Biology

• cell membrane- surrounds the cell, controls what substances pass into and out of the cell. e.g.oxygen, carbon dioxide and gluecose.
• nucleus - contains DNA  and controls the activity of the cell.
• respiration occurs in the mitochondria

plant cells.

• a large centeral vacuole is filled with cell sap and keeps the cell ridgid.
• many plants contain chloroplasts.

• bacterial cells have no nucleus.
• have a single loop of DNA within the cytoplasm
• have a cell wall but not made of cytoplasm
• some bacteria have a whip-like tail for movement called flagella.

microscopes and studdying bacteria.

• modern light microsopes can magnify specimine more than 1500 times.
• electron microscope, invented 1930, magnify up to 2 million times. uses beam of electrons to produce a clear image

• nucleus contains all genetic information on chromosomes.
• genes- chromosomes made by DNA divided to form genes.
• each gene code is for a specific protien.
• DNA consists of two coiled trands formint a doule helix.

adenine (A) and thymine (T)               these are called complimantary base pairs and are joined

cytosine (C) and guanine (G)                                   by weak hydrogen bonds.

                                                           the order of basses determines the types of protein made.  

rosalind franklin and maurice wilkins

• used photography to study the shape and size of the DNA molecule.
• from this they were able to work out how the atoms were arranged in the molecule.

james watson anf francis crick

• used daata from many studie to build a 3D model of DNA showing its double-helix structure.

the human genome project (HGP)

• scientists from all over the world have come together will all their data to figure out the 3 bilion base pairs that make up the human genome.
• this has helped us gain knowledge and come up with treatment and cures for genetic dissorders.

• removing genes from the DNA of one organism an inserting it into the DNA  of another.

      (example: the gene for making human insulin can be inserted into the bacterial plasmid DNA. the bacteria will then produce human insulin, which can be usde by people with diabetes.

Risks with genetic modification.

• producing crops that its not intended to such as weeds (farmers).
• food may have harmful effects that we dont yet know of.
• GM crops are also very expensive for farmers to grow

• diploid -when the body cells have two copies of each chromosomes in the nucleus. the divide by a process called mitosis.
• mitosis - where each chromosome makes a copy of itself. (occurs in growth, repair of damaged tissue and asexual reproduction)
• during fertilisation two haploid gametes fuse to forma a diploid zygote. this develops into a new individual. this produces offspring with mixtures of both parents DNA.
• haploid gametes are produced by meiosis, (chromosome pairs are separated). this produces four daughter cells, each with half the normal of chromosomes as a normal body cell.

clones - asexual reproduction produces genetically identical offspring.

• plants can easily be cloned by encouraging bits of leaf, stem or root to develop into whole plants.
• animal cloning. nucleus is removed from a body cell to be cloned, then inserted into an egg cell that has had its haploid nucleus removed. egg cell then stimulated to divide by mitosis and then the resulting embryo is implnted into the uterus of the mother.

• cloning is useful for copying individuals with disirable charecteristics.
• however only a few clones are coppied successfully
• cloned animals are not healthy as normal animals, usially dying young (many people think cloning is wrong)

embryonic stem cells - when the cell of an early embro is oung and has the ability to develope into any type of specialised (differentiated) cell.

• adult humans - only contain few stem cells, such as those found in bone marrow. can only deveop into one or few different cell types.
• in most countries it is illegal to clone humans
• in many countries it is legal to clone human embryos for stem cell research. some people think against it and say that it is destroying what could be a human being. others say that it is helping us find cures for human dissorders.  
• using adult stem cells is more ethical for research than embryonic stem cells
• adut stem cells have been used in leukaemia but it is not always successful as the body tends to reject cells from other people.

• the order of bases on DNA  strand forms the gnetic code.
• the four bases can be arranged in any order
• there are 20 different amino acids in thuman roteins; each is coded for by a specific group of three basses
• during protein synthesis, new protein is built from a chain or amino acids. there controlled by the sequences of bases in the DNA.
• the two stages of protein synthesis - 1st - transcription, takes place in the nucleus, DNA unzips and a molecule of complementary RNA forms against one of the DNA strands.-2nd - translation, when the RNA moves into the cytoplasm and attaches to a ribosome. this moves along the strand, releasing their amino acids which form a growing chain.
• RNA only has one starnd and the base thymine is replaced by uracil.
• the complete chain of amino acids is called a polypeptide. this twists and folds to form a protein.

• every protein has a specific number and sequence of amino acids
• different shaped protein molecules have different properties. e.g. the shape of haemoglobin  enables it to carry oxygen.
• the shapes of enzymes means it works in a specific way.

a mutation is a change in the sequence of bases in the genetic code.

• if the mutation results change the amino acid sequence it will change and effect the way they fold to form protein. this will also effect the way the protien works. thsi could be harmful, e.g. sickle cell mutation which causes the red blood cells to be misshaped and stick together. blocking small blood vessels.
• mutations can be benificial or have no effect at all.
• they are benificial by giving some bacteria to create resistance agains antibiotics.

• a catalyst is a substance that speeds up a chemical reaction without being used up itself.
• some enzymes speed up synthesis reactions inside the cells, where small substrate molecules are joined together to make larger product molecules. 
• other enzymes speed up reactions outside cells, where large substrate molecules are broken into many smaller product molecules. an example of digestion.
• in all reactions enzymes remain the same and can repeat its action time and time again.