Science Subject Selection Notes PDF

Term 3: DNA and Genetics Chromosomes: Thread like structures in the nucleus composed of DNA and proteins, contains genetic information in the forms of genes. Contemporary base pairs: a pair of bases that join together to make the rungs of the DNA ladder, aden...

Term 3: DNA and Genetics Chromosomes: Thread like structures in the nucleus composed of DNA and proteins, contains genetic information in the forms of genes. Contemporary base pairs: a pair of bases that join together to make the rungs of the DNA ladder, adenine, thiamine, cytosine and guanine. Deoxyribonucleic acid: a double helix made of nucleotides, the molecules that determine the genetic characteristics of the most living things. Deoxyribose sugar: one of the pairs that make up the nucleotide. Gene: a section of the DNA that carries genetic code for particular characteristics. Nitrogen rich base: part of nucleotide the four types are adenine, thiamine, cytosine, guanine Nucleotides: the building blocks of DNA, composed of deoxyribonucleic acid, phosphate groups and nitrogen rich base. Phosphate group: one of the pairs that make up the nucleotide. Autosomes: all the chromosomes in a cell other than the sex chromosomes. Centromere: the point on the chromosome where the two chromatids join together. Chromatid: one of the strands of a chromosome following replication. Diploid number: the number of chromosomes in body cells: two sets of 2N. Gametes: sperm and egg cells. Haploid number: the number of chromosomes in gametes: one set or N. Homologous chromosomes: chromosomes with genes for particular characteristics at the same location. Meiosis: the type of cell division that produces gametes with half the number of chromosomes of the parent cells. Mitosis: the type of cell division that produces two daughter cells identical to the parent cell. Replication: the process of making copies of DNA. Sex chromosomes: the chromosomes that determine the sex of an individual. Allele: different forms of the same gene located at the same point of the homologous chromosome. Dominant allele: allele for the traits that is observed in the outward appearance of an individual Genotype: genetic information carried by an individual. Heterozygous: having two different alleles on homologous chromosomes. Homozygous: having two identical alleles on homologous chromosomes. Mutation: a mistake that happens in the DNA is copied, causing a change in the base sequence. Phenotype: observable characteristics of an individual; the way the genotype is expressed. Pure breeding: where all individuals have the same genetic information for a characteristic generation after generation. Recessive allele: allele is the trait that remains hidden in the heterozygous condition. Sex linked genes: genes present on the sex chromosomes. Gene splicing: the process used to add a gene into or remove genes from DNA. Gene therapy: the process of replacing a defective gene with a normal gene. Genetically modified: having the genes changed. Genome: the genetic information carried by a haploid set of chromosomes. Human genome project: an international project that aims to identify all the human genes and determine the sequence of the base pairs that make up the human chromosome. Plasmid: ring of the DNA found in the bacteria. Recombinant DNA technology: technology that allows DNA to be recombined with other genes. Single nucleotide polymorphisms ( SNP’s): differences of only one base between one human and another. Adult stem cells: cells that can make certain types of body cells Biotechnology: use of organisms or parts of organisms in processes to make or change predictions. Embryonic stem cells: cells found in the embryo that are pluripotent Induced pluripotent skin cells (iPCS): skin cells that can be induced to become stem cells In-vitro fertilization: the process of fertilizing eggs outside the human body then placing the developing embryo back into the woman's uterus. Pathogen: a disease causing organism Pluripotent: capable of becoming any one of the 220 different cell types found in the human body. All living things have genetic information stored in large molecules called DNA (deoxyribonucleic acid). DNA is stored in the nuclei of cells, where it is packaged into thread-like structures called chromosomes. The order of the subunits that make up DNA molecules encodes the genetic information of an organism  DNA molecules are made up of subunits called nucleotides. Nucleotides consist of three parts – a sugar, a base and a phosphate. The sugar molecule is in the center, with the phosphate attached to one side and the base attached to the other.  The sugar in nucleotides is called deoxyribose, which is why the full name for DNA is deoxyribonucleic acid. All nucleotides in DNA contain the same sugar and phosphate, but there are four different bases, and consequently four different nucleotides. The four bases are guanine, cytosine, adenine and thymine, but these are usually just referred to by their first letter – G, C, A and T respectively. Since nucleotides differ only in their type of base, they are also referred to by the letters G, C, A and T. DNA molecules consist of nucleotides that are joined in two ways – firstly, to form a single strand of DNA, and secondly, to form a double strand of DNA. Single-stranded DNA is formed when nucleotides are joined by a type of covalent bond known as a phosphodiester bond. These bonds form between the sugars and phosphates of adjacent nucleotides, creating what is referred to as the sugar-phosphate backbone of DNA.  Double-stranded DNA is formed when nucleotides are joined by a type of bond called a hydrogen bond. These bonds form between the bases of nucleotides on each strand. The two strands are aligned in opposite directions, which is referred to as antiparallel orientation. Hydrogen bonds are not full chemical bonds, but are formed due to electrostatic attraction between slightly positive and slightly negative regions of DNA. Therefore, hydrogen bonds are weaker than covalent bonds, which allows the two strands of DNA to separate during processes such as DNA replication and gene expression.  The hydrogen bonding between bases on different strands of DNA is known as base-pairing. Base-pairing only occurs between specific combinations of bases, hence it is often referred to as complementary base-pairing. The bases G and C always pair together, forming a G-C pair. The bases A and T always pair together, forming an A-T pair. These are known as the base-pairing rules.  Once joined, the two strands of DNA twist around each other, forming a structure known as a double helix. This resembles a twisted ladder, where the ‘rails’ consist of alternating sugars and phosphates, and the ‘rungs’ consist of base pairs.  The order of the four different nucleotides in DNA molecules, known as a DNA sequence, determines the genetic make-up of an organism. This ‘genetic code’ is the same for all organisms. Therefore, DNA differentiates not only individuals of a species, but all living things on Earth. The genetic code works in much the same way as the 26 letters of the English alphabet, which code for all the English-language books that exist. The process of copying DNA is known as DNA replication.  The first process that occurs is when the DNA unwinds itself An enzyme called DNA helicase unwinds the double helix, so the 2 strands are separated. This happens at several points during the DNA  Then an enzyme called DNA polymerase attaches itself to the DNA strands, and is used to add complementary free nucleotides to the now exposed bases. This now forms two DNA molecules, each of which consists of 1 brand new stand and one original DNA. These two strands then combine to form a double helix. Why is DNA described as the universal code? DNA is described as the universal code as it codes for cell production/reproduction in the world What is the molecular function of a gene? Gene codes for protein Cell division There are two types of cell division: Mitosis : produces two daughter cells that are identical to the parent cell. This is the type of cell division involved in growth and repair of the body. Meiosis: produces gametes (eggs and sperm) that have half the number of chromosomes of the parent cell Mitosis - why does it occur? Growth and Development: In multicellular organisms, mitosis is the process that enables growth from a single fertilized egg to a fully developed adult. By producing new cells, mitosis allows an organism to grow and develop its tissues and organs. Repair and Regeneration: Mitosis is essential for repairing damaged tissues and replacing worn-out or dead cells. For example, when you get a cut on your skin, mitosis generates new cells to heal the wound. Asexual Reproduction: In many single-celled organisms, mitosis is the method of reproduction. The organism duplicates its genetic material and divides into two identical daughter cells, each a clone of the original. Maintaining Genetic Stability: Mitosis ensures that each daughter cell receives an exact copy of the parent cell's DNA. This genetic consistency is crucial for maintaining the organism's characteristics and functions across generations of cells. Steps involved in the process of mitosis I - interphase P - prophase M - metaphase A - anaphase T - telophase Step 1 : interphase  1. The chromosomes replicate to become double stranded Step 2 : prophase 1. Double stranded chromosomes become visible Step 3: metaphase 1. Double stranded chromosomes line up along the equator of the cell Step 4: anaphase  1. The chromosomes move to opposite ends of the cell Step 5: telophase 1. Two nuclei form, each with the same number of chromosomes as the parent cell. Step 6: cytokinesis 1. Membranes form, separating the two nuclei into two daughter cells (diploid cells) Gametes: Gametes are the sex cells Eggs produced in the ovaries of the female reproductive system Sperm produced in the testes of the male reproductive system The other chromosomes are not sex chromosomes - they are known as autosomes Grouped into 22 pairs The chromosomes in the pairs are homologous Homologous chromosomes Are the same length  Have the centromere ( the point where the two chromosomes joins ) in the same position Have genes for particular characteristics at the same location along the length Gametes have half the number of chromosomes known as haploid number Meiosis: Meiosis if the process that produces gametes ( sex cells, sperm and eggs) Chromosomes replicate like they do in mitosis but slight differences at the end - they end up with only N23 chromosomes Meiosis process x2 I - interphase P - prophase M - metaphase A - anaphase T - telophase / cytokinesis Sexual reproduction Sexual reproduction creates a variation in a population. It is the role of the male and female reproductive systems to ensure: The female and male gametes meet Fertilization takes place The new individual has the best chances for survival Female reproductive system Ovary: releases eggs (ova) and produces the female sex hormones estrogen and progesterone Cervix: The small opening to the uterus. The cervix stretches during childbirth. During sexual intercourse, the penis does not enter the cervix or the uterus Vagina: the penis is inserted here during sexual intercourse. Sperm must swim from here to the fallopian tube if fertilization is to occur Uterus : the fertilized egg implants itself in the lining of the uterus to continue growing. The baby develops and grows here for the nine months of the pregnancy Fallopian tube (oviduct): tubes connecting ovaries to the uterus. Fertilization occurs here. Male reproductive system Uterus: deliver urine from the kidneys to the bladder Bladder: stores urine Sperm duct (vas deferens): connects testes to the penis Penis: contains sponge-like tissue that fills with blood when the male is sexually aroused. The tissue expands and is harder than before, causing an erection. Testicles or testes: made up of tiny, tightly coiled tubes called seminiferous tubules in which sperm form and mature. Testes also produce the male sex hormone testosterone Epididymis: coiled up tubes at the top of the testis in which sperm are stored Prostate gland (cowper's gland): adds fluid to the sperm to make it semen. Urethra: tube running the length of the penis. It empties the bladder or urine and allows the passage of semen Scrotum: sac holding the testes Punnett squares An individual that is heterozygous produces gametes of two types. Half the gametes carry a dominant allele. The other half of the gametes carries a recessive allele. Genotypes and Phenotypes Genotypes - the actual genetic information carried by an individual Phenotypes - the observable characteristics of the individual Sex linkage Some genes are found on the sex chromosome, these are called sex linked gene X chromosomes is longer than the Y chromosome and thus tends to carry more Always X chromosomes are responsible for genes and traits Nature of genetic disorder Unique characteristics  Y-linked As biological males (XY) only have a single Y chromosome, disorders on this chromosome will always be expressed. As biological females (XX) lack a Y chromosome, they cannot have a Y-linked genetic disorder X linked If present in males, these disorders will always be expressed as only one X chromosome is present. Females can be carriers of these genetic diseases and must be homozygous recessive for this disorder to be prevalent Example of sex linked gene Red-green colorblindness gene is carried on the X chromosome Normal vision is depicted as N which is the dominant trait and color blindness as a n. Hemophilia Description of hemophilia - Hemophilia is a genetic bleeding disorder where the blood doesn't clot properly due to a deficiency in one of the clotting factors. This deficiency leads to prolonged bleeding after injuries, spontaneous bleeding, and potential complications in joints and muscles. It is an X-linked recessive disorder, primarily affecting males, while females are typically carriers. Treatment involves replacement therapy with clotting factor concentrates to prevent or control bleeding episodes. Though there is no cure, proper management and regular treatment can help individuals with hemophilia lead normal lives. Gender - hemophilia primarily affects men, but women can have hemophilia too. Symptoms - Unexplained and excessive bleeding from cuts and joints Many large or deep bruises Unusual bleeding after vacation Pain, swelling, tightness in your joints Blood in your urine or stool Nose bleeds without a common cause Life expectancy - The life expectancy of people with hemophilia is now similar to that of the general population Treatment for hemophilia - Replacement Therapy: This is the main treatment for hemophilia. It involves regular infusions of clotting factor concentrates to replace the deficient factor in the blood. Desmopressin (DDAVP): This synthetic hormone can stimulate the release of stored Factor VIII in mild cases of Hemophilia A.  Antifibrinolytic Medications: Drugs like tranexamic acid and aminocaproic acid help prevent clots from breaking down, which can be useful in combination with replacement therapy. Gene Therapy: This is an emerging treatment option that aims to provide a long-term solution. It involves introducing a functional copy of the gene responsible for producing the missing clotting factor. While still under study, gene therapy has shown promise in reducing bleeding episodes and the need for replacement therapy. Fragile X syndrome Description of Fragile X syndrome - Fragile X syndrome is a genetic disorder caused by a mutation on the X chromosome, specifically in the FMR1 gene. This mutation leads to a deficiency or absence of the fragile X mental retardation protein (FMRP), which is essential for normal neural development. The syndrome is characterized by intellectual disability, behavioral challenges, and distinctive physical features such as a long face, large ears, and a prominent jaw. It can also include symptoms like anxiety, hyperactivity, and sensory sensitivity. Fragile X syndrome affects both males and females, but males typically exhibit more severe symptoms due to having only one X chromosome. As an inherited condition, it is passed down through families, often with varying degrees of severity. Gender -. This is because males have only one X chromosome, so the presence of a mutation in the FMR1 gene on their single X chromosome leads to a lack of the fragile X mental retardation protein (FMRP). Females, on the other hand, have two X chromosomes, so they may still have some FMRP from the normal copy of the gene on their other X chromosome, which can result in milder symptoms or, in some cases, no symptoms at all. Therefore, while the syndrome can affect both genders, the severity and presentation can vary, with males often experiencing more pronounced intellectual disability and behavioral challenges. symptoms - intellectual disability and learning difficulties Delayed development of nonverbal communication, language processing, and speech Physical features such as large ears, long face, and flat feet Behavioral challenges such as anxiety, hyperactivity, and autism Sensory issues such as sensitivity to noise, light, and touch Life expectancy - People with Fragile X syndrome generally have a normal life expectancy, as the condition itself does not typically affect the lifespan. Possible cure or treatments Behavioral Therapy: This includes strategies like Applied Behavior Analysis (ABA) to help manage behavioral issues, such as hyperactivity, anxiety, and social interaction difficulties. Therapy can be individual or group-based, focusing on communication, social skills, and adaptive behaviors.  Speech and Language Therapy: Many individuals with Fragile X syndrome experience speech and language delays. Speech therapy can help improve communication skills and address specific issues like articulation and language comprehension. Occupational Therapy: Occupational therapists work with individuals to develop fine motor skills, improve daily living activities, and manage sensory processing issues, which are common in people with Fragile X syndrome. Medications: There is no medication specifically for Fragile X syndrome, but certain drugs can help manage symptoms such as anxiety, hyperactivity, mood swings, and aggression. These may include antidepressants, stimulants, and antipsychotic medications, depending on the individual's needs. Pedigree charts An ancestral line/chart depicting the lineage or descent of an individual Chromosomal abnormalities Sometimes mistakes happen during meiosis when the sex cells are being produced and the information passed on to the next generation is changed. If the chromatids fail to separate during meiosis, the child will be born with an extra chromosome or part of a chromosome. - This is called chromosomal abnormality Examples include: Down syndrome and Klinefelter syndrome Mutations Mistakes can happen as the DNA is being copied. The base sequence is changed and mistakes occur in the manufacture of proteins. - This type of change is called mutations Mutations can occur in either somatic cells or gametes. If the mutation occurs in a somatic cell it can result in the development in cancer If the mutation arises within a gamete it is called a germline mutation, these can contribute to the genotype of the zygote and thus affect every cell in the produced organism. Mutations can occur spontaneously but can also be induced by a range of different factors, some of which are outlined in the following table. Radiation Chemical Biological UV rays Cigarette smoke H. pylori bacteria X-rays Arsenic Hep C virus Radioactive Asbestos Human papillomavirus substance Ultimately, a gene will encode a specific protein. Thus a mutation in a specific gene will cause a mutated protein to be produced  Subunits of proteins are amino acids Types of mutations Silent mutations - are changes in the genetic code that do not affect the individual Missense mutation - are changes that don’t stop the gene from making protein. The protein may not correctly function and cause a disease. A missense mutation is responsible for sickle cell anemia. Nonsense mutations - are more significant types of mutation. The mutation causes the cell to stop reading the information on the gene before its end Frameshift mutations - are caused by the insertion or deletion of a single base. Frameshift mutations frequently result in severe genetic diseases such as Tay- Sachs disease Mutations add to the diversity of organisms, Natural selection works on this diversity by selecting the individuals most suited to an environment. Genetically modified organisms In genetically modified organisms, the genetic information is changed by inserting a new gene. Genes are then copied to all daughter cells when the parent cell divides by mitosis. These modified cells will mature into a completely new strain of organisms Using genetic modification, desirable traits such as insect resistance and increased nutrient value are added to the plant Technology benefits but also causes controversy Examples of GM organisms Canola Rice Golden rice 2 is genetically modified using the genes from daffodils, corn and bacteria Rice contains beta carotene - the chemical that give carrots their orange color and which the body converts into vitamin A Developed for countries where blindness due to vitamin A deficiency was high However significant opposition from environment and anti globalization groups so it is still grown for research not human consumption Gene splicing It is the process by which DNA of an organism is cut and a gene, perhaps another organism is inserted Gene splicing is often used in the industry to allow single celled organism such as bacteria to produce useful products such as human insulin Bacteria have DNA in chromosomes, but they also have special ring structures of DNA called plasmids. Using enzymes, these plasmids can be cut open and spliced  The technology of combining DNA from different genes is called recombinant DNA technology The process of gene splicing is as follows 1. Plasmids are removed from bacterium 2. Plasmids are cut using an enzyme 3. DNA is removed from the human cell 4. DNA is cut using an enzyme to isolate the desired gene 5. The desired human gene is inserted into the plasmid to form recombinant DNA 6. The recombinant DNA is put into a bacterium 7. Bacterial cells grow and divide to produce many copies of the introduced gene  The total collection of genes in an organism is called its genome Human genome project aimed to Identify all 20 000-25 000 genes in the human genome Determine the sequence of the 3 billion base pairs that make up the human chromosomes All human share about 99.9% of their DNA however scientist have identified million of locations that differ by only one base from one human to another These differences are known as single nucleotide polymorphisms (SNP’s) Pros Cons Successfully identified where the genes of the 15 years DNA are located in the body Genetically modified foods $3 billion Make crops grow faster and more resistant to Requires skills pesticides Genetic testing Gene or genetic testing is when a lab checks your genes for variations or mutations Once genes are known scientist can test for that gene 400 genetic test are available in Australia People use the test for a variety of reasons Knowledge of genetic makeup could help you avoid the disease by controlling your lifestyle Some test include heart disease and type 2 diabetes Gene testing also can tell people if they are carrying a specific disease causing gene that could be passed onto their children Cystic fibrosis, thalassemia and Hungtington disease are examples of genetic diseases which can help people make decisions Genetic testing detects a particular problem gene and predict the severity of it Genetic testing can be used to diagnose genetic disorders in fetuses for example Down syndrome is the result of having an extra chromosome in the 21st pair Turner syndrome is caused when a female only has one X chromosome Fragile X syndrome is the most common inherited cause of mental retardation Other uses of genetic testing include Identification of a suspect in a criminal investigation  Testing to identify biological 1 parents Analysis of DNA for donor and recipient for organ transplantation ‘How does genetic testing affect us? Knowledge of gene could affect a person’s ability to get life insurance, cover this could affect the whole family If a disease is found it could run in the family - family members need to decide to get tested or not Gene therapy Gene therapy aims to fix a faulty gene or replace it with a healthy gene to try to cure disease or make the body better able to fight diseases Cystic fibrosis is a common genetic disease where scientist are trying to isolate the CFTR gene and transfer it to a normal gene into the lungs but they have not been successful. Treating cancer Cancerous tumors are fed by uncontrolled growth and abnormal blood vessels In 2008, medical research institute found they could switch off the gene This reverses the blood flow into the tumor Scientist are hoping this will lead to the death of the tumor Development of Vaccines Bacterial diseases are a major threat to health worldwide (tetanus, whooping cough, diphtheria) Diphtheria - an infection of the local tissue of upper respiratory tract with production of toxins which causes systematic effects on heart and peripheral tissue Vaccines were developed to help stop the spread of infectious diseases which led to death Vaccines work by causing your body to provoke an immune response to react as if it has been infected by a pathogen Traditional vaccines are taking small amounts of poison produced by the bacteria and make it inactive os use dead bacteria Your body responds by making antibodies - immunity Genome vaccines Bacteria contain various proteins on their surface Some of these proteins will start to make your body produce antibodies Vaccines can be produced by using one of these proteins Step in making vaccines using genomes 1. Scientist identify the genetic code that causes the surface proteins to be produced 2. Analyze the surface proteins and identify which ones will cause the body to produce antibodies 3. Genes for these proteins are isolated then spliced into a plasmid of bacterium E.coli found in human intestine 4. Grown in laboratory E coli produced proteins coded by genes splicing 5. The ones that produce large quantities are purified and tested on mice 6. Blood of mice is analyzed for antibodies 7. Proteins that caused the greatest antibody production are further tested 8. Finally, two or three proteins go into human trials Stem cells Stem cells are a type of cell that can help with growth and repair of your body tissue They can be found in bone marrow, as well as amniotic fluid and the blood in umbilical cords When an embryo is a few days old, it contains cells that are pluripotent Pluripotent cells can become any of the 220 different cell types found in the human body - these are known as embryonic stem cells In the late stage, the cells have differentiated and become fixed as skin cells, cardiac muscle cells or nerve cells in the brain Some cells have the capability to continue to divide to make new cells heal wounds or replace worn out cells Adult stem cells Adult stem cells were discovered when scientist began to experiment with bone marrow for use in leukemia treatment Adult stem cells allow you to regenerate and repair your tissue