Topic 3- voice of the genome

basic unit from which living organisms are built. can be specialised for a particular function

a group of one type of specialised cell which work together to carry out a specific function

a group of different tissues which work together to carry out one or more functions

a group of different organs working together for the same function

• large gamete- many sperm able to fit for increased chances of fertilisation, contains lipid droplets for energy during fertilisation

• zona pellucida- hardens when one sperm has entered to prevent polyspermy

• cortical granules (lysosomes)- release enzymes that cause the zona pellucida to harden

• cytoplasm with protein and lipid droplets- food source to supply energy for cell division of the fertilised ovum

• haploid nucleus- contains half the number of chromosomes so the diploid chromosome number is restored at fertilisation. mixing of alleles allows for genetic variation

• flagellum allows sperm to swim to reach the ovum

• many mitochondria allow it to carry out aerobic respiration and release energy as ATP so the tail can move

• acrosome- specialised lysosome that contains and releases digestive enzymes that hydrolise the zona pellucida to enable to sperm’ entry into the ovum

• haploid nucleus

digestion of the zona pelluucida to allow the sperm to enter the ovum

hardenig of the zona pellucida to prevent polyspermy

when the sperm nucleus fuses with the ovum nucleus fertilisation is complete

46 in total, so 23 pairs

half the number of chromosomes of a somatic cell

full number of chromosomes found in a somatic cell, with two copies of each chromosome

• creates haploid cells, to maintain the diploid number after fertilisation

• ceates genetic variation in gametes and therefore offspring

random aligning of maternal and paternal chromosomes along the equator of the cell to produce new combinations of chromosomes/ alleles

breaking and rejoining of non-sister chromatids on the same chromosome pair causes exchange of alleles, followed by recombination of alleles between chromatids

an undifferentiated (unspecialised) cell that can give rise to other specialised cell types- there is no limit to division. can by totipotent, pluripotent, or multipotent

when an undifferentiated stem cell can give rise to all specialised cell types (216 in the human body). there is no limit to division, and all genes are switched on

when an undifferentiated stem cell can give rise to some specialised cell types except totipotent embryonic stem cells. no limit to division, some genes switched off

An undifferentiated cell which can give rise to only specialised cell types of a closely related family. many genes are switched off.

• can be a zygote (fertilised egg) or 8 cell embryo- totipotent

• can be the inner cell mass of a blastocyst- pluripotent

• disadvantage: ethical issues as they are obtained from spare embryos in IVF and risk of rejections, infection, or cancer when used in treatments

from the umbilical cord blood or placenta- pluripotent

from the bone marrow or brain/connective/skin/liver cells- multipotent

disadvantage: are multipotent, limitations to tissues able to be given ise to, few present in the body, difficult to extract

plant cells remain totipotent throughout life so a complete plant can be grown from a fragment/explant by plant tissue culture

an explant of a plant tissue is placed on a sterile agar containing nutrient and growth regulators- done by aseptic technique. the explants are placed under a light bank for 4 weeks and the cells will differentiate to create a genetically identical clone of the original plant

• improve plant and food crop species

• produce increased quantities of plant chemicals used in drug production

• produce commercial plants that are difficult to grow from seed

• conserve endangered plant species

• give rise to specialised cells in the body to replace dead or damaged tissue

• producing tissues or organs for transplant

• to treat diseases caused by damaged cells

the nucleus of an egg cell is removed. a diploid somatic cell is removed from the patient and the nucleus from the patient’s cell is placed inside the egg cell. the new cell is stimulated electrically to divide by mitosis to form a blastocyst. pluripotent stem cells are removed and encouraged to develop into tissues/organs identical to those of the patient. tissue is not rejected as cells are genetically identical to the patient’s own.

adult/multipotent cells whic have been genetically reprogrammed to become like embryonic stem cells, by being forced to express genes and factors important for maintaining the defining properties of embryonic stem cells

• decide on maximum age of embryo allowed to be used for research

• to consider ethical issues

• to check acceptability of the source of stem cells

• stop human cloning

• stop unnecessary repeating of research

• offers treatment to patient of diseases

• multipotent stem cell research is slower in progression

• could still happen in other countries if banned in the UK

• spare IVF embryos would be destroyed anyways

• research with embryonic stem cells is needed to develop use of adult ones

• embryo is not considered new human unless viable

• embryos are considered unborn children

• much embyonic stem cell treatment may be fraudulent, badly regulated, and exploitative of suffering

• waiting a few years might lead to the same benefits through multipotent stem cells

• diverts funding away from alternatives

• an embryo becomes a new human at moment of conception

nuclear division of the nucleus where two genetically identical daughter diploid nuclei are produced from one parent diploid nucleus. it is a stage in the cell cycle

• to produce 2 new genetically identical cells to the parent cell, each with the diploid number of chromosomes

• to increase cell numbers for growth

• to replace damaged or dead cells to repair damaged tissue

• asexual reproduction

• G1 phase- cell growth, organelle and enzyme production

• S phase- semi-conservative replication of DNA and doubling of cell contents

• G2 phase- cell growth for proteins involved in mitosis

• prophase- condensing of chromosomes, centrioles move to opposite poles and form the spindle. nuclear envelope breaks down

• metaphase- chromosomes attatch to spindle fibres by their centromeres and line up along the equator

• anaphase- centromeres split and chromatids are seperated. spindle fibres pull both sets of chromatids to the opposite poles

• telophase- chromosomes decondense and nuclear envelope reforms around both groups, spindle breaks down

ring of protein filaments on the inside of the cell surface membrane contract and constrict to divide the cell. plant cells synthesise a new cell plate down the middle of the cell

an example of gene expression in the E.coli bacterium. the chemical stimulus for switching on the β-galactosidase gene is lactose

DNA is uncoiled and a regulator protein (transcription factor) and RNA polymerase bind to the promoter region, switchig the gene on. it can now be expressed by transcription and translation

protein repressor molecule binding to the promoter region causes the attatchment site to be blocked. repressor molecule could also bind to regulator protein

correct chemical stimulus is required, some genes are switched on or off. mRNA only transcribes switched on genes so that different proteins are made in different cells.

proteins produced permenantly modify a cell to specialise it

similar specialised cells recognise each other using adhesion/recognition molecules- glycoproteins on the cell membrane, which have complementary shapes and can bind to each other through the tissue fluid surrounding cells to form a tissue

the epigenome helps to control the change from a zygote to an adult. during development epigenetic changes will bring about specialisation of the cell, where signals can result in changes to the epigenome that alters the genes transcribed

control the development of segments of an organism. the master gene produces mRNA that is translated into signal proteins which switch on the genes responsible for producing the proteins needed for specialisation of cells in each segment

programmed cell death- cells die during normal development of an organism

the differences that exist between individuals

a range of phenotypes and genes at different loci and also environment, for example height and weight

phenotypes fall into discrete groups, with genes at one single locus- not affected by environment. eg, blood groups and sex

when more than one gene codes for a single characteristic, with each gene at a different locus. genes interact with each other and have additive effects. it contributes to continuous variation

many genes involved each with a small effect. they interact and the additive effect of the alleles produce many different genotypes and effects of the environment may cause more variation

diabetes, coronary heart disease, alzheimer’s, schizophrenia, and some cancers

the position of a gene/allele on a chromosome

linked genes are found on the same chromose at different loci. they have a high chance of being inherited together, because when chromatids seperate in mieosis II all the genes on the chromatid move as one unit and enter the same gamete. the greater distance between the loci, the greater the likehood of crossing over happening and seperating them

an allele or gene responsible for a trait is located on a sex chromosome, and expression of this trait is related to gender

chromosomes that are not sex chromosomes. humans have 22 pairs of them

• colour blindness

• haemophilia

• eye coour in drosophila

• high UV light causes more MSH to be produced by the brain and more MSH receptors to form on melanocytes

• more MSH binds to the receptors causing gene activation and more melanin made

• melanocytes make more melanosomes, which are transferred to skin cells where they gather around the nucleus to screen it from UV light protecting DNA from sun damage- skin darkens

exposure to UV causes chemical and physical changes to melanin causing hair to lighten

disease resulting from uncontrolled cell division which forms a malignant tumour (mass of abnormal, unspecialised cells) which invades and destroyes surrounding tissue

• environmental mutagens increase the risk eg UV

• mutations occur in DNA of tumour repressor genes or protooncgenes (genes that code for proteins that regulate the cell cycle)

• cell cycle is disrupted as there are no stops on it, leading to uncontrolled cell division

• lack of apoptosis, so rate of cell multiplication by mitosis is greater than the rate of cell death

• abnormal mass of unspecialised cells forms

• cells do not become specialised and growth cannot be controlled

• some cancer cells break off and travel to other parts of the body and cause secondary tumours

• carcinogens in cigarette smoke- cause mutations in DNA in lung cells

• UV radiation- causes mutations in DNA skin cells, tumours can develop from an established mole

• free radicals from smoke UV and cell metabolism may cause mutations, lack of antioxidants to neutralise free radicals increases risk

• viral infection- virus’s DNA may contain an oncogene which affects the cell cycle