T1 BIO S2

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DNA

• deoxyribonucleic acid

• structural unit of info in cells

• stores and transmits genetic info, universala

Chromosomes

DNA in prokaryotes

• found in the nucleoid region

• circular dna, doube stranded

• once chromosome

• nucleoid region also contains RNA and proteins

• plasmids - small amounts of circular DNA seperate from chromosomal

DNA in eukaryotes

• found in nucleus

• human somatic cells have 46 chromosmes (23 pairs) - 22 autosomal and one pair of sex

• set of human chromosomes - karyotype

DNA in eukaryotes cont.

• arranged in condensed linear strands - DNA molecules and histone protein

• ends of chromosome have short DNA lengths called telomeres

• telomere protects tips of chromosome from breakdown, stop them from binding to each other

• chromosmes are only visible w light microscope when condensed (tightly coiled around histone)

chromosomes in eukaryotes - condensed and decondensed

• decondensed - chromatin, important it can be accessed during drowth and syntheesis of cell so DNA, protein and RNA synthesiss can happen

• must condense for cell division to prevent damage and ensure identical copies are transwered

membrane-bound organelles with DNA

• mitochondria (mtDNA) and chloroplasts (cpDNA)

• both double stranded, circular, not bound to histone

• theorised that the reason they have DNA is because they were once free living unicellular organismsn

2 reasons for DNA strcuture

1. make identical copies so genetic info can be passed from cell to cell and inherited by next gen

2. provide code that can be used by cells to manufacture protein molecules

nucleotides include what? and are are bonded togehter by what type of bond?

• bond - covalent bond

• pentose (5-carbon) sugar - deoxyribose

• phosphate group

• one of 4 organic bases - adenine (A), thymine (T), cytosine (C), guanine (G)

DNA directionality, phosphate and sugar ends

• phosphate of one nucleotide attatched to sugar of next - backbone alternates

• one end of DNA has phosphat other sugar - giving directionality

• end of strand with phosphate sticking is called 5’end (5 prime) - beginning of strand

• sugar end with hydroxyl group is 3’ end (3 prime)

• therefore sequence of dna written in 5’ to 3’ direction

• phosphate is negatively charged, DNA has overall negative charge

bases

• each form weak hydrogen bonds with complementary base - easy to break and reform

• important for dna replication - break apart double helix to expose bases for base pairing

• A to T, C to G

reading the strands and strands property

• DNA assembly has 2 complementary strands linked by complementary base pairs

• read in opposite direction, always start at phosphate then to sugar end

chromosome stuff

• made of genes - unique sequence of bases on one strand of DNA (coding strand)

• varies from one DNA molecule to other - enables it to be so versatile and diverse

• diff species have diff characterists, therefore diff no of genes because they need hundreds of proteins to function

• diff in chromosme no, base sequence, length of DNA molecules

DNA replication - general info (NOT THE PROCESS)

• nucleoid region in prokaryotes, nucleus in eukaryotes

• semi-conservative (see flashcard)

• since the DNA strands of the parent are complementary, nucleotides are added in the opposite direction

• 5’ to 3’ direction by DNA polymerase to expose bases of old strands

• product is 2 identical double-stranded DNA molecules

• amount of DNA doubles during replication before chromosomes separate during cell division - no of chromosomes stays the same

semi conservative replication

each double strand consists of one old strand and one newly synthesised one

DNA replication summary

1. helicase enzyme breaks hydrogen bonds between complementary bases joining 2 strands, unwinds and exposes bases, creating a replication fork

2. topoisomerase prevents supercoiling at the fork, and SSB (single stranded binding proteins) proteins prevent seperated strands from coming back together

3. primase attatches to strands and creates a short RNA primer to show DNA polymerase where to start.

4. DNA polymerase adds free DNA nucleotides to exposed corresponding bases on seperate strands according to complementary base pairing rule

5. new DNA synthesised in 5’ to 3’ direction - DNA polymerases add DNA nucleotides to 3’ end of DNA strands

6. DNA polymerase deletes RNA primers and adds DNA nucleotides in their place

7. Ligase joins fragments on lagging strands together

8. DNA polymerase does a double check

9. new double-stranded DNA rewinds to double helix, joined at centromere

gene

• unique sequence of DNA nucleotides that code for polypeptide chain, protein, or RNA molecule

• heritable, control specific characteristics

• located at specific locations (locus)

• 3 parts: promotor region, coding sequence, terminator sequence

genome

• total no. of genes in an organism

• genomics - study of genomes

• 1990 - internation effort to map entire human genome (location of all genes in all chromosomes) - first draft published 2001 and used in various fields

RNA

• ribonucleic acid, essential for expression and regulation of genes

• made of nucleotides

contains:

1. pentose (5carbon) sugar called ribose

2. phosphate group

3. adenine+URACIL (2 hydrogen bonds), cytosine+guanine (3 hydrogen bonds)

• 4 major types - messenger RNA (mRNA), transfer RNA (tRNA), ribosomal RNA (rRNA), micro RNA (miRNA)

• all are single stranded

exons

• coding sequences of DNA thats translated into polypeptides/proteins

• 2% of DNA is exons

• highly conserved because changes to code can result in change to translated protein

introns

• noncoding sections of DNA, do not code for polypeptides/proteins

• can be transcribed into RNA molecules such as tRNA, rRNa, and miRNA

• 98% of human DNA is introns

• less conserved as they are non-coding

• most prokaryotes dont have introns but have exons bceause they need coding sections to code proteins

genes for exons and introns

• contain both

• trasncirbed into premature messenger RNA (pre-mRNA) strands in nucleus as part of protein synthesis

• introns must be spliced out of pre-mRNA forming mature mRNA before transltated into amino acid sequence → process is called RNA splicing

messenger RNA (mRNA)

• syntehsised using DNA as template in process known as transcription occurs in nucleus,

• following some post-transcriptional modification to become mRNA it moves to cytosol

• single stranded, consists of sequence of RNA nucleotides - varied length

• codes for specifc sequence of amino acids

• every 3 bases (RNA codon) codes for specific amino acid

transfer RNA (tRNA)

• roughly 80 nucleotides long, 3 dimensional clover leaf shape

• contains anticodon - 3 bases complementary to specific mRNA codon

• carry specific amino acid at opposite end of anticodon

• function - place specific amino acid into correct sequence in polypeptide

• after it transfers, it collects another corresponding amino acid in cytosol

• amino acid tRNA attatchment involves enzymes with specific shapes so each amino acid is only ever attathced to their corresponding tRNA

ribosomal RNA (rRNA) and ribosome facts

• essentially mRNA but when its at the ribosome

• ribosomes are made of them and protein molecules

• ribosomes - sites of translation in protein synthesis, found often attached to ER in cytoplasm

• move along mRNA tranaslating mRNA into amino acid sequence (polypeptide molecule)

microRNA (miRNA)

• non-coding RNA (ncRNA) molecules, approx. 22 nucleotides

• regulate gene expression after transcription

• exert regulatory action by binding to a small section of a specific mRNA molecule - prevents it from being translated

• small section of mRNA becomes double stranded - prevents ribosome from accessing full mRNA code and expression of that gene

amino acids (aa) +bond in polpeptide chain

• 20 different ones

• building blocks of polypeptides and protein molecules

• polypeptides have a specific sequence of amino acids linked together by aSTRONG PEPTIDE BONDS

• proteins can be one chain folded into a precise 3D shape or more than one chain linked together

coding strand

• aka non-template strand, sense strand

• codes for gene of interest

• determines correct mRNA sequence but doesnt take direct part in transcription

• mRNA produced from transcription will have same code as coding strand (except T is replaced with U)

• consists of triplets of DNA codons

template strand

• aka anti-sense strand

• complementary to coding strand

• provides template genetic code for growing mRNA strand to form against

• mRNA produced is complementary to template strand, except T is replaced with U

• contains DNA anticodons

anticodons and codons in mRNA and tRNA and template and nontemplate strands

• coding strand has DNA codons

• template strand has DNA anticodins

• mRNA molecules are synthesised against template strand in complementary pattern, therefore have mRNA codons (correspond to DNA codons in coding strand)

• tRNA molecules with complementary anticodons to mRNA codons bring amino acids to polypeptide chain

genetic code

• codons are smallest unit necessary to code for all 20 amino acids

• make up both coding DNA strand and mRNA strands

• mRNA molecules transmit copy of gene from coding strand from nucleus to ribosome - sequence of codons is translated into amino acids

• codons are base triplets thereofre, no of nucleotides making mRNA must be x3 no. of amino acids in protein

Transcription

• occurs in nucleus of eukaryote

• mRNA molecule is syntehsised from gene on DNA
  
  1. initiation - RNA polymerase, once in contact with an activator protein, binds to the promoter region of DNA strand and begins to unwind it
  2. elongation - RNA polymerase moved 5’ to 3’ direction (3’ to 5’ on the template strand), makes RNA transcript by adding nucleotides to growing RNA strand
  3. termination - once RNA polymerase reaches termination site, transcript (mRNA) seperates from template, 2 DNA strands reform double helix

RNA splicing (part of transcription)

• intial product of transcription is primary transcript - has both introns and exons

• only exons are expressed as polypeptide, therefore introns in the pre-mRNA molecule (after transcription) must be removed

• occurs in the nucleus, produces mature mRNA molecule

• intron/exon junction recognised by snRNP proteins, cluster together to form splieceosome

• splieceosome cleaves introns, joins 2 ends of exon togehter - mRNA now ready to leave for cytosol (mature mRNA)

translation general info

• polpeptide chain is built using sequence of codons in mature mRNa molecule

• 3 stages - initiation (use of start codon AUG), chain elongation (building amino acid sequence from codons), termination (completion of mRNA sequence with stop codon

• happens at ribosome which consists of two tRNA binding sites

advantages of many ribosomes

• can move along mRNA one after the other - leads to syntehsis fo many copes of polypeptide in short time period

• large number of proteins are needed for multicellular organisms

translation process

• ribosomes read mature mRNA strand in 5’ to 3’ direction

• two tRNA molecules move to ribosome sites, bond with mRNA (detmerined by complementary codon/anticodon)

• ribsome faicllitates formation of peptide bond between 2 amino acids

• ribsomes moves along mRNA - growing polypeptide chain

• tRNA molecules keep bringing amino acids until stop codon is reached

• mature mRNA continues to be translated, many copies of polypeptide chain are formed until miRNA message is sent

• miRNA binds to mature mRNA (complementary fasion) - deactivates expression of this gene

promotor region, coding sequence, and terminator sequence

the 3 parts of a gene

• promotor region - non-coding sequence, initiates transcription, typically located immediately upstream coding sequence. binding of RNA polymerase to it is controlled by transcription factors (in eukaryotes)

• coding sequence - region of DNA that is transcribed

• terminator sequence - part that tells RNA polymerase to stop transcribing

functions of proteins

• catalysing reactions (e.g. enzymes)

• cellular communication (e.g. hormones)

• inactivating or neutralising invading molecules, substances, or organisms (antigens) (e.g. antibodies)

• providing structure

• transport of substances (e.g. oxygen via haemoglobin)

• contraction and movement (e.g. muscles)

• regulation of genes (e.g. activator protein, repressor protein)

proteins (and functional protein def)

• made of amino acids which make polypeptide chains - can be many chains (many genes to code for them)

• each protein is unique as made of varying combos of aa and can vary in type number or sequence

• unique shape determines specific function

• consist of one or more polypeptide chain, folded to produce specific shape

• functional proteins - recognise and bind to other molecules that are complementary in structure (4 different types - primary, secondary, tertiary, quaternary)

primary structure

• unique, linear sequence of amino acids in polpeptide chain held togehter by covalent peptide bonds - result of interactions between amino acids in primary structure

• aka polypeptide

secondary structure

• localised coiling or folding of polypeptide chain, caused by hydrogen bonding between amino acids

• intermediated between primary and folding into 3D shape of tertiary

• 2 most common shapes - alpha helix (coiling) and beta pleated sheet (folding)

• many antibodies have strucutre made of mostly beta pleated sheets, myoglobin is protein with mostly alpha helixes

tertiary strucutre

• 3D shape of a polypeptide caused by the way the polypeptide chain is folded

• forms spontaneously because of forces of attraction between aa in the polypeptide chain

• many types inc. hydrogen bonds, ionic bonds, strong covalent disulphide bonds

• folded shape - globular proteins

• 3D shape with unique folds, grooves, and clefts determine function of protein, therefore 3D structure is critical to function

quaternary structure

• protein consisting of 2 or more polypeptide chain, quaternary strucutre forms from polypeptide chains chemically bonding together

• e.g. haemoglobin - 2 alpha and 2 beta chains bonded together

enzymes

• most are globular proteins, increase the rate of a specific chemical reaction or catalyse it

• have an active site - formed by folding and binding of protein chain - that substrate (s) or reactant (s) bind to

• bc of the shape of the active site, enzymes have specificity - each enzyme only has one substrate

receptor proteins and peptide/protein hormones

• proteins are found on inner and outer surface of cell membranes, play major role in membrane structure and function

• receptor proteins have specific shape that bind toone specific messenger molecule with complementary shape (e.g. complementary hormone)

• hormone - chemical messenger molecules

• not all are proteins, some are lipid based

• differences in primary, secondary, tertiary, and quaternary structures allow them to bind to specific cell membrane receptors

• e.g. thyroxine - metabolic activity, insulin

hormone signalling includes processes of:

• synthesis of hormone

• storage of hormone in gland, and secretion into bloodstream

• transport via blood to target cells

• binding to complementary receptor protein in cell membrane of target cell

• relaying message to cell nucleus, leads cellular response

antibodies

• antigens are foreign molecules (non-self) usually found embedded in surface of viruses or cells

• lymphocytes produce protein molecule antibodies as part of specific defence mechanism

• act by binding to specific antigen in complementary manner, deactivates or neutralises

• particular 3D shape of quarternary structure allows antibody to bind with and inactivate antigen

regulatory proteins

• important area of contemporary research

• cells have many ways toregulate/control swithcing genes on and off

• genes are switched on when transcription can happen and opposite for off

• repressor proteins bind to DNA section near gene (promoter region), preventing RNA polymerase from bindign and stopping transcription

• activator proteins to DNA near gene assists RNA polymerase binding and promotes transcription

proteomics (and bit abt proteome, cells and diff proteins)

• proteome - all proteins in cell or organism at specifc time

• cell needs diff proteins at diff times of day and through life, no of proetins differ from cell to cell

• each cell uses or expresses specific section of genome to make proteins it needs

• proteomics - study of proteins (abundance, variations, modificatinos)

• biomarkers - molecules (e.g. proteins found in blood) indicating abnormal processes of diseases

• proteins are molecules of structure and funcion in cell

peptide/protein hormones

• hormone - chemical messenger molecules

• not all are proteins, some are lipid based

• differences in primary, secondary, tertiary, and quaternary structures allow them to bind to specific cell membrane receptors

• e.g. thyroxine - metabolic activity, insulin

enzyme

• globular protein speeds up/catalyses specific chemical reaction within cells

• reactants/substrates are chemically converted into new substances (products)

• breaks chemical bonds in substrate and forms new bonds in product

• are not used up in reactions

active site and enzyme specificity

• region substrate binds to - groove or cleft on enzyme surface

• binding is called enzyme-substrate binding; occurs due to active sites shape

• shape is specific to one substrate

• substate and active site shapes are complementary

• enables specificity, ensuring that only the correct substrate can bind

how do enzymes work

• substrate molecules are bough into an orientation that facilitates breaking/forming of chemical bonds

• bonds in substrate are stressed, lowering the amount of energy needed to break them and therefore the amount of energy needed for the reaction to proceed

metabolism

• metabolism - all biochemical reactions carried out by living organisms

• rate of these reactions - metabolic rate

• Separate biochemical reactions making up a cell’s metabolism are metabolic reaction

• most reactions form part of metabolic pathways

• each step is catalysed by a specific enzyme

induced fit model

• substrate binds to the enzyme by weak bonds, often causes a change of shape of both enzyme and the substrate

• original model - lock and key - enzyme active site, which is like a keyhole to substrate (hence specificity)

• induced-fit model - enzyme and substrate modify each other’s shape in the process of binding

• active site continues to change until substrate is completely bound to it. this is when the final shape and charge are determined

enzymes lowering activation energy

• activation energy - energy required for the bonds of reactant molecules to break

• the lower the activation energy the faster the reaction - less energy is needed to break bonds to initiate the reaction

factors influencing enzyme activity - temperature

• at lower temperatures, activity is low - fewer substrate colliding with enzymes ac’s active site, don’t have enough energy to overcome the activation energy barrier

• as temperature increases, so does enzyme activity - substrate and enzyme molecules will move faster, resulting in more collisions at the active site and hence a greater rate of reaction

• enzyme activity is maxed out at optimum temp

• temp inc above optimum temperature causes the active site structure to be altered (denaturation). substrate can’t bind to the denatured active site, thus activity is 0

factors influencing enzyme activity - pH

• optimum pH - activity is at maximum

• pH change above or below optimum temp denatures the enzyme - substrates can’t bind to the denatured active site, enzyme activity decreases to 0 quickly

• enzyme-substrate binding is reduced when a change in pH alters the shape of the enzyme or substrate - no longer complementary

• optimum pH is different for enzymes

• Chemical buffers in the body help stabilise pH and allow enzymes to catalyse reactions

factors influencing enzyme activity - concentration of reactants

• low substrate concentration - fewer substrates to collide with the enzyme active site, enzyme activity is low

• as concentration of substrate increases, enzyme activity increases - more frequent collisions between enzyme and substrate at active site

• higher substrate concentrations - most active sites on the enzyme are occupied by substrate, increases in substrate concentration begin to cause smaller and smaller increases in enzyme activity

• increase in substrate concentration above optimum substrate concentration don’t lead to greater enzyme activity - all active sites are occupied by substrate (saturated)

factors influencing enzyme activity - concentration of enzyme

• same logic as substrate

• difference is that substrate is the limiting factor

factors influencing enzyme activity - concentration of products

• The activity of some enzymes is regulated by substances that bind to the enzyme NOT AT THE ACTIVE SITE but in the ALLOSTERIC SITE

• causes a reversible change to the active site and alter binding

• end products of metabolic pathways can act as inhibitors of pathway action associated with the control of metabolic pathways in cells

• known as end product inhibition - occurs when the presence of a high concentration of the end-product of a metabolic pathway inhibits the production of products that stop the production of the end-product

factors influencing enzyme activity - inhibitors (competitve and noncompetitive)

• molecules that reduce rate of enzyme-catalysed reactions that can lead to the accumulation of substrates

• COMPETITIVE INHIBITORS: mimic the structure of the substrate - compete with the substrate by binding to the active site of the enzyme. enzyme-substrate binding is reduced and enzyme activity is decreased

• NON-COMPETITIVE INHIBITORS - do not compete with substrate, bind elsewhere on enzyme at allosteric site. structure/shape of active site changes, preventing binding of enzyme and substrate at active site and reducing enzyme activity

phenotypic expression of genes

• gene pairs of homologous chromosomes control phenotypic characteristics (physical factors expressed from genes)

• alleles - genes of corresponding pairs, alternative forms of same gene

• different alleles exist because genes are subject to mutations

• 2 organisms can look similar but have different genotypes

• 2 organisms can have same genotype but appear different because they’ve been exposed to different environmental conditions

epigentics

• study of how the environment influences gene expression

• epigenome - chemical tags, an additional level of coding on top of the DNA base sequence. do not affect the base sequence, but change how cells read and express DNA

• 2 main types - methylation and acetylation

• epigenetic tags can be inherited and altered by environmental factors

• affected by positive and negative experiences, can be temp or permanent.

• different experiences of individuals as they develop alter the location of epigenetic tags

promoter sequence

• region on DNA that is not transcribed but plays a role in controlling transcription

• RNA polymerase binds to initiate transcription

• transcription factors can also bind to specific base sequences in promoter regions and assist in the binding of RNA polymerase

activators

• bind to DNA and activate/increase rate of transcription

• can bind to other base sequences upstream of the gene and promoter sequence

• activator proteins binding to base sequence can stimulate gene expression

• e.g. of binding it can initiate - triggering RNA polymerase to release from promoter region and start moving along gene

repressors

• binding to DNA and slow/stop rate of transcription

• can bind to other base sequences upstream of the gene and promoter sequence

• repressor binding to other region silences transcription by inhibiting RNA polymerase from binding to promoter region

methylation

• process where a methyl group is added to the DNA strand

• usually occurs at a cytosine base

• does not alter DNA sequence but can influence gene expression

• inhibits RNA polymerase from binding to promoter regions, stopping transcription

• after methylation, genes usually retain methyl groups when cell division occurs and the pattern of methylation is passed onto daughter cells

histone modification/acetylation

• DNA is packed with histone proteins to form chromatin

• acetylation of histone proteins changes RNA polymerase accessibility to genes

• acetylation: chromatin to decondense - loose packing of histone proteins - RNA polymerase can bind to DNA and express genes

• deacetylation: chromatin condenses, histone proteins are more tightly packed, RNA polymerase can’t bind, and transcription won’t happen

• histone proteins can also be methylated - consequences depend on the amino acids within the histone protein being methylated and the number of methyl groups added to that amino acid

translation factors

• translation is controlled as valuable resources like energy and amino acids are wasted, and increases in certain proteins can be detrimental for cells

• translation factors help coordinate the synthesis of polypeptides and proteins

• generally act on mRNA or miRNA

• can increase or decrease translation on mature mRNA

• miRNA, siRNA, lncRNA are focus in s2

• all factors focused in s2 bio are synthesised from non-coding DNA and are caleld ncRNA (non-coding RNA)

small interfering RNA (siRNA)

• aka silencing RNA

• class of translation factors, act on mRNA, preventing translation

• similar in size to miRNA, generally consist of 21 nucleotides

• binds to a specific mRNA molecule in a complementary fashion, promoting the destruction of the mRNA strand

• A specific mRNA strand cannot be translated by ribosomes, and gene expression is stopped

long non-coding RNA (lncRNA)

• have many functions that control gene expression

• longer than miRNA and siRNA, approx. 200 nucleotides

• bind to specific miRNA molecule in a complementary fashion

• as lncRNA binds to miRNA and not mRNA, miRNA cant bind to mRNA and prevent translation

• lncRNA promotes gene expression by inhibiting specific miRNA

factors influencing gene expression ADDD

• gender - some genes are expressed differently in males and females

• chemicals

• temperature

• diet and lifestyle

• trauma

CANCER - pro-oncogenes,

• normally code for proteins involved in cell division

• decreased methylation to DNA can therefore promote cell division and if uncontrolled leads to cancer

CANCER - tumour supression genes

• under normal circumstances, they code for proteins that suppress or inhibit cell division - keeps no. of new cells in a tissue in check and suppress tumour formation

• increased DNA methylation of tumour suppression gene switches them off and proteins suppressing tumour formation can no longer be produced/produced in smaller amounts

• uncontrolled cell division and tumour could develop due to lack of normal cell divison suppression

CANCER - DNA repair genes

• can be activated to produce proteins involved in the repair of damaged DNA

• increased methylation to DNA repair genes results in them being turned off. less damaged DNA is repaired and it accumulates - increases risk of uncontrolled cell division and cancer

cell differentiation

• all organisms that reproduce sexually start as a fertilised egg or zygote, a single cell divides and grows to form blastocyst, then gastrula, then different cells type develop

• every somatic cell contains all genetic info needed to carry out every function but only small portion of this is activated in each cell

• differentiation - process where cells with identical chromosomes and genes become different and specialised in both structure and function

specialised cells

• have specific epigenetic tags, help activate and silence specific genes

• once specialised, cannot differentiate into another type of specialised cell

• epigenetic tags can be passed from parent cells to daughter cells through mitosis - inheritance of these tags ensures daughter cells also become the same type of specialised cell and will be the correct type of cell for that specific organ/tissue

stem cells

• unspecialised and can differentiate into specialised ones

• 2 types - pluripotent and multipotent

• pluripotent - stem cells that have the potential to develop into any human cell

• multipotent- stem cells that can develop into some cell types only

• cell differentiation results in regulation of gene expression; some cells have particular genes switched on and off

• housekeeping genes - certain genes that are always turned on

reasons why cells in different regions or positions develop differently

• signal molecules released from one cell bind to surface cell receptors on target cells nearby and the signal molecules act to regualte genes in nucleus

• interaction of membrane proteins on cells initiates signal molecules. signal molecules include transcription factors

• cell signalling mechanisms in differentiation

cloning

• clone - group of cells or tissue derived from single cell or group of genetically identical organisms

• two clones are genetically identical but are epigenetically different as they are exposed to different environmental conditions throughout life

therapeutic cloning

• use of cloned stem cells in medicine

• stem cells are unspecialised, so scientists can use different techniques to control gene expression and control the type of cell they differentiate into

• research has great potential and is possible to produce a wide range of tissue and enable diseased cells to be replaced with healthy ones

• highly regulated due to ethical considerations - creating new life just to extract stem cells, ending potential life

• possible methods of acquiring stem cells for research:

  • extraction from leftover fertilised ovum from an IVF program (embryonic stem cells)

  • removal of tissue like bone marrow and umbilical cord (adult stem cells)

  • reprogramming ordinary somatic cells in a way that induces them to become stem cells (IPS cells)

• once obtained, used to produce specific tissues in lab, transplanted to patients to replace or repair damaged ones in body or injected directly in specific region of body

• limits - producing tissue that is structurally correct, rejection, development of wrong type of tissue, tumour formation

ction