on photosynthetic organisms.

Electron Carries

Many reactions in metabolic pathways require the removal of electrons or hydrogen atoms in the oxidation of substrates.

The electrons are transferred to a group of substances known as electron carriers (aka coenzymes or hydrogen carriers)

The reduced form of these carries transfer their electrons to oxygen by a chain of electron carriers in the inner mitochondrial membrane. ATP is formed from ADP and Pi as a result.

NAD(+) = Nicotinamide adenine dinucleotide.

when a substrate is oxidised NAD accepts a hydrogen ion and 2 electrons. the reduced form is NADH. only 1 hydrogen atom is passed on

NAD(+) + 2H(+) + 2e(-) ----> NADH + H(+)

overview:

1) Intake of Food substances

2) substrate oxidised (oxidation removes hydrogen and electrons)

3)NAD(+)---reduced by addition of hydrogen and electrons to NADH

4)These reduced forms transfer their electrons to oxygen in the inner mitochondrial membrane

5) ATP is produced as a result of the energy released in the process below. the energy is used to generate another process in the cell to make atp.

(2NADH + 2H+ + O2 ==> 2NAD+ + 2H2O) dont have to learn!

Glycolysis

This occurs in the cytoplasm of cells and is a series of enzyme-catalysed reactions in which each molecule of glucose is turned into 2 molecules of pyruvate.

Pyruvate: a compound containing 3 carbon atoms and links glycolysis to the next reaction.

glucose + ATP ------(hexokinase)-------> glucose 6-phosphate + ADP + H(+)

Phosporylation of glucose:

1)prevents glucose from leaving the cell, as the membrane is impermeable to sugar phosphates.

2) it makes glucose more reactive

summary:

Two 3-carbon compounds of Pyruvate are made from each molecule of glucose.

2 molecules of ATP used but 4 produced in glycolysis.

NET PRODUCTION :TWO MOLECUlES OF ATP

Pyruvate then passes into a mitochondrion and then the krebs cycle occurs.

Aerobic Respiration(oxygen present)

The krebs cycle

Pyruvate created in glycolysis passes into the matrix of a mitochondrion. The link reaction now occurs, where Pyruvate is turned into acetate and added to coenzynme A, forming ACETYL COENZYME A. Also NADH is formed and CO2.

Pyruvate + NAD(+) + CoA ---------> Acetyl CoA + NADH + CO2

4 carbon compound combines with with two carbon acetyl to form acetyl CoA, this forms a 6 carbon compound citrate.

2 atoms are lost in each turn of the cycle. These are lost as CO2.

NAD reduced and FAD

Hydrogen is lost

summary:

Two carbon atoms enter the carbon cycle and two carbon are lost as carbon dioxide

one molecule of ATP is formed

4 pairs of hydrogen are removed

3 NAD's are reduced and 1 FAD is reduced

The reduced electron carriers are reoxidised in the electron transport chain.

Oxidative Phosphorylation

this is the process by which atp is made. ATP is formed when electrons are transferred from NADH or FADH2 to oxygen.NADH oxidation produces 3 ATP, FADH2 oxidation produces 2 ATP.

Each [H] atom splits into [H+] and [e-]

The transfer of electrons to oxygen through electron carriers leads to [H+] being pumped from the matrix into the inter membrane space. when they flow back into the matrix the free energy made avaliable is used to make ATP.

Electrons are transfered from NADH to oxygen through a series of large protein complexes.

Oxygen acts as the final electron recpetor and is reduced to form the final product which is , water.

ATP YIELD: 36 molecules from one glucose molecule.

Anerobic respiration:

the electron transport chain cannot function without oxygen. Respiring anerobically poses a problem as they need to reoxidise electron carriers.

used during vigorous physical exertion.

Pyruvate is reduced to Lactate and NAD so glycolysis can continue.

lactate accumulates in the muscles and after exercise lactate is oxidised back to pyruvate.

In yeast it ends up with ethanol and CO2 produced, the yield of ATP is two molecules from one molecule of glucose.