STAge 2

Water availability- tolerance limits

Balance between the intracellular and extracellular space

hypertonic, isotonic, hypotonic solutions

Blood glucose level- tolerance limits

Too low = hypoglycaemic

Too high= hyperglycemic

Steroid:

• Diffuse through membrane

• Binds to intracellular receptors

Non-steroid:

• Cannot diffuse through membrane

• Therefore must bind to receptor on cell membrane

Sensory receptors

Detect Stimuli (Changes in internal/external environment)

Effector receptors:

A gland or muscles that carries out response to combat initial stimuli

Peripheral nervous system (PNS)

• Somatic: We control / voluntary = involved in moving skeletal system and muscles

• Autonomic: We don’t control / involuntary = involved with heart rate and gland

Endocrine system

Involves a system of glands that secrete hormones that trigger responses.

Peptide hormones:

Hormones that are made of short polypeptide chains

Protein Hormones:

• Amino acid-based

• Made from longer polypeptide chains

• Tyrosine based

Steroid hormones:

• Fat-based (lipids)

• Insoluble in water

Sensory Neurons

• Type of nerve cell that transmits information from a receptor (cell or tissue that detects stimuli) to CNS

• Longest neuron/dendrites 

• Centred Cell Body

Dendrites:

• Receive signals from sensory receptors from other neurons and transmit towards the cell body    

• Is complementary in shape to the neurotransmitters

Cell body:

Contains the nucleus and many organelles

Axons or axon terminals:

• transmit information to another cell or an effector

• VERY long

• Small swelling at the end, containing neurotransmitters

• Chemicals that transmit messages between neurons or an effector (cell)

Interneurons

• Found in CNS and communicates information from the sensory neuron to the Motor Neuron

• Shorter in length

• Short Axons

Motor neurons

• Transmits the message from the CNS to the Effector (gland or muscle)

• Cell body connected to dendrites

Describe the role of sensory receptors.

Detect the stimuli and relay the information to the motor neurons through interneurons

Describe the role of effectors.

• Effectors (glands or muscles) relay the response from the sensory neurons

Exteroceptor

Detect external stimuli and are found on the skin or near

Interoceptors

Detect internal stimuli from organs and blood vessels

Proprioceptors

Detect Stimuli from skeletal muscle, tendons and ligaments

Explain the stimulus–response model.

Stimulus:

• A variable factor in the internal or external environment that can be detected by an organism through receptors.

Receptor:

• A cell or tissue that identifies and detects changes from the internal or external environment

Response:

• Outcome that occurs because of the initial stimulus

Effector:

• A gland or muscle that causes the response to the stimulus

• Nervous system (endocrine system)

• Hormones

Feedback:

• Impact of the response (POSITIVE OR NEGATIVE)

• Positive: Reinforces stimulus

  • eg, blood clot via platelets

• Negative: Diminishes and stops stimulus

Negative: (COUNTERACT)

Either reverse the stimulus or diminish its effects

Positive:  (ENHANCE)

Reinforces the initial status or increases it

Describe the structure of a nerve pathway from receptor to effector.

• The stimuli is initially detected from either the internal or external environment

• The stimulus is detected by the sensory receptors which then signals to the → sensory neuron, → inter neuron → motor neuron 

• which then signals to an effector (gland or muscle) triggering a response.

Describe the role of adrenaline in the 'fight or flight' response.

The fight or flight response is resulted due to psychological change like stress. Thus, the adrenal gland secretes adrenaline into the bloodstream where it increases ones blood pressure, increase in respiration rate in the lungs and increase in metabolic rate. Additionally, glycogen is broken down into glucose, which is covered into ATP for energy use. 

Explain how a decrease in the pH of the blood would be responded to by the nervous system.

When a decrease in pH of the blood is evident, this means that the concentration of carbon dioxide is greater than oxygen. Carbon dioxide crosses the blood brain barrier into the ceribal spinal fluids. Carbon dioxide combined with water to create carbonic acid. The carbonic acid is dissociates into H+ ions and hydrogen carbonate. The H+ ions bind to the receptors of the medulla oblogata, where is sends a electrical impulse to the diaphram telling it to respire more. As a result, oxygen is breathed in and carbon dioxide is expelled, returning the pH back to its optiumum pH. 

Synapse

• Synapses are the small space between an axon and dendrites 

axon connects to dendrites

Neurotransmitters:

Chemicals that bind to receptors in the synapses and either transmit a message or stimulate a response

How does a reflex response differ from a regular response?

• Reflex = faster response

Unconscious response NOT involving brain

How hormones stimulate responses: Protein and peptide hormones

• Polar (water soluble) = do not travel into cell directly

• Actions occur as a result of binding to target cell membranes that possess complementary receptors to the hormones

How hormones stimulate responses: Steroid hormones

• Non-polar (lipid soluble) and travelling directly into the cell

• Bind to internal receptors

high blood glucose levels

• b pancreatic cells secrete insulin into blood stream

• insulin binds to receptors on liver and fat cells increasing glucose uptake

• liver cells converts glucose to glycogen

• reduction in blood glucose

low blood glucose

• a pancreatic cells secrete glucagon into bloodstream

• glucagon binds to receptors on liver cells.

• convert glycogen to glucose

• increase blood glucose

Hormonal balance:

• Insulin and glucagon work in balance to maintain homeostasis in animals

• When the two are NOT balanced = DIABETES (diabetes mellitus)

• Diabetes causes harm in animals as organisms lack insulin to regulate the amounts of sugar in the bloodstream.

Symptoms of diabetes:

• Frequent Urination: body’s attempt to clear glucose to not overwork the kidneys

• Thirsty: body uses water to expel excess glucose. This increases thirst levels as water is lost

• Hungry: can not absorb glucose in the bloodstream, and cells are drained of energy to signal to continue eating.

Type 1 diabetes

• Genetically inherited

• Unable to produce insulin

• The immune system does not recognise healthy cells and destroys insulin-producing cells in the pancreas

Type 2 diabetes

• Diet-based

• No longer respond to insulin

high body temp- nervous

• change in temp detected by thermoreceptors in hypothalamus

• transmission: near skin

• sweating: cools skin upon evaporation

• vasodilation: increase heat loss by widening blood vessels.

low body temp- nervous

• change in temp detected by thermoreceptors in hypothalamus

• transmission: near skin

• shivering: muscles contract to produce heat

• vasoconstriction: reduce heat loss from skin by narrowing blood vessels

low body temp- endocrine

• change in temp detected by thermoreceptors in hypothalamus

• stimulates pituitary gland to secrete TSH into bloodstream

• TSH binds to receptors of thyroid

• thyroid secretes thyroxine into bloodstream

• increase metabolic rate + increase body temp

high body temp- endocrine

• inhibits pituitary gland

• no secretion of TSH

• Thyroid reduces secretion of thyroxine

increase osmolarity (define)

• increase solute concentration

• decrease water concentration

decrease osmolarity (define)

• decrease solute concentration

• increase water concentration

high blood osmolarity

• change detected by osmoreceptors on hypothalamus

• stimulates pituitary gland to secrete ADH into bloodstream

• ADH binds to kidney receptors on the collecting ducts on nephrons

• promotes insertion of aquaporins into collecting duct membrane

• allows greater water reabsorption into blood stream

• decrease water in urine + increase BP and BV

• decreases blood osmolarity

• urine is more concentrated

low blood osmolarity

• change detected by osmoreceptors on hypothalamus

• inhibits pituitary gland from secreting ADH into bloodstream

• permeability of collecting ducts decreases 

• less aquaporins are inserted into membrane

• decrease water reabsorbed into bloodstream

• blood osmolarity increases

• decrease BP and BV

Explain why drinking alcohol at a social event leads to dehydration.

Drinkign alcohol inhibits the pituitary gland, meaning ADH can not be secreted in the bloodstream onto the kidney. A decrease in ADH means less aquaporins are present in the collecting ducts on the nephron. This means less water is reabsorbed into the bloodstream and more water is excreted out. 

Explain why drinking alcohol at a social event could also raise blood pressure.

Drinking alcohol can raise ones blood pressure due to vasoconstriction. As the blood vessels are constricted, a decrease in heat loss is exhibited but also an increase in blood pressure due to the constriction.

RNA- Pre-historic evidence

• First genetic material

• RNA is thought to have existed before DNA, either single or double stranded.

• Ribozymes act as enzymes but are made of RNA

• The suggested role of ribozymes in first cells was to catalyse chemical reactions such as RNA replication.

Comparative genomics:

• Relies on the fact that mutations accumulate over time and the rate of mutation is relatively constant over time. 

• The Longer two organisms have been separated from common ancestor = greater No. of differences in DNA (gene) in corresponding proteins.

Comparative genomics reasoning:

• Organisms have common features attributable to commonly shared sequences of DNA

• Similar in function = similar in proteins (e.g. enzymes) between species

• Similar proteins = similar DNA sequences (genes)

• Similarities between different organisms= similarities in DNA and protein molecules.

DNA sequencing

• Comparing two DNA sequences to one another and the differences between them. 

• These differences could be from point mutations (insertions, deletions or substitution).

  • greater accumilations of mutation = CA diverged longger ago)

• Mutations in the DNA would have accumulated over time

Common Protein sequencing

• See the difference between 2 different amino acid sequences from same protein

• It only works if there is a common protein between all species 

  • Species that you're looking at. 

• Cytochrome c is a protein that is necessary for the aerobic respiration pathway in almost all living organisms. 

  • This makes cytochrome C an excellent protein to analyse for identifying evolutionary relationships.

• Different species produce proteins with very similar amino acid sequences = infer that their DNA is very similar (inherited from common ancestor)

DNA HYBRIDISATION (mechanics)

• Takes samples of DNA from different organisms and recombines to see how effectively they bind together.

• If bound together, they need to be reheated to identify DNA melting point of recombinant DNA

• High melting point: similar (closer to CA)

• Low melting point: different (diverged from CA)

DNA HYBRIDISATION LIMITATIONS

• More time consuming (labour intensive)

• outdated

• Subject to more errors

• Bacterial genetic analysis

• Can’t guarantee hybrid DNA formation

• Not comparing individual base differences

DNA HYBRIDISATION STEPS

1. A gene sequence from two species is isolated using a gene probe and restriction enzymes. (act as pair of biological scissors)

2. The DNA of the two species is then heated to 95 degrees

3. The heated strands are then mixed together and allowed to cool down. 

4. The cooling down allows Species A and B DNA mixed together the DNA hybrid to form.

5. The new hybrid DNA is then heated again to work out the melting point, which will identify how similar the two species

Species:

Species are a group of organisms that share:

• Physical characteristics

• Can exchange genes

• Interbreed to produce FERTILE offspring

• Additionally species look similar, are biochemically similar and share a common gene pool

• Species can be defined by:

  • Morphological similarity: The way they look

  • Biochemical similarity

  • Sharing a common gene pool.

PRE-ZYGOTIC reproductive isolation mechanisms

OCCURS BEFORE THE ZYGOTE FORMS

• Temporal isolation

Species remain isolated as their mating seasons occur at different times

• Behavioural isolation

  • Species remain isolated as their Courting process and mating behaviour are different

• Mechanical/Chemical isolation

  • Species remain Isolate as there are Structural and Chemical barriers stopping fertilisation

• Gamete isolation

  • Species remain isolated as proteins on the surface of the egg stop incorrect sperm

POST-ZYGOTIC reproductive isolation mechanism

OCCURS AFTER THE ZYGOTE FORMS

• Hybrid Sterility

  • Two species breed

  • Offspring is unable to undergo Meiotic cell division and is infertile

  • Cannot contribute to the Gene Pool

• Hybrid inviability

  • Two species breed

  • Their offspring is born weak and is unable to reach maturity

  • Cannot contribute to the Gene Pool

Variation in the meiosis process:

• Crossing over

• Independent assortment

• Random fertilisation

Genetic Variation

The extent of genetic variation will differ depending on whether the species reproduces by sexual or asexual means.

ASEXUAL - variation can only occur via mutations

SEXUAL - variation is occurs by

• Mutations

• Random Fertilisation

• Crossing over (prophase 1)

• Independent assortment (metaphase 1)

Gene pool:

• A population is the sum of all the alleles (of all the genes) of all in the individuals in a populations

• All genetic information across all individual organisms

• Within a gene pool various alleles and allele frequencies influence variation

• increase gene pool = increase genetic variation

• increase gene pool = increase chnace of overcoming selection pressures

Mutations

• Occurs in DNA of organism

• Changes in an organism's DNA can give rise to new allelic forms of genes. 

• Only if the changes are in the germ line will they be inherited by their offspring

• If mutation occurs and its inheritable, an offspring will have this new mutation

• Selection pressures influence the outcome the mutation has in gene pool

Gene Flow

• Gene flow occurs between two populations of the same species

• It is the exchange of alleles between populations 

• Occurs when an individual from one populations move to another, 

  • sharing genes INTO the gene pool

• Increased gene flow keeps two population from differing

• increse gene flow = decrease differeing

• decrease gene flow = increase differing

Genetic Drift

• Change in the allele frequency of brought from random sampling:

• Allele frequency is the proportion of individuals carrying a particular allele in a population

• Caused by two mechanisms

  • Bottleneck effect  

  • Founders effect

Bottleneck effect

A reduction in population size which causes a drastic change in allele frequency

• This leads to an over representation of certain alleles in the population

Founders effect

One population migrates to a new isolated geographical area

• contributing to the gene pool in that area

These new individuals make up the gene pool and may be a non-random representation of the original population

• In the new habitat with different proportions of alleles

• cant provide favourable alleles

• decrease gene pool, increase change of selection pressures

Selection pressure

The environmental selection pressures will determine the success of a group, rather than the group ‘adapting’ to the conditions

Biotic

• Predators

• Diseases

• Competition with other organisms 

Abiotic 

• Weather Changes

• Rainfall 

• Temperatures

• Light intensity

• Overuse of medication 

  • (humans)

Natural selection steps

1. There is a high degree of genetic variation and allele frequency within the populations

2. Selection pressures act on population those individuals with favourable alleles survive

3. Therefore they have a higher chance of sexual reproduction and offspring inheriting favourable characteristics

4.  As individuals with favourable characteristics continue to survive and reproduce, the frequency of the favourable characteristics increases, eventually becoming a permanent adaptation.

Speciation:

The evolutionary process by which populations evolve to become new and distinct.

ALOPATRIC SPECIATION

• occurs when populations of a species become geographically isolated.

1. Geographical isolation of the original population

• Isolation of a population means the separated populations cannot share Gene pool

• Isolation into separate populations occurs via geographic barriers

• Isolation prevents gene flow throughout the population, stopping any differences in one population from reaching the other population

• The isolated populations are now subjected to different environments and selection pressure

2. Time is needed for new Alleles to arise by mutation

• Any new alleles that arise by mutation in one isolated population cannot spread to the other isolated population

• Beneficial mutations increase the variation in the gene pool of the different populations

• Variation is necessary for natural selection

3. Time is needed for natural selection to occur

• Now isolated by geographical barriers, natural selection selects those individuals best adapted to the different environments

• Over time the isolated populations begin to evolve different characteristics and different gene pools

• Eventually the populations will be so different that they will not be able to interbreed even if isolation stops. They are then different species

Over time, the morphology of the Kakapo has become extremely specialised. In particular, its beak has become adapted to the food available on land, comprising the tips of high rimu branches, juicy supplejack vines and orchard tubers grubbed out of the ground.

Discuss the effect of specialisation Kakapo on the size of its gene pool, and how this may be impacted by the reduced availability of their preferred food source, owing to climate change and human impacts.

A high degree of specialisation may indicate that these differentiated species would have to adapt to the food avaliability, which takes time through an accumilation of mutations. However, due to anthropogenic sources which contribute to climate change and deforestation, the species would need to adapt to the changes. However, with a smaller gene pool due to specialisation, selection pressures are more likley to act on the species, thus are more prone to extinction. 

SYNPATRIC SPECIATION:

• share same habitat, but reproductively isolated

Divergent Evolution

• recent common ancestor

• produce homologous structures

• each group is separated 

  • exposed to different selection pressures

• differences in geonomes

  • mutations

  • no gene flow

  • speciation occurs

• slow

adaptive radiation

• one splitting into a lot

• rapid divergence

Convergent evolution

• differen species develop similar features

• different common ancestor

• analogous structures

• if different

  • similar habitat = similar selection pressures

    • therefore: similar structures/behaviours

homologous structures

• divergent

• similar internal anatomy = different function

• from CA

analagous

• convergent

• similar function different structure

Primary succession

Starts UN-INHABITAL

1. It begins as a Pioneer species arrives and reshapes the land, breaking down rock into soil and adding nutrients to the soil. 

2. Spores from small plants that can grow quickly inhabit the area and then slowly over long periods of time larger and more complex species can inhabit the area.

Secondary Succession

A previously inhabited land has been wiped clean by a bush fire or other disaster.

1. Regrowth in this area is fast as the soil is nutrient rich due to all of the dead organic matter.

2. This results in opportunistic species to inhabit the area first and then eventually more complex and larger species will arrive over time.

Succession Productivity

• Productivity: the rate of which biomass is formed. 

• This would involve the use of nutrients to form organic life.

• In secondary succession the pioneer phase is the most productive as the pioneer species grow rapidly.

Niches

An environmental role an organism occupies in a community. 

• Organisms physical and environmental conditions 

• Habitat, food sources, water sources, etc

bio-accumilation

• chemicals released into environment

•  NOT excreted.

• biomagnification: organisms in high trophic levels accumulate increase amounts of chemicals

TRANSCRIPTION

• RNA polymerase attaches to the promoter region of the template strand separating the strands by breaking the weak hydrogen bonds. 

• RNA polymerase attaches RNA nucleotides to their complementary counterpart on the template strand. 

• Synthesis continues until RNA polymerase reaches the terminator region and detaches. 

The 5’ to 3’ pre-mRNA copy of the coding strand exits to the cytosol via nuclear pores.

Coding Strand:

has same sequence as the mRNA produced during transcription but thymine is replaced with uracil 

Template Strand:

The strand in which RNA polymerase is used as a guide to synthesize mRNA.

TRANSLATION

1. Translational mRNA enters the cytosol

2. Small ribosomal subunits (SRS) bind to the start codon. SRS attracts the large ribosomal subunit to form the ribosomal complex. 

3. Ribosomes read each codon on the mRNA in a 5’ to 3’ direction, attracting the tRNA with complementary anticodon to bind. 

4. tRNA releases the associated amino acid in the ribosomal complex binding each together with a peptide bond growing into a chain (polypeptide chain). 

Translation continues until the ribosome reaches the release factor bound to stop codons dissociating and releasing a full polypeptide chain.

Anabolic

Aligns substrate in the active site with correct orientation to support synthesis of new bonds

Proto Oncogenes:

• Promoting cell division, yet if uncontrollable, it can lead to cancer formation.

• Acetylation and Demethylation will cause an over production of Proto Oncogenes

• Cells with errors in DNA will be allowed to divide uncontrollably = Cancer formation 

Tumor Suppressor:

• Slows down cell division (definition of cancer is uncontrolled cell division) 

• Hyper-methylation and deacetylation will prevent expression of Tumor suppressor gene 

• Increased DNA methylation on tumor suppressor genes will switch them off, and proteins suppressing tumor formation can no longer be produced.

Point mutation:

One base change

Silent Mutation

alters codon corresponding to same amino acid (e.g. GUA [Val] is changed to GUU [Val])

Missense mutation

Changes the amino acid sequence, altering codon coding for different amino acid

Nonsense Mutation

1. Changes the amino acid to code for a STOP

• Shortens polypeptide chain

PCR (needs + purpose_

PCR enables single copy of a gene to be amplified (REPLICATED)

Called thermal cyclers

To perform a PCR, it must meet the requirements:

• DNA Sample

• Free DNA nucleotides

• 2 Primers complementary to the ends of the region to be amplified (replicated)

• Thermostable DNA polymerase, otherwise it will denature

• A PCR machine (no shit)

• Buffer

Describe PCR STEPS (IN THE TEST)

Step 1 (denaturation): Heating and Cooling

• A DNA molecule is denatured by heating a reaction mix to 95° to break weak hydrogen bonds between base pairs.

• Destroy weak hydrogen bonds between bases

Step 2 (annealing): Primers 

• When temp is 55°, primers are added

• Cooling to 55° to allow primers to bind by complementary base pairing to the start of the target DNA strands to guide DNA polymerase synthesis

• 5’ to 3’

Step 3 (extension): Free nucleotides

• When temp is raised to 72° and the thermostable DNA polymerase and free DNA nucleotides are added to start the replication process: synthesis of new DNA

• This is optimum temp

Primers

• Primers act as the prompt region to allow for DNA polymerase to bind to the site.

• Short stretches of nucleotides complementary bind to the ends of the opposite strands of the regions to be amplified.

• Two primers are needed for PCR. Become part of new DNA

Usually 18-20 nucleotides (unique and specific) are long and bind to the target DNA.

Heat-resistant enzymes

• hermostable DNA polymerase is a heat resistant enzyme that builds new strands, complementary to single stranded DNA of templates.

• ‘Heat resistant’ = no Denature at high temps

Steps of Electrophoresis:

Creating Gel

• Agarose and buffer are mixed together and microwaved to create a gel. 

• Gel is poured into mold and has a ‘comb’ placed into it to make wells. 

• When cooled, the comb is removed to leave wells where DNA fragments can be placed.

Preparing for Electrophoresis

• Gel is placed in electrophoresis box and buffer solution is added

• Buffer solution provides ions to conduct electrical current

Restriction enzymes

• Restriction enzymes must be used to cut DNA into different sized pieces

Inserting DNA samples

• DNA samples are inserted into wells using micropipette

Marker DNA

• DNA fragments of a known size are put into one well (Marker DNA) 

• Marker DNA is used as a ruler

*****

• Electrical current is turned on

• Negative charge on DNA is attracted to positive electrode (Anode)

• Smaller DNA fragments = Further passes through Gel

Using UV light

• After Electrophoresis, DNA in gel is stained

• Expose to UV Light = Stained DNA fluorescence makes bands visible.