The document summarizes nervous and hormonal communication in the human body. It discusses how receptors detect stimuli and send signals via neurons in the nervous system or hormones in the bloodstream to effectors that produce a response. It describes the structure and function of neurons, synapses, and receptors in detail. It also explains muscle contraction and the control of heart rate.

1. Biology
Unit 5
AQA

2. Nervous & Hormonal
Communication
 Receptors detect stimuli and effectors produce a response:
◦ Receptors can be cells or proteins on cell surface membranes
◦ Effectors include muscle cells & cells found in glands
 Nervous system sends information as electrical impulses:
◦ Sensory Neurone – Transmits impulses from receptor to CNS
◦ Motor Neurone – Transmits impulses from CNS to effector
◦ Relay Neurone – Transmits impulses between Sensory & Motor Neurones
 Stimulus Receptor CNS Effector Response
 Peripheral Nervous System:
◦ Made up of neurones that connect CNS to rest of body
 Somatic Nervous System:
◦ Controls conscious activities e.g. running
 Autonomic Nervous System:
◦ Controls unconscious activities e.g. digestion
◦ Sympathetic: - stimulates effectors/speeds things up
◦ Parasympathetic: - inhibits effectors/slows things down

3. Nervous & Hormonal
Communication
 Hormonal system is made up of glands & hormones:
◦ Group of specialised cells that secrete a useful substance
◦ Hormones are ‘chemical messengers’ mostly proteins or peptides
 Glands stimulated by:
◦ Change in concentration of a specific substance
◦ Electrical impulse
 Hormones diffuse directly into the blood
 Hormones usually trigger a response in the target cells

4.  They’re specific to one particular stimulus
 They can be cells, or proteins on cell surface membranes
 How they work:
◦ When nervous system receptor at resting state there’s a difference in
voltage between inside & outside of cell
◦ Resting potential is when a cell is at rest
◦ When a stimulus is detected, cell membrane becomes excited & more
permeable. This allows ions to move in & out of cell.
◦ This alters the potential difference (PD) of cell
◦ Change in PD is called the generator potential (GP)
◦ Bigger stimulus = more ion movement = bigger GP
◦ If the GP is big enough & reaches threshold, a AP is produced
Receptors

5. Receptors in Skin & Eye
 Pacinian Corpuscles – Pressure Receptor in Skin:
◦ They’re mechanoreceptors – detect mechanical stimuli e.g. pressure &
vibrations
◦ Contain the end of a sensory neurone – a sensory nerve ending
◦ Ending wrapped in layers of connective tissue – lamellae
◦ When stimulated the lamellae are deformed & press on the sensory nerve
ending
◦ This deforms the stretch-mediated Na+ channels in the sensory neurone’s
cell membrane
◦ Allows Na+ to move into the cell creating a GP
◦ If the GP reaches the threshold then an AP is produced
 Photoreceptors – Light Receptors in Eye:
◦ Light enters through pupil – amount of light let through controlled by iris
muscles
◦ Light rays are focused onto the retina by the lens
◦ Retina contains the photoreceptor cells
◦ Fovea - lots of photoreceptor cells

6. Receptors in Eye
 Photoreceptors convert light to an electrical impulse:
◦ Light enters eye, hits photoreceptors & absorbed by light-sensitive
pigments
◦ Light bleaches pigments, causes chemical change – membrane more
permeable to sodium
◦ If GP reaches threshold an AP is produced & is sent down the bipolar
neurone
◦ Bipolar neurones connect photoreceptors to the optic nerve
◦ Two type of photoreceptor:
 Rods – Found in peripheral part of retina
– Give information in black & white
 Cones – Found packed together in fovea
– Three types of cone – red, green & blue sensitive
◦ Sensitivity:
 Rods very sensitive to light. Many rods join one neurone, so many weak GP’s combine to reach
threshold and trigger an AP
 Cones less sensitive to light. One cone joins one neurone, so more light is needed to reach the
threshold
◦ Visual Acuity:
 Rods have low visual acuity, many rods join one neurone. This means light from two objects
close together can’t be told apart
 Cones have high visual acuity because each cone joins one neurone and the cones are tightly

7. Neurones
 Resting potential – difference in voltage across the membrane when at rest
 Resting potential maintained & created by Na+/K+ Pumps & K+ Channels
 Stimulus:
◦ Bigger stimulus fires more frequently
◦ Causes Na+ channels to open
◦ Membrane more permeable to Na+
◦ Na+ diffuses into neurone
◦ Inside of neurone more negative
 Depolarisation:
◦ If PD reaches -55mV (threshold), more Na+ open
◦ More Na+ diffuses into neurone
 Repolarisation:
◦ At +30mV Na+ channels close and K+ open
◦ K+ diffuse out of neurone
 Hyperpolarisation:
◦ K+ slow to close
◦ Too many K+ diffuse out of neurone
◦ More –ve than resting potential
 Resting Potential:
◦ Na+- K+ pump returns membrane to rest
 Refractory Period:
◦ Makes sure no overlaps or travel in one direction
K+ OpenNa+ Close
Threshold
Na+ Open
K+ Close
Refractory Period

8. Factors Affecting Speed of Impulse
 Myelination:
◦ Some neurones have a myelin sheath – electrical insulator
◦ Made up of Schwann cells
◦ Between Schwann cells are nodes of Ranvier
◦ Neurone’s cytoplasm conducts enough electrical charge to depolarise
next node
◦ Impulse ‘jumps’ from node to node – saltatory conduction
 Axon Diameter:
◦ Faster with larger diameters – less resistance
◦ Depolarisation reaches other parts of neurone quicker
 Temperature:
◦ Ions diffuse faster at higher temperature
◦ Up to 40°C – after that the proteins denature
Motor Neurone
Sensory Neurone
Myelinated Axon
Dendrites
Cell Body
Motor End Plate

9. Synapses
 Presynaptic neurone has a swelling – ‘synaptic knob’
 Synaptic knob contains vesicles – filled with neurotransmitter
 When AP reaches end of neurone causes neurotransmitter to be
released into synaptic cleft
 Neurotransmitter diffuses across cleft & binds to receptor
 Triggers AP, Muscle Contraction or Hormone Secretion
 Neurotransmitter removed from receptor by enzymes
 Cholinergic Synapse:
◦ AP arrives at knob
◦ Stimulates voltage-gated Na+ channels to open
◦ Ca2+ diffuse into knob
◦ Causes vesicles to fuse with presynaptic membrane
◦ Vesicles release ACh (Acetyl Choline) in cleft – exocytosis
◦ ACh binds to specific receptors on postsynaptic membrane
◦ Na+ channels open on postsynaptic membrane
◦ Na+ influx produces an AP
◦ ACh removed from receptor by AChE and reabsorbed into presynaptic membrane

10. More Synapses
 Neuromuscular Junction:
◦ Synapse between motor neurone & muscle cell
◦ Similar to cholinergic synapse, but a few differences
◦ Post-synaptic membrane has lots of folds forming clefts, containing AChE
◦ Post-synaptic membrane has more receptors
◦ AP from motor neurone always triggers a response in a muscle cell
 Neurotransmitter are Excitatory or Inhibitory:
◦ Excitatory depolarise the post-synaptic membrane, making it fire an AP if threshold is
reached e.g. ACh
◦ Inhibitory hyperpolarise the post-synaptic membrane preventing an AP being fired
e.g. GABA
 Summation:
◦ Effect of neurotransmitter released from many neurones is added together
◦ Spatial:
 Many neurones connect to one neurones
 Small amount of neurotransmitter from each can be enough to reach threshold &
produce AP
 If some release inhibitory neurotransmitter then total effect might not produce an
AP
◦ Temporal
 Two or more impulses arrive in quick succession from same pre-synaptic neurone

11. Drugs Affecting Action of
Neurotransmitter
 Same shape as neurotransmitter, mimic their action so more
receptors are activated
 Block receptors so they can’t be activated by neurotransmitter, less
receptors activated
 Inhibit enzyme that breaks down neurotransmitter, receptor is
blocked by neurotransmitter
 Stimulate release of neurotransmitter from pre-synaptic membrane
 Inhibit release of neurotransmitter from pre-synaptic membrane

12. Muscles
 Skeletal muscles (striated, striped or voluntary muscles)
 Made up of muscle fibres
 Cell membrane of muscle fibre cells is the Sarcolemma
 Bits of sarcolemma fold inwards across the muscle fibre and stick into the
sarcoplasm (muscle cell’s cytoplasm)
 These folds are called transverse (T) tubules & help spread impulses throughout
sarcoplasm
 Network of internal membranes called Sarcoplasmic Reticulum
 Sarcoplasmic reticulum stores Ca2+ needed for muscle contraction
 Muscle fibres are multinucleate (contain many nuclei)
 Muscle fibres have lots of long, cylindrical organelles called Myofibrils
 Myofibrils:
◦ Contain thick & thin filaments
◦ Thick = made of myosin
◦ Thin = made of actin

13. Muscle Contraction
 Myosin has globular heads
 With a binding site for ATP & actin
 Tropomyosin & troponin found between actin filaments, helps filaments slide
over each other
 At rest actin-myosin binding site blocked by tropomyosin, held in place by
troponin
 AP depolarises sarcolemma, spreading down T tubules to sarcoplasmic
reticulum
 Sarcoplasmic reticulum releases Ca2+ into sarcoplasm
 Ca2+ binds to troponin causing it’s change shape
 Pulls tropomyosin out of actin-myosin binding site, exposing site
 Bond between myosin head & actin creating a actin-myosin cross bridge
 Ca2+ also activates ATPase, providing energy
 Energy released moves myosin head, pulling actin molecule
 ATP provides energy to break cross bridge
 Myosin head reattaches to different binding site, creating new cross bridge
 When excitation stops Ca2+ leave binding site on troponin & moves into
sarcoplasmic reticulum by AT

14. More Muscle Contraction
 Aerobic Respiration:
◦ Most ATP produced via oxidative phosphorylation in mitochondria
◦ Long periods of low-intensity exercise
 Anaerobic Respiration:
◦ ATP made rapidly by glycolysis
◦ Produces pyruvate which converts into lactate
◦ Lactate builds up in muscles causing fatigue
◦ Short periods of high-intensity exercise
 ATP-Phosphocreatine (PCr) System:
◦ ATP produced by phosphorylating ADP, adding a phosphate group from PCr
◦ PCr stored inside cells
◦ Quick production of ATP
◦ PCr runs out after a few seconds
◦ ATP-PCr is anaerobic & alactic (no lactate formed)
 Slow-Twitch Fibres:
◦ Aerobic – Red Colour – high levels of Myoglobin
 Fast-Twitch Fibres:
◦ Anaerobic – White Colour – low levels of Myoglobin

15. Control of Heart Rate
 SAN generates impulses controlling HR
 Unconsciously controlled by Medulla
 Stimuli are detected by baroreceptors & chemoreceptors:
◦ Baroreceptors in Carotid Arteries – stimulated by Blood Pressure
◦ Chemoreceptors in Carotid Arteries – monitor O2, CO2 & pH in blood
◦ Chemoreceptors detect change in pH
◦ More CO2 = More Carbonic Acid = Lower pH
Stimulus Receptor
Neurone &
Neurotransmitter
Effector Response
High BP
Baroreceptor
Impulse to medulla, along
parasympathetic to SAN
Cardiac
Muscle
HR slows BP
lowers
Low BP
Impulse to medulla, along
sympathetic to SAN
HR increases BP
increases
Low CO2
Chemoreceptor
Impulse to medulla, along
parasympathetic to SAN
HR slows CO2 level
returns to norm
High CO2
Impulse to medulla, along
sympathetic to SAN
HR increases CO2
level returns to
norm

16. Reflexes
 Involuntary rapid response to a stimuli
 Thermoreceptors in skin detect heat stimulus
 Sensory neurone carries impulse to Relay
 Relay to Motor
 Motor sends impulse to effector (e.g. biceps)
 Effector muscle contracts stopping hand being damaged
 If relay neurone involved you can override the reflex e.g. leave your
hand on the heat

17. Responses in Animals
 Tactic response (taxes):
◦ Organisms move towards or away from a directional stimulus
◦ Phototaxis – Light
◦ Chemotaxis – Chemicals
◦ Aerotaxis – Air (O2)
◦ Geotaxis - Gravity
 Kinetic response (kineses):
◦ Organisms’ movement is affected by the intensity of the stimulus
 Cells communicate with other cells with Chemical Mediators:
◦ Chemical mediator is a chemical messenger that acts locally
◦ Similar to hormones
◦ Chemical mediators can be secreted from cells not just from glands
◦ Target cells near to where mediator is produced – local response
◦ Only travel a short distance – quicker response
 Histamines:
◦ Stored in mast cells & basophils. Released in response to infection or injury.
Allows more immunity cells to move in & out of blood to the area
 Prostaglandins:
◦ Produced by most cells of the body. Involved in inflammation, fever, BP
regulation & blood clotting

18. Responses in Plants
 Tropism – Plants Growth Response to an External Stimulus
 +ve tropism = growth towards the stimulus
 Phototropism:
◦ Growth in response to Light
◦ Shoot grow towards light +vely phototropic
◦ Roots grow away from light -vely phototropic
 Geotropism:
◦ Growth in response to Light
◦ Shoots are -vely geotropic, grow upwards
◦ Roots are +vely geotropic, grow downwards
 Gibberellin is a growth stimulus flowering & seed germination
 Auxins stimulates growth of shoots by cell elongation
 Auxins inhibit growth in roots
 IAA is an important Auxin – diffuses over short distances & via phloem
over long distances
Root
Root Shoot
Shoot

19. Homeostasis
 Homeostasis involves control systems that keep your internal
environment roughly constant
 Temperature:
◦ If too high enzymes denature, enzymes molecules vibrate, breaks H-bonds, shape of
active site is altered
◦ Optimum - 37°C
 pH:
◦ pH too high or low, enzymes denature
◦ Optimum usually – 7 but specialist enzymes can work higher or lower
 Glucose:
◦ Too high H2O potential of blood is more –ve. H2O moves out of cells by Osmosis
◦ Too low, cells unable to function properly due to lack of energy
 Negative Feedback:
◦ Mechanism that returns the level to normal but only works between certain limits. If
change is too big then effectors may not be able to counteract it
◦ Multiple negative feedback mechanisms give more control
 Positive Feedback:
◦ Mechanism that amplifies the change from the norm, effectors respond to further
increase level away from norm.
◦ Blood Clotting – Platelets become activated – trigger more platelets to be activated

20. Controlling Body Temperature
 Mechanism of Heat Loss:
◦ Vasodilation –arteriole diameter near skin increases – warm blood passes near skin
◦ Increased Sweating – H2O lost by evaporation, body heat used to evaporate H2O
◦ Lowering of Body Hair – less insulating layer – hair erector muscles in skin relax
◦ Behavioural - sheltering in the shade/burrows
 Mechanisms of Heat Gain:
◦ Vasoconstriction – arteriole diameter near skin decreases – blood passes under
insulating fat
◦ Shivering – muscles involuntarily contract – produces metabolic heat
◦ Hairs Stand Up – hair erector muscles contract – traps layer of air next to skin
◦ Hormones – releases adrenaline & thyroxine – increase metabolic rate – more heat
produced
◦ Less Sweating
◦ Behavioural – basking in sun / huddling / sheltering from windEctotherms e.g. reptiles Endotherms e.g. mammals
Control temp by changing their
behaviour
e.g. basking in sun
Control temp internally by homeostasis &
behaviour
Internal temp depends on external
temp
Internal temp less affected by external temp
Activity depends on external temp Activity independent on external temp
Variable metabolic rate High metabolic rate – produces heat

21. Hypothalamus
 Controls body temperature in mammals
 Heat Loss Centre:
◦ Responds to rise in body temp
 Heat Gain Centre:
◦ Responds to fall in body temp
 Receives information about both internal & external temperature
 Information produced by Thermoreceptors
 Internal temperature:
◦ Thermoreceptors in hypothalamus detect blood temperature
 External temperature:
◦ Thermoreceptors in skin detect skin temperature
 Thermoreceptors send impulses to hypothalamus along autonomic
nervous system
 To effectors from hypothalamus along autonomic nervous system

22. Hormonal Control of BGC
 Insulin:
◦ Lowers BGC when too high
◦ Produced by Beta cells in the Islets of Langerhans (pancreas)
◦ Binds to receptors on cell membrane of liver & muscle cells
◦ These cells are more permeable to glucose, cell takes up more glucose
◦ Insulin activates enzyme converts glucose to glycogen
◦ Cells store glycogen in cytoplasm – energy source
◦ Glycogenesis = glucose  glycogen
◦ Insulin increases rate of respiration of glucose, especially in muscle cells
 Glucagon:
◦ Raises BGC when too low
◦ Produced by Alpha cells in Islets of Langerhans (pancreas)
◦ Binds to receptors on membrane of liver cells
◦ Activates enzyme breaks down glycogen into glucose
◦ Glycogenolysis = breaking down glycogen
◦ Gluconeogenesis = forming glucose from non-carbohydrates
◦ Glucagon reduces rate of respiration of glucose in cells
BGC – Blood
Glucose
Concentration

23. Control of BGC
 Adrenaline:
◦ Hormone secreted by adrenal glands
◦ Secreted if BGC is low
◦ Binds to receptors on liver cells
 Activates glycogenolysis – glycogen  glucose
 Inhibits glycogenesis – glucose  glycogen
◦ Activates glucagon secretion
◦ Inhibits insulin secretion
◦ Adrenaline & Glucagon bind to receptors activating Adenylate Cyclase
(enzyme)
◦ This enzyme converts ATP into a chemical signal a ‘second messenger’
◦ Second messenger is Cyclic AMP (cAMP)
◦ cAMP activates a chain of reactions breaking down glycogen into glucose
(glycogenolysis)
 Diabetes:
◦ Type 1:
 No insulin produced, BGC stays high – hyperglycaemia, treated with insulin injection
◦ Type 2:
 Don’t produce enough insulin or don’t respond to insulin
 Treated by controlling simple carbohydrate intake

24. Menstrual Cycle
 Lasts 28 days
 Follicle developing in the ovary
 Ovulation – egg being released
 Uterus lining thickens, to support implanted egg
 Corpus luteum develops from follicle remains
 FSH (Follicle-Stimulating Hormone) – stimulates follicle to develop
 LH (Luteinising Hormone) – stimulates ovulation & corpus luteum
development
 FSH & LH from Pituitary Gland
 Oestrogen – Stimulates uterus lining thickening
 Progesterone – maintains uterus lining thickening
 Oestrogen & Progesterone from Ovaries

25. 1. High [FSH] in Blood:
FSH stimulates follicle development
Follicle releases oestrogen
FSH stimulates oestrogen to be
released by ovaries
2. Rising [Oestrogen]:
Oestrogen stimulates uterus lining
thickening
Oestrogen inhibits FSH
3. [Oestrogen] Peaks:
High [oestrogen] stimulates FSH &
LH production
4. LH Surge:
Ovulation stimulated by LH
LH stimulates follicle  corpus
luteum
Corpus luteum releases
progesterone
5. [Progesterone] Rises:
Progesterone inhibits FSH & LH
Maintains uterus thickening
If no embryo implants, corpus
6. Falling [Progesterone]:
FSH & LH increase (not inhibited by
progesterone)
Uterus lining not maintained so it
breaks down - menstruation

26. -VE & +VE Feedback -
Hormones
 Negative Feedback:
 Example One:
◦ FSH stimulates Ovary to release Oestrogen
◦ Oestrogen inhibits release of FSH
After FSH has stimulated Follicle development, -ve feedback keeps [FSH] low, so no more
follicles develop
 Example Two:
◦ LH stimulates Corpus Luteum, which produces Progesterone
◦ Progesterone inhibits release of LH
-ve feedback makes sure no more Follicles develop when Corpus Luteum is developing
Also makes sure Uterus Lining no maintained if no Embryo implants
 Positive Feedback:
 Example:
◦ Oestrogen stimulates Pituitary Gland to release LH
◦ LH stimulates Ovary to release Oestrogen
◦ Oestrogen further stimulates to release LH
High Oestrogen concentration triggers +ve feedback to make Ovulation happen

27. DNA
 It’s a large polymer of repeating Nucleotides.
 G & A Large Bases (Purines)
C & T Small Bases (Pyrimidines)
 A - T, C - G are the complementary pairs
 Small % of DNA are genes, the rest is junk (VNTRS)
used to create a DNA fingerprint
 DNA molecules found inside nucleus, but organelles for
protein synthesis are found in cytoplasm
 DNA too large to move out of nucleus
 Sections are copied into RNA which then moves to
ribosomes
A – Adenine
G – Guanine
C – Cytosine
T (U) – Thymine
(Uracil in RNA)
P – Phosphate Group
S – Sugar
N – Nitrogen Base (Varies)
Gen
e
Loci
Exo
n
Intron
A & T have 2 H bonds
G & C have 3 H bonds

28. RNA – Single Stranded
 Messenger RNA (mRNA):
◦ Made during transcription in the nucleus
◦ Carries genetic information from nucleus to the cytoplasm
 Transfer RNA (tRNA):
◦ Clover-shaped
◦ Every molecule has a specific anticodon at one end
◦ Amino Acid binding site at other end
◦ Found in cytoplasm where it’s involved in translation
DNA mRNA tRNA
Shape
Double Stranded
Helix
Single-Stranded Single-Stranded
Sugar Deoxyribose Ribose Ribose
Bases A T C G A U C G A U C G
Other… 3 Bases = 1 Codon
3 Bases = 1
Codon
3 Bases = Anticodon or
AA Binding Site

29. Protein Synthesis
 Transcription:
 RNA polymerase attaches to DNA double-helix
 H-bonds between helix break
 One strand is template for mRNA copy
 RNA polymerase attaches free RNA nucleotides to template strand
 RNA nucleotides then form mRNA molecule
 RNA polymerase moves along strand of DNA
 H-bonds reform in DNA, back to a double-helix
 Stops making mRNA if reaches a stop signal (specific base sequence)
 mRNA moves out through nuclear pore & attaches to ribosome
 Splicing:
 Pre-mRNA contains Introns & Exons
 Introns are removed during splicing
 In the nucleus
 Only DNA that codes for AA’s remains

30.  Translation:
 mRNA attaches to ribosome & tRNA carries AA to ribosomes
 tRNA anticodon molecule attaches to mRNA codon (specific base sequence)
 2nd tRNA attaches to next mRNA codon
 2 AAs joined by peptide bond
 1st tRNA molecule moves away leaving it’s AA
 3rd tRNA attaches to next codon, it’s AA bonds to previous 2 AAs
 Process continues producing a polypeptide chain until a stop signal on mRNA
 Polypeptide chain moves away from ribosome
Protein Synthesis

31. Genetic Code
 It’s non-overlapping, degenerate & universal
 The genetic code is the sequence of codons in mRNA which code for
AAs
 Each codon is read in sequence, each codon is read separately
 Degenerate:
◦ Some AAs are coded for by more than one base triplet
 Some codons are used to start & stop protein production
 Same codons code for AAs in all organisms

32. Regulation of Transcription &
Translation Transcription Factors:
◦ They move from the cytoplasm into the nucleus
◦ Bind to specific DNA sites near start of target gene
◦ They control the rate of transcription
◦ Activators – increase the rate
◦ Repressors – decrease the rate
 Oestrogen
◦ Binds to an oestrogen receptor and acts as a transcription factor
◦ Forms an oestrogen-oestrogen receptor complex which moves into the nucleus
◦ It binds near the start of the target gene
◦ Complex can act as an activator or a repressor
◦ Depends what type of cell & the target gene
 siRNA (small interfering RNA):
◦ Short, double-stranded RNA molecules
◦ Their bases are complimentary to sections of target gene
◦ Interferes with transcription & translation
◦ Affects translation through RNA interference:
 In cytoplasm, siRNA & proteins bind to target mRNA
 Proteins cut mRNA into sections so it can’t be translated
 Prevents expression of specific genes as translation cannot occur

33. Mutations
 Change in the base sequence of DNA
 Caused by:
◦ Errors during DNA replication
◦ Mutagenic agents
 Substitution:
◦ One base is substituted for another – causes frame shift
 Deletion:
◦ One base is deleted
 But not all mutations affect order of AAs:
◦ Degenerate nature of DNA
◦ Substitution may not affect AA order but deletion always will
 Mutagenic Agents:
◦ UV radiation, Ionising radiation, some chemicals & viruses
◦ Act as a base – chemicals called base analogues can substitute for a base during DNA
replication
◦ Altering bases – some chemicals can delete or alter bases
◦ Changing DNA structure – some radiation can change shape of DNA

34. Genetic Disorders & Cancer
 Hereditary Mutations:
◦ Some mutations can cause genetic disorders
◦ Some mutations can increase risk of developing certain cancers
◦ If a gamete containing a gene mutation is fertilised it becomes a hereditary mutation
 Acquired Mutations:
◦ Mutations that occur after fertilisation
◦ If mutations occur in genes controlling cell division, can cause uncontrollable cell
division
◦ Produces a tumour – mass of abnormal cells
◦ Tumours invade & destroy surrounding tissues are Cancers
◦ Two genes control cell division:
 Tumour-Suppressor Genes – mutation causes protein not to be produced  uncontrollable cell division
 Proto-Oncogenes –mutation causes it to be overactive  cells to divide uncontrollably
Proto-OncogenesTumour-Suppressor Genes

35. Stem Cells
 Able to mature into any body cell
 Stem cells are unspecialised cells
 Stem cells found in embryo and some adult tissues
 Stem cells that can mature into any body cell are totipotent cells
 Totipotent cells only found in early life of embryo
 After this point they lose ability to become any cell
 Totipotent found in plants:
◦ Mature plants have them where they grow e.g. roots & shoots
◦ All plants stem cells are totipotent
◦ Can be used for tissue cultures – cell placed in sterile growth medium – produces new
plant
 Totipotent become specialised because they only translate &
transcribe part of their DNA
◦ Certain genes are expressed others are turned ‘off’

36. Making DNA Fragments
 Using Reverse Transcriptase:
◦ Most cells contain 2 copies of each gene but contain many mRNA copies
◦ Enzyme converts RNA  DNA
◦ DNA produced from RNA is cDNA (complementary DNA)
 Using Restriction Endonucleases:
◦ Enzymes recognise palindromic sequences of nucleotides
◦ DNA sample incubated with the specific restriction endonuclease
◦ Can leave sticky ends allowing the DNA fragment to anneal to another DNA molecule if
they have a complementary base match
 Using PCR (Polymerase Chain Reaction):
◦ Mixture with Primers, DNA sample, Free Nucleotides & DNA Polymerase
◦ Primer – short piece of DNA complementary to bases at start of fragment required
◦ DNA mixture heated to 95°C to break H-bonds in double strand
◦ Cooled to 60°C so primers can anneal to strand
◦ Mixture heated to 72°C so DNA polymerase can work
◦ DNA polymerase forms a new strand complementary to the template strand
◦ Two new copies are formed, one cycle of PCR complete
◦ Cycle starts again
◦ Each PCR cycle doubles the amount of DNA

37. Gene Cloning
 In Vitro:
◦ Where the gene copies are made outside of a living organism using PCR
 In Vivo:
◦ Where the gene copies are made within a living organism
 In Vivo:
◦ Gene Inserted into a Vector:
 DNA fragment inserted into vector DNA
 Vector – something used to transfer DNA into a cell
 Vector DNA cut open using restriction endonuclease
 DNA ligase joins sticky ends of DNA fragment to vector DNA, Ligation
 New combination of bases in DNA – recombinant DNA
◦ Vector Transfers the Gene into Host Cells:
 If a plasmid vector used, host cells won’t easily take in the Plasmid vector & it’s
DNA
 With a bacteriophage vector, it will infect the host bacterium by injecting it’s DNA
into it
 Host cells that take up the vector containing the gene are Transformed
◦ Identifying Transformed Host Cells:
 Marker genes inserted into vector along with gene
 Host cells grown on agar – creates colony of cloned cells
 Marker gene can code for antibiotic resistance – agar contains antibiotic – only
transformed cells with survive
 Can also code for fluorescence – will show up under UV light
Organisms with
altered DNA are
called transformed
organisms
Genetic engineering -
recombinant DNA
technology

38. Genetic Fingerprinting
 Genomes contain repetitive, non-coding DNA sequences
 Number of repeats of a sequence can be compared between
individuals
 Gel Electrophoresis:
◦ PCR is used to make copies of sample
◦ Primers bind to each end of the repeat
◦ Fluorescent tag added to DNA fragments – visible under UV light
◦ DNA mixture placed into a well in the gel
◦ Gel covered in a buffer that conducts electricity
◦ Electric current passed through the gel, DNA moves towards +ve electrode
◦ Small fragments move further
 Used to determine:
◦ Relationships
◦ Variation
◦ Medical Diagnosis
◦ Forensic Science

39. Locating & Sequencing
Genes Look for genes using DNA Probes & Hybridisation:
◦ DNA probes locate gene or see if DNA contains a mutated gene
◦ DNA probes are short strands of DNA, they have a complementary base sequence to
part of the target gene
◦ DNA probe will bind to target gene & can be detected if it is labelled (fluorescent or
radioactive)
◦ DNA sample digested with restriction enzymes & separated by gel electrophoresis
◦ DNA fragments transferred onto a nylon membrane & incubated with labelled DNA
probe
◦ Membrane exposed to UV or X-ray & bands will be visible
 Restriction Mapping:
◦ Restriction enzymes cut labelled DNA into fragments
◦ Gel electrophoresis produces bands
◦ Compare DNA with different restriction enzymes
 Gene Sequencing:
◦ Mixture of DNA template, polymerase, primer, nucleotides & Fluorescently labelled
modified nucleotides
◦ Each tube contains A*, G*, C* or T* & undergoes PCR
◦ Different length fragments produced depending on where the modified fragments bind
to the DNA e.g. ACTACG*, ACTACGATG* in tube with G*

40. DNA Probes in Medical Diagnosis
 They can screen for mutated genes e.g. Sickle-cell Anaemia:
◦ Probe labelled to look for a specific gene
◦ Or Probe used as part of microarray, which can screen many genes at the same time
 DNA Microarray is a glass slide with microscopic spots of different DNA probes attached in rows
 Sample of labelled human DNA washed over the Array
 Any matches with the probes will stick to the array
 Array washed to remove excess DNA
 Array under UV light shows any labelled DNA
 Any spot that fluoresces contains that specific gene
 Results of screening used to decide what treatment to use

41. Gene Therapy
 Involves altering the defective genes inside cell to treat genetic
disorders & cancers
 Depends if it is caused by mutated dominant or double-recessive
alleles
 Allele inserted into cells using a vector
 Somatic Therapy:
◦ Altering the alleles in body cells, particularly ones most affected by disorder
◦ Doesn’t affect sex cells so offspring could still inherit disease
 Germ Line Therapy:
◦ Alters sex cells
◦ Offspring will not be affected by the disease
◦ Illegal at the moment