Topic 3 unit 2 As Snab biology

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Distinguish between a Eukaryotic and Prokaryotic.

Prokaryotic: 10 BACTERIA

  • RIbosome
  • circular DNA
  • cell surface membrane
  • cell wall (peptidogylcon, polysacharide and polypeptide)
  • cytoplasm
  • flagellum-rotates
  • pilli- protein tubes, allow to adhere to surfaces
  • capsule- slime, prevent dehydration and protection
  • plasmid- small circle of DNA
  • infolding of cell surface membrane, site of respiration

No nucleus with envelope.                                                                                         No membrane bound organelles                                                                                 Small                                            

Some features not present- flagellum, pilli, capsule, plasmid

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Distinguish between a Eukaryotic and Prokaryotic.

Eukaryotic: 10- Animal and plant

  • Mitochondion- inner of membrane folded to produce cristae. site of respiration in later stages of anerobic respiration. (matrix)
  • Nucleus- Enclosed by an envelope. two membranes with pores. Contains chromosomes and genes that do the synthesis of protein
  • Nucleolus- dense, makes ribosomes
  • Rough Endoplasmic Reticulum- interconnected membrane bound flattened sacs. Ribosomes attached to surface. proteines made on ribosomes and transported through vesicles
  • Ribosomes- Made of RNA and protein. found free in cytoplasm. site of proetin sythesis
  • Cell surface membrane- plasma, phospholipis bialayer. partially permable barrier. contains proteins
  • Smooth Endoplasmic Reticulum- no ribosomes, makes lipids and steroids
  • Golgi- flattened sacs, fusion of vesicles. modifies proteins and packages them into vesicles. gets smaller and curved
  • Lysososome- digestive enzymes, single membrane. breakdown
  • Centrioles- microtubles, helix tube, form spindle fibres and transport
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Distinguish between a Eukaryotic and Prokaryotic.

Animal Eukaryotic:

  • Nuclaus with envelope
  • membrane bound organelles
  • separate strands of DNA
  • no slime capsule
  • flagella is complex
  • no cell wall
  • medium

Plant Eukaryotic:

  • Nucleus with an envelope
  • membrane bound organelles
  • separate strands of DNA
  • no slime capsule
  • no flagellum
  • CELLULOSE cell wall
  • large
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Protein Transport

1) Transcription of the DNA to mRNA in the nucleus

2) mRNA leaves the nucleas (translation) through nuclear envelope

3) Amino acid made into protein made on the ribosomes of the rough ER

4) Protein moves through vesicle  and go to FUSE with the Golgi apparatus

5) Proteins are modified in the Golgi and then vesicles pinched off contain the modified protein

6) Vesicle fuses with the cell surface membrane releasing the protein through EXOCYTOSIS

Exported out of the cell, Extracellular enzymes (amylase and protease)

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Mammalian Gametes

OVUM- cant move on its own, wafted by oviducts.

Cytoplasm- contains protein and lipid food reserves for developing embreyo

Lysosome- breaks down unwanted structures

Zona pellucida- surrounds the cell, jelly like coating. freezes

SPERM- motile

Tails- allows it to move and swim to the egg, ATP from mitochondiron

passage to the egg- assisted by muscle contraction

Sperm attracted to the egg by chemicals released from it. 

Acrosome- penitrates ovum, release these digestive enzymes which breaks the zona pellucida- type of lysosome 

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Role of meiosis in producing gametes

Produces gametes with half the number or chromosomes HAPLOID. n. 23:

Two homoglogous pairs chromosomes replicate. pair up then separate. Chromatids separate and gametes are formed, each with half the original number or chromosomes

results in haploid cells which are necessary to maintain diploid after fertilisation       Helps create genetic variation among offspring

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Independant assortment

Shuffle existing genetic material- create genetic variation

Completely Random:

Either chromosome from each pair could be in any gamete. Sharing out chromosomes produces genetically variation in gametes.

Depends on the alignment of the chromosomes during the first division

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Crossing over

During the first part of meiotic division the pairs of chromosomes (homologous) line up and may swap part of their genetic material.

The chromatids come into contact with eachother.

At the chiasma- the chromatids break and rejoin, exchanging sections of their DNA, several of these can occur along the length of each pair giving rise to more large amount of variation.

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Ferilisation in Mammalian Gametes

1) sperm reach the ovum and chemicals are released from the cells surrounding the ovum triggering the ACROSOME REACTION

2) the acrosome swells, fusing with the sperm cell surface membrane and digestive enzymes in the acrosome are released

3) The enzymes digest their way through the follicle cells and the Zona pellucida surrounding the ovum.

4) The sperm fuses with the ovum membrane and the sperm nucleus enters the ovum

5) The enzymes are released from the lysosomes in the ovum which thicken the jelly layer preventing sperm from entering

6) The Nuclei of the ovum and sperm fuse

The diploid cell is restored 43 chromosomes- zygote

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Fertilisation in Plants

Double fertilisation

One male gamete fuses with the egg to form a diploid zygote and another male gamete fuses with two polar nuclei to form a triploid endosperm (seed storage)

Pollen grain germinates on the style and a pollen tube grows to the ovary, controlled by the TUBE nucleus. The second nucleus is the GENERATIVE nucleus which divides to form two haploid gametes. one fuses with the polar nuclei and forms endosperm the other fuses with the egg and forms a zygote. Then forms an embreyo. 

Tripoloid cell- divides to form seeds storage tissue.

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The cell cycle

Interphase: cell synthesis, and new cell componants are made (organelles and membranes, DNA) 

G1- Growth and replication of organells

S- synthesis of the DNA

G2- assembly of the spindle fibres

Zygote doesnt undergow interphase at the beginning, it divides withour growing

G1 longest- takes years sometimes. 

Plants- cell division is localised in meristems

Interphase- newly cell grows, cell undergoes its normal function. cell prepares so divides, replicating chromosomes, they start to condense, some organelles increase. Nucleus is dark because of the ribosomes in the nucleolus

Cytokinesis- cell divides. forms 2 daugher cells. 

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DNA in chromosomes

DNA double helix

DNA winds around proteins

DNA and proteins coil to form a chromatin fibre

Chromatin fibre attatches to a protein scaffolding forming loops

folding the protein scaffolding produces the condensed chromosome structure.

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Cell division

End of interphase- enough ornagelles, dna, cytoplasm to form new cells

so shares out DNA and contents (mitosis) then splits

continuous process. Prophase, Metaphase, Anaphase and Telephase                     Prophase: chromosomes becaome shorter thicker, spindles form (opposite side of cells0, nuclkear envelope breaks down

Metaphase: chromosomes line up at equator as pairs and spindles attatch

Anaphase: spindles contracts fulling the sister chromaditids appart by centromere

Telophase: chromosomes decondense nuclear envelope reaooears and nucleolus

Cytoplasmic division: ANIMALS; cell surface membrane constrics around the center and a ring of protein fillaments bound to the inside surface. contract until two new cells. proetins actin and Myosin are responsible for muscle contraction but in PLANTS; golgi vesicles carrying material for a new cell wall move along microtubles and fuse. cell plate developes.

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cut 5mm of root tip of a onion. (mitosis occurs in root)- CARE WHEN CUTTING

Add stain, orcein and acid. (stain to highlight chromosomes and acid to soften tissue)- EYE AND SKIN CARE WITH ACID AND STAIN

Gently break open on a microscope slide and squash carefully (To spread cells so they are one layer thick too see)- CAREFULL NOT TO BREAK GLASS sLIDe

Add more stain and warm, then look at slide. (warm to intensify stain. microscope because the chromosomes are so small)- EYE AND SKIN CARE WITH STAIN AND POTENTION BURNING DUE TO HEAT

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Mitosis in Growth and repair and Asexual reproduct

Ensures genetic consitancey, daughter cells identicle, same number and type of chromosomes.

Dna replication prior to nuclear division and the arrangement of the chromosomes on the spindle and the separation of the chromatids to the poles.

Growth and repair: mitosis occurs in the growth of any cell. ensures multiccellular organsims have genetic consistancy. all the cells have the same genetic information. some ornagisms can regenerate parts of their body with mitosis such as starfish. also allows old copies to be replaced by new ones. 

Asexual reproduction- organisms can reproduce without producing games. grow a copy of themselves by mitosis producing offspring identicle to them. bacteria undergo binary fission, the outgrowth then detatches. common in plants, vegetative reprosduction. 

some can produce sexually and asexuall- liverworts, mosses. 

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Stem cells

Stem cells are undifferentiated (unspecialised cells)

they keep dividing

can rise to other cell types

Totipotent stem cells (from early embreyos)-- can give rise to all cell types including embryonic stem cells

Pluripotent stem cells (from older embreyos)-- can give rise to most cell type but no embyonic cells

Blastocyst- 5 days after conception, hollow balls of cells. outer layer forms the placena. and the inner 5 cells form the developing embreyo. These are the pluripotent embrryonic stem cells. 

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Cells becoming differentiated

The embryo develops into a multicellular body and the cells become differentiated. loose capacity to develop into a wide range of cells, become specialised. 

Multipotent- some cells retain a certain capacity to give rise to a varitey of diffeent cell types. Neural cells. 

differentiation is irreviersable

plant cells- remain totipotent throughout life. so can be cloned and reproduced, they can dedifferentiate. reproduced in tissue culture.

small pieces of plant- explants. they are sterilised and put on a agar medium with nutrients to grow. the cells divide to form a mass of undifferentiaed cells, CALLUS.

can alter the growth regulators cells of the callus can be made to differentiate to form small groups of cells. these can grow into complete plants, geneticaly identicle. 

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CORE practicle- demonstrating totipotency

Take a few plant cells of one type called an explant

place on agar whcih has certain growth regulators (growth hormones) added

cells divide by mitosis to form a cluster of cells

divide cluster of cells and place in tonatiners with agar

add differernt growth regulators which stimulate plant cells to diffeerntiate into roots, stem and leaves

Put tin foil or cling film to stop airborne contaminants entering

RISK: work rapidly reducing the chance of an airborne ornaginsm entering and the foil/film. use agar with no sugar added so there is no food source present for any airborne organism that do enter. remove at end. becareful is agar is hot

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Sources of stem cells

Embryonic stem cells- easy to extract and grow. but ethical issues, poosible rejection by the patients body, risk of infection when cells recieved, risk of stem cells becoming cancerous in body

Adult stem cells- fewer ethnical issues, rejection risk avioded id cells are taken from the patient. But difficult to extract, more difficult to produce different cell types, risk of infection when cells extracted and recieved 

Fused cells- rejection risk avoided if the nucleaus is taken from the patietn, potential for treateing genetic disorders. But ethnical issues with source of embryonic nuclei, risk of infection when cells are recieved and risk of infection when cells recieved also, risk of stem cells becoming cancerous in body. 

main source of embyonic stem cells from unused embryos after IVF. 

human egg cell with nucleaus removed-> fused cell divides to form an embreyo- stem cells from this contain patients DNA- fused stem cell. 

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Using stem cells

Parkingsons- loss of nerve cells in the brain that are involved in muscle control

multiple sclerosis- electrical insulating layer surroung nerve cells break down

type 1 diabetes- caused when the cells in the pancreas produce less than normal levels of insulin

burn- skin cells damages so cannot be replaced.


when does an embreyo become human with human rights? should there be a maximum age for embreyos used in research, should human embreyos be used at ll. is it acceptable to use human embroos speciallly created for research. is it acceptable to fuse an adult human cell with a humen egg cell to create new stem cells.

People working in the stem cell fiels make the decision because they have an understanding of the issues adn what is not possible. final decisions made by HUMAN FERTILISATION AND EMBTYOLOGY AUTHORITY. about research

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Stem cells

Tissue typing- like blood transfusions (rejection)

Therapeutic cloning- have one dipolid cell removed (hair) the cell or its nucleus would be fused with an ovum from the haploid nucles is removed- result in a diploid cell like a zygote (somatic cell nuclear transfusion)

Role of regulating authorities:

promotes advances in the treatment of infertilitty

increase knowledge about causes of gentital disease

increase knowlege about miscarrage

develop effective methods od contraception

and to detect abnormalities in enbryo before implantation

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Controlling development

hats removed and stalks swapped. plants develop hats ith features of both species, because of the chemicals in the cytoplasm.

if the intermediate hats are emoved and new ones grow they will corrispond the the nukceas and chemical messangers.

Dolly: trasported the nuckeus from the mammary gland cell of one sheeo into another sheeps, unfertilised ovum which had its nucleaus removed.  diploid cell produced formed an embreyo which was implanted into another surrogate sheep, gave birth and it was geneticlly identitcle to the cell donar sheep

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Switching genes on

Correct stimulus is givesn to the unsoecilised cells (chemical)

some genes are switched on and become active other genes are switch off

messenger RNA mRNA is made from the active genes only

the mRNA moves to the ribosomes and they read the mRNA and the appropriae protein is made

the protein can permanetly alter the structure and function of cells

B-galactosidase breaks down carbohydrate lactose when it is present , enxyme converts the disaaccaride lactose to monosaccarides glucose and galactose

when lactose is not present a lactose repressor moelule binds to the operator gene and prevents transcription of this gene. if lactose is present the repressor molecule is prevented from binding to the DNA and the gene is exprtessed. Rna polymerase binds. in eukaryotes need RNA polymerase and regulator proetin, gene is uncoiked on promotor region. or proein repressor moelcules can bind to the repressor and orevent attach. so gene is switch off and no transcribed.

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gene expression going wrong

DOP- growth of bones in wrong place, can freeze major joints. caused by gene mutation, genes expressed that produce all proteins in bone but one of these genes is not switched off in white blood cells.

Specialised cells group in clusrters working together as a TISSUE

cells have secific recognition proetins- Adhesion moleciules on cell surface, they help to recognice other cells and stick to them. part is embedded in membrane but large part is expossed and it binds to complementary proteins. 

cells- specialised for particular function, muscle.

tissue- group of specialised cells working together to carry our one function, muscle tissue

organ- group of tissues working together to carry out one function, mucle and nerve for heart muslce

organ systems- group of organs working toegher to carry out a particular function, circulatory sytem. 

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gene expression

master geners control the development of each segment

master genes produce- mRNA which is translated into signal proteins which switch on genes responsible for producing the proetins needed for specialisation of cells in each segment.

when plants flower cells in the meristem become specialised to form organs that make up the flower. the expression of these genes determine why type of organ will be produced

CEll death: apoptosis- mammals self destruct. suicide genes. switch on their suicide genes. in between fingers. 

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Genes and the envronment

phenotype- genetic make up

Dicontinuous variation- characteristics only contreolled by genes at certain locus. no over lap.

Continuous variation- characteristics affecte by genotype and envrionment. human hieght. bell shaped curve. 

Poligenic inheritance- continuous cariateion, controlled by genes at many loci and the environment. 

monohybrid inheritance- characteristic determined by a single gene

multifactorial- several genes and environment affect it

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genes and the environment


taller men have more children, gradual change in the geneic makeup of the population, greater movements of people, less interbreeding, mor taller people, better nutrition and increased prtein, better growth of children, improved health, reduction of infectios disease, improved sanitation, clean water supplies, better heatin gof houses and better qulatiy clothing reduces eneegy needed to heat body so more enrgy can go into growth.

Hair colour

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making melanin

Dark pigment in skin is called MELANIN

it is made in MELANOCYTES found in the skin and hair folicles


there are RECEPTORS for MSH on the surface of the MELANOCYTES.

The melonocytes put the melanin into organelles called MELANOSOMES

melanosomes are transferred to nearby skin cells and hair cells where they collect around the nucleaus, protecting the DNA from harmful UV damage.

people with more receptors have darker skin and hair and more protection against sunburn.

UV increases MSH and receptors making the melanocytes more active and causing skin to darken. uv light cause chemical and physical cahnges to melanin and proteins in hair cells, hair lightnes due to destruction of the melanin by uv light. 

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seasonal colour change

white winter coat is grown in summer and growns under the brown summer coat and revealed when the summer coat is moulted. 

foxes produce fewer MSH receptors in summer, so MSH has no effect and no melanin is made in the hair folicles

To make melanin animals use the enzyme TYROSINASE-

changes the amino acid tyrosine into melanin

some animals have mutant allels for tyrosinase. they enzyme is inactive at normal body temperature, tips are more darker. 

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monoamine oxidade breaks down the neurotransmitter to regulate bheavour and stress.

some individuals have rare mutation in MAOA gene and produces no enzyme. they exhibit aggressive and sometimes violent behaviour. 

research study- 2 allels for this gene, one results in high levels oft eh enzyme and others are low levels. 

only focused on boys because it occurs in the X chromosom and males only have one allele

childhood maltreatment was associated with antisocial behaviour as adults. no direct link with MAOA. but children with high levels of MAOA were less likely to exhibit aggressive behaviours than those with low levels. 

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occurs when a rate of cell multiplication is faster than the rate of cell death, causes a growth of a tumor. often in tissues with high rate of mitosis such as lung, bowel, gut or bone marrow,.

cancers caused by damage to DNA, by physical factors such as UV ligh or asbesos. or carcinogens or cell metabolism. mutations can occur when cells divide.

cell cycle is controlled by proteins so they can stop the cycle and prevent progree. the proteins activate or inhibit enzymes that initiate the reactions.

ONCOGENES- code for proteins that stimulate the transition from one stage in the cycle to the next. mutations in the gene can lead to cell cycle being continually active, causing excessive cell division-tumour.

TUMOUR SUPRESSOR GENES- produce supressor proteins that stop the cycle. muatations means no break in the cycle. P53- inhibits enzymes at the G1/S phase, preventing cell from copying DNA. mutation- cannot stop going into this stage. skin,colon bladder and breast cancer. cancer more likely in older people because they accumiliated more mutations.

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inherited- close realtives, mutations in the BRCA1 predispose a person to breast  cancer. funcinoning BRCA1 gene produces protein to repair DNA, mutated one may get cancer later in life, the other allele becomes damaged in breast tissue. more suceptable to cancer through environmental damage. 

Environment- chemical/physical. smoking increases cancer, through carcinogens in tar, it lodges the bronchi and cause damage to DNA. Uv damaged DNA in cells, mole affected can grow bigger and develop into a tumorur, i fnot removed it can soread to other parts of the body. 

diet with fresh fruit and veg provides antioxidants which destroy radicales, produced by smoking and UV contributing to agine and cancer through DNA damage.

cancer triggered by virus infection- hepititus, cervical cancer. virus RNA may contain an oncogene which is psed on and transfered into cells.

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these are really good thanks!


Thanks for these, should help me tomorrow:)


You are a legend he put the AS snab revision guide and the text book together pure genius:D


terrible spelling, but a lot of hard work has been put in and the notes are good :)

just spent an hour fixing them up on Word!

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