Brief History of Life on Earth

• Scientists believe that the Earth formed 4.5 billion years ago. • 3.5 billion years ago the first form of life evolved in the form of prokaryotic bacteria. • 1.5 billion years ago the first nucleated cells (i.e. cells with a nucleus – known as eukaryotic cells) appeared. • 0.5 billion years ago multicellular eukaryotes came to existence. Life on Earth images/bee.jpg Life on Earth exists on the surface of our planet known as the biosphere. Planet Earth is the only place in our solar system that can sustain life - as we know it. cell the basic building block of living things; the basic structural and functional unit of all organisms. nucleus the central part of a cell that directs the cell's activities and stores information to pass on to new cells. cell - did you know? The word cell comes from the Latin word cella, meaning a small room. The name was chosen by Robert Hooke when he compared the cork cells he saw to the small rooms that monks lived in. This is an additional info pop-up image images/molecule.png The picture of molecule shows a ...

Cells – The Building Blocks of Life – 1 of 2

• All living things - from bacteria to plants to humans - are made up of cells, the basic unit of life. • Some organisms are unicellular, i.e. consisting of a single cell, such as bacteria. • Other organisms are multicellular, such as humans who have an estimated 100 trillion cells. • Although there are many types of cells, most cells share some common characteristics that include use of energy, movement, growth, division. The light microscope images/microscope1 (Small).jpg Most cells are too small to be seen with the naked eye and require the use of high-power optical and electron microscopes. However, there are cells that are large enough to be visible and the best example is the reproductive cells of chickens - eggs! unicellular consisting of one cell. multicellular composed of more than one cell. largest cell - did you know? The largest known cell is an ostrich egg. This is an additional info pop-up image images/molecule.png The picture of molecule shows a ...

Cells – The Building Blocks of Life – 2 of 2

• All living cells have - an outer covering (cell membrane) that encloses their contents and serves as a semi-porous barrier to the outside environment, - a gelatinous inside (cytoplasm), - and genetic material that stores important information. • There are two general classes of cells: prokaryotes and eukaryotes. What does a cell look like? images/Friedegg (Small).jpg Think of a cell as a fried egg. The yolk is the nucleus, the egg white is the cytoplasm and the cuticula acting as the cell membrane. image2 cell membrane the outer boundary of the cell. cytoplasm the contents of a cell, excluding the nucleus. Description comes here Description comes here This is an additional info pop-up image images/molecule.png

Prokaryotes

Prokaryotes (from greek words meaning before nucleus) are: • Organisms without a cell nucleus (= karyon), or any membrane-bound organelles (such as mitochondria). • The evolution of prokaryotic cells preceded that of eukaryotic cells by 2 billion years. • Prokaryotes are mostly unicellular (in rare cases, multicellular). Example of a prokaryotic organism: Streptococcus pyogenes, the bacterium that causes strep throat (pharyngitis). Without a nucleus images/messyegg (Small).jpg In prokaryotes, the DNA is not membrane-bound (i.e. not confined within the nucleus). In this case the DNA can be found freely on the cytoplasm. Note: that prokaryotic cells are usually rod shaped. The reference to the egg here is used to highlight the difference between prokaryotes and eukaryotes and does not reflect actual sizes or shapes. Prokaryotic cells are much smaller than eukaryotic ones. image2 prokaryotic cell a cell having no nuclear membrane and hence no separate nucleus. organelles Membrane-bound specialised regions within a cell that perform specific functions. Examples include mitochondria (energy-producing organelles), vacuoles (membrane bound sacs, often used for storage), chloroplasts (photosynthetic organelles) etc. Description comes here Description comes here This is an additional info pop-up image images/molecule.png The picture of molecule shows a ...

Eukaryotes

Eukaryotes (from the greek words meaning true nucleus) are: • organisms that have cell nuclei and membrane bound organelles. • may be variously unicellular or multicellular. Example of a unicellular eukaryote: Saccharomyces cerevesiae, commonly referred to as yeast, the organism that makes bread rise and beer ferment. Example of a multicellular eukaryote: Humans. Cultured cells images/helacells (Small).jpg Fluorescent microscopy of human cultured cells. The nucleus (excluding the nucleoli) is stained fluorescent green. The internal environment of the cell is protected by the plasma membrane. The DNA can be found within the nucleus, one of the biggest structures within the cell. The cytoplasm contains other structures such as the mitochondria, ribosomes etc., which are important for the many functions of the cell. Those structures are smaller and therefore not visible unless electron microscopy is used. eukaryotic cell a cell containing a nucleus. nucleus (further defined) one major organelle within eukaryotic cells that contains an organism's genetic information for cell growth and reproduction. Description comes here organelles - did you know? Organelles allow eukaryotes to have higher levels of intracellular division of labour than is possible in prokaryotes. This is an additional info pop-up image images/molecule.png The picture of molecule shows a ...

Prokaryotes Versus Eukaryotes

The major similarities between the two types of cells are that: • they both have DNA as their genetic material • they are both membrane bound • they both have ribosomes The major differences between the two types of cells are that: • eukaryotes have a nucleus • eukaryotes have membrane-bound organelles • eukaryotic cells are on average ten times the size of prokaryotes. Prokaryotes vs Eukaryotes images/celltypes.png Cartoon representations of a eukaryotic (left-hand side) and a prokaryotic cell (right-hand side). Note that eukaryotes have a well defined nucleus that holds the genetic information. Both types of cells have ribosomes. In addition to the plasma membrane, the internal environment of prokaryotes is protected by a cell wall. The flagellum is there to help the cell move. (Image source: Wikipedia) image2 dna Deoxyribonucleic acid (DNA) is a double-stranded, helical nucleic acid that carries the genetic information found in most organisms. ribosomes Minute round particles composed of RNA and protein that can be found in the cytoplasm of living cells and serve as the sites of protein synthesis. Description comes here Description comes here This is an additional info pop-up image images/molecule.png The picture of molecule shows a ...

Human Cells

• Cells have different functions depending on where they can be found in the human body. • For example, there are blood cells, skin cells and bone cells. Each cell looks different and performs a different function. • Cells group together in the body to form tissues - a collection of similar cells that group together to perform a specialised function. • The various kinds of tissues group together to form organs. Red blood cells images/Redbloodcells.jpg This is a micrograph (i.e. image taken through a microscope) of red blood cells. Mammalian red blood cells are circular, biconcave discs packed with haemoglobin, an oxygen-carrying iron protein that gives cells their red color. Red blood cells have no nuclei in the interest of maximising haemoglobin content. (Image source: Wikipedia) image2 tissue A group of specialised (or similar) cells that together perform a particular function, eg. muscle tissue, nerve tissue, bone. organ An organised group of tissues specialised to perform specific functions, i.e. liver. Description comes here Description comes here This is an additional info pop-up image images/molecule.png The picture of red blood cells

Nucleic Acids

• Nucleic acids are the cell's information molecules. • There are two kinds of nucleic acids: Deoxyribo Nucleic Acid (DNA) and Ribo Nucleic Acid (RNA). • DNA - often referred to as the molecule of life - carries the cell's inherited library of information. • DNA holds the instructions for building all the proteins that carry out cell processes. Studying nucleic acids images/cuvette red (Small).jpg Nucleic acids are not visible to the naked eye. DNA absorbs light in the UV range and therefore the amount of DNA in a sample can be determined by measuring the absorbance of UV light. Scientists use spectrophotometers (that is an instrument for measuring the amount of light absorbed by a sample) to estimate the concentration (i.e. how much) and purity (i.e. how clean) of a DNA solution. image2 rna RNA acts as an intermediary in the protein-making process. RNA functions primarily to decode the instructions for protein synthesis that are stored on the DNA molecule; RNA has a single-stranded linear structure and a slightly different chemical composition from DNA. protein One of the four main classes of macromolecules (protein, nucleic acid, carbohydrate, lipid) found in biological systems. Proteins are composed of amino acids joined by peptide bonds. Proteins perform a wide variety of functions in the cell; these include serving as enzymes, structural components, or signalling molecules. This is an additional info pop-up image images/molecule.png The picture of molecule shows a ...

Structure of DNA – 1 of 3

• A DNA molecule is made up of nucleotides. • Nucleotides consist of a phosphate, a sugar (called deoxyribose), and a base. (Look at the image on the right-hand side of this screen for the structure of the phosphate and the sugar) • The bases on the DNA molecule can be Adenine (A), Thymine (T), Guanine (G), or Cytosine (C) or A, T, G, C for short. (Look at the images on the right-hand side of this screen for a graphical representation of these) Phosphate and Sugar images/phosphateandsugar.jpg The phosphate group and the sugar (5-carbon sugar called deoxyribose) are the repeating units on the DNA molecule. For simplicity, the cartoon representations on the right-hand side are being used for illustration purposes in place of the chemical formula. DNA bases images/allbases.jpg Attaching a base to the phosphate-sugar repeating subunits makes a nucleotide. There are only four different bases (A, T, G, C) in a DNA molecule, but each molecule contains millions of these bases in different combinations. Similarly for simplicity, the cartoon representations on the right-hand side are being used for illustration purposes. deoxyribose The sugar found in DNA. It is a monosaccharide, ribose, in which the hydroxyl group (OH) is replaced with hydrogen (H). base A nitrogen-containing (nitrogenous) ring molecule that, in combination with a pentose sugar and a phosphate group, forms a nucleotide, the fundamental unit of nucleic acids (for example DNA, RNA). This is an additional info pop-up image images/molecule.png The picture of molecule shows a ...

Structure of DNA – 2 of 3

• The base (A, or T, or G or C) is attached to the sugar, which is attached to the phosphate to form a nucleotide (see image on right-hand side). • The phosphate of one nucleotide binds to the sugar of the next nucleotide forming the backbone of the DNA molecule. • The bases protrude from the phosphate-sugar backbone and pair with their complementary pairs on another strand (called the complementary strand). The bonds that hold the base pairs together are hydrogen bonds (see image on right-hand side). A nucleotide images/nucleotideB.jpg From left to right, a nucleotide consists of a phosphate group, attached to the sugar deoxyribose that is then linked to a base. Nucleotides, the structural subunits of the DNA molecule, bind together to form the “beads” on the “DNA necklace”. Base pairing images/basepair.jpg Specific bases are chemically attracted and bind to form a base pair (bp). Hydrogen bonds hold the pair together. nucleotide The building blocks of DNA which consist of a base (A or T or G or C), a sugar, and a phosphate group. hydrogen bond A weak, extremely polar type of chemical bond responsible for the properties of water and essential to the integrity of large biological polymers, such as nucleic acids and proteins. This is an additional info pop-up image images/molecule.png The picture of molecule shows a ...

Structure of DNA – 3 of 3

• Nucleotides pair in a specific way. This is known as the base-pair rule (see image top right-hand side): Adenine pairs to Thymine and Guanine pairs to Cytosine • The phosphate and the sugar form the “backbone” of the molecule. The bases protrude and pair to their counterpart on the complementary strand. • The strands then twist to form the famous double helix structure (see bottom right-hand side image) DNA molecule unwound images/doublehelixUn.jpg The order of bases (A, T, G, C) on the DNA molecule varies. The order in which these bases appear in the DNA is the coding for the information carried in the molecule. In other words, the bases serve as a sort of genetic alphabet. DNA double helix images/double_helix (Small).jpg A DNA molecule consists of two complementary strands of nucleotides twisted together to form a double helix. There are ten base pairs per complete DNA turn. The total length of DNA present in one adult human is the equivalent of nearly 70 trips from the earth to the sun and back. (Image source: Wikipedia) complementary With respect to nucleic acids, complementary means that one strand of nucleic acid (DNA or RNA) can pair with and serve as a template for its complementary strand; complementary DNA strands are related by the base-pairing rules: A pairs with T and C pairs with G. dna - did you know? The structure of DNA was discovered in 1953 by James Watson, Francis Crick, and Maurice Wilkins, who jointly received The Nobel Prize in Physiology or Medicine in 1962 "for their discoveries concerning the molecular structure of nucleic acids and its significance for information transfer in living material". This is an additional info pop-up image images/molecule.png The picture of molecule shows a ...

How the code works – 1 of 2

• DNA is the blueprint of life - it has the instructions for making an organism. • The 4 bases (A, T, G, C) have endless combinations just like the letters of the alphabet can combine to make different words, which then make different sentences. • A stretch of DNA can be written in the order that the bases are present on the DNA strand (see image on right-hand side). • This stretch of DNA, also referred to as a sequence, could code for a gene, which in turn codes for a trait (such as eye colour). Coding sequence of the actin gene images/actin (Small).jpg The letters correspond to the order of bases on the DNA molecule that code for the actin gene. Actin is an abundant structural protein present in all eukaryotic cells. If the letters in this sequence were in any other order than the one shown, then the sequence would code for a different gene. Image courtesy of Centre for Bioscience, the Higher Education Academy, ImageBank http://www.bioscience.heacademy.ac.uk/imagebank/ (C) Dr Ijsbrand Kramer image2 gene The basic biological unit of heredity; A gene is a segment of DNA that specifies the structure of a protein or an RNA molecule. dna sequencing The determination of the exact nucleotide sequence in a defined region of DNA. This is an additional info pop-up image images/molecule.png The picture of molecule shows a ...

How the code works – 2 of 2

• DNA holds the information that is necessary to make proteins (click on the image on the right-hand side of this screen for detailed pathway). • The information from the DNA molecule kept in the nucleus is copied onto another molecule called messenger RNA (mRNA) (this process is known as transcription). • Once in the cytoplasm the mRNA binds to ribosomes and then translates the message to produce a protein (this process is known as translation). Protein Synthesis images/trans (Small).jpg From DNA to mRNA to protein: An mRNA molecule, which has previously been transcribed from DNA, dictates the sequence of amino acids to be added. A number of ribosomes are attached along the length of the mRNA, each in a different stage of protein synthesis. Image courtesy of Centre for Bioscience, the Higher Education Academy, ImageBank http://www.bioscience.heacademy.ac.uk/imagebank/ (C) Dr Ijsbrand Kramer image2 messenger RNA RNA transcribed from genes that are to be translated into protein. transcription The process by which the genetic information in DNA in converted into RNA. In eukaryotic cells, the process is carried out in the nucleus. This is an additional info pop-up image images/molecule.png The picture of molecule shows a ...

DNA Manipulation

• Scientists discovered that bacteria have enzymes that can cut, or "digest" DNA. • These enzymes are known as restriction enzymes or restriction endonucleases (RE). • Restriction enzymes recognise specific sequences in DNA and then cut the DNA to produce restriction fragments. • A restriction enzyme will only cut double-helical DNA segments that contain a particular nucleotide sequence, known as the "recognition site". Image of an eppendorf tube images/centrifuge purple (Small).jpg In the 1960s, scientists discovered that bacteria have enzymes that cut, or "digest" the DNA of foreign organisms and thereby protect the cells from invaders such as viruses. Many of the procedures of molecular biology and genetic engineering rely on restriction enzymes and scientists have now isolated several hundreds of these enzymes. restriction enzymes also known as molecular scissors - enzymes that can cut the DNA at very specific sequences of several nucleotides. Different restriction enzymes recognise and cut different sequences of DNA. recognition site A nucleotide sequence - composed typically of 4, 6 or 8 nucleotides - that is recognised by and to which a restriction enzyme binds. re - did you know? In 1978, Werner Arber, Daniel Nathans and Hamilton Smith were awarded the Nobel Prize in Medicine for their discovery of restriction endonucleases. The first practical use of their work was the manipulation of Eschericia coli bacteria to produce human insulin for people with diabetes. This is an additional info pop-up image images/molecule.png The picture of molecule shows a ...

Agarose Gel Electrophoresis

• The discovery of restriction enzymes made genetic engineering possible because scientists could use them to cut DNA into fragments, which could then be analysed and used in a variety of procedures. • Agarose gel electrophoresis allows the separation of nucleic acids (such as DNA fragments) on the basis of their size and electrical charge by measuring their rate of movement through an electrical field in a gel. Agarose Gel Electrophoresis images/gel1 (Small).jpg The pattern of DNA fragments (known as DNA bands) on the agarose gel can be visualised under ultraviolet light (requires the use of ethidium bromide) or by naked eye (requires the use of Azure blue stain). Use of molecular weight markers (several DNA fragments/bands in the same lane) of known size (base pairs) allows for determination of the molecular weight (i.e. size in base pairs) of a DNA molecule/fragment of unknown size. This method also allows for estimation of DNA concentration (the brighter the band, the more DNA present). image2 agarose A powder that forms a porous gel when reconstituted with water and heated. Agarose is a highly purified version of agar that is a crude extract from red algae, one of the large seaweeds. electrophoresis A laboratory technique used to separate macromolecules on the basis of charge and size. Charged molecules migrate to one electric pole or the other with their speed, hence final location, roughly based on size. This is an additional info pop-up image images/molecule.png The picture of molecule shows a ...

Polymerase Chain Reaction (PCR)

• Polymerase Chain Reaction (PCR) is a key molecular biology technique that allows a small amount of DNA to be amplified exponentially. • With PCR it is possible to amplify a single piece of DNA across several orders of magnitude, generating millions of copies of the DNA piece (for further analysis). • A DNA polymerase is used to amplify a piece of DNA through several cycles of thermal cycling. Real-time PCR images/graph.jpg PCR is commonly used in medical and biological research labs for a variety of tasks, such as the detection of hereditary diseases, the identification of genetic profiles, the diagnosis of infectious diseases, the cloning of genes and paternity testing. Below is a diagram of a melting peak that was used to confirm PCR product identity. Each double stranded DNA has its own specific melting temperature (Tm), which is defined as the temperature at which 50% of the DNA becomes single stranded, and 50% remains double stranded. Checking the Tm of the PCR products can be compared with analysing a PCR product by length in agarose gel electrophoresis. image2 pcr Polymerase Chain Reaction - a technique that allows millions of copies of a chosen segment of nucleic acid (DNA/RNA) to be replicated accurately and efficiently in vitro (i.e. in a test tube); A method for exponentially increasing the number of copies of a specific DNA sequence. The use of PCR enables the genetic analysis of biological samples containing only tiny amounts of DNA. thermal cycling The ends of the DNA segment (template) to be copied are defined by small pieces of synthetic DNA called primers. The reaction is facilitated by a heat stable DNA polymerase (enzyme that assembles nucleotides into DNA strands in the order dictated by a template) that is able to withstand many cycles of heating and cooling involved in PCR. This is an additional info pop-up image images/molecule.png The picture of molecule shows a ...

DNA in Crime

• Forensic scientists can use DNA located in skin, blood, saliva, other bodily fluids or hair left at the scene of a crime to identify a possible suspect. • DNA profiling is a forensic technique used to identify a person by comparing his or her DNA with a given sample, such as blood from a crime scene. • The first national DNA database was set up by the United Kingdom in April 1995. In the UK, anyone arrested on suspicion of a recordable offence must submit a DNA sample to the database, which is then kept on permanent record. DNA swab images/swab2 (Small).jpg Crime scene investigators (CSIs), also known as scenes of crime officers (SOCOs), attend crime scenes to record and examine evidence. The evidence they discover is then used to investigate crimes. The police request DNA swabs from suspects in order to obtain their DNA profiles. Suspects' DNA profiles are then compared to DNA profiles generated from evidence (i.e. DNA extracted from blood, saliva etc.) found at the scene of the crime. Since there is a very small possibility that two individuals may have the same sequences, the technique is more effective at acquitting a suspect than proving the suspect guilty. image2 dna profiling In theory, a single strand of DNA is enough to establish a profile. First, the DNA sample is broken into fragments with the help of restriction enzymes, then the sample is amplified using PCR. The amplified fragments are then separated using agarose gel electrophoresis. The overall layout of the DNA fragments (or bands on the gel) is called a DNA profile. dna database A National DNA database is a database of DNA samples against which law enforcement agencies can match suspect DNA. This is an additional info pop-up image images/molecule.png The picture of molecule shows a ...

Overview

• Bioethics is the study of the ethical and moral implications of new biological discoveries and biomedical advances, as in the fields of genetic engineering and drug research. • Areas of health sciences include: Animal rights Artificial insemination Cloning Gene therapy Genetically modified food Stem cell research How far can science go? images/beaker1 (Small).jpg What do you think? image2 genetic engineering Genetic engineering refers to the scientific alteration/manipulation of the genetic material in a living organism. It involves the production and use of recombinant DNA that has been employed for instance to create bacteria that synthesise insulin; Genetic engineering is the process of manually adding new DNA in an attempt to add or modify traits in that organism. stem cells The term stem cells refers to cells that have not yet acquired a specific function. Stem cells are unspecialised or undifferentiated cells that can develop into various differentiated cell types. Description comes here Description comes here This is an additional info pop-up image images/molecule.png The picture of molecule shows a ...

Cloning

• Cloning is the process of creating an identical copy of an original. • A clone in the biological sense is a single cell (like bacteria for instance) or a multicellular organism that is genetically identical to another living organism. • Sometimes cloning can refer to "natural" clones made either when an organism reproduces asexually or when two genetically identical individuals are produced by accident (as is the case with identical twins). Molecular techniques images/eppendorf2 (Small).jpg Image of a microcentrifuge tube (also called eppendorf tube). A small but fundamental invention! image2 cloning The process of making a clone, a genetically identical copy. Cloning can refer to the technique of producing a genetically identical copy of an organism by replacing the nucleus of an unfertilized ovum with the nucleus of a body cell from the organism. natural cloning The mitotic division of a single cell to give rise to a population of identical daughter cells or clones. This is an additional info pop-up image images/molecule.png The picture of molecule shows a ...