Human Cells Revision - Cell Biology PowerPoint Slides

Human Cells Revision slides – some key topics to study Mitosis – Cell division forming 2 identical cells Some types of somatic cells divide for growth and tissue repair Each human somatic cell contains 46 chromosomes (2 sets of 23) and is diploid The nucleus divides into tw...

Human Cells Revision slides – some key topics to study Mitosis – Cell division forming 2 identical cells Some types of somatic cells divide for growth and tissue repair Each human somatic cell contains 46 chromosomes (2 sets of 23) and is diploid The nucleus divides into two new nuclei with each receiving the full complement of all 46 chromosomes i.e. the cells produced by mitosis have TWO sets of chromosomes So mitosis is a process of nuclear division immediately followed by full cell division whereby one cell divides into two genetically identical cells Meiosis – production of gametes (sperm/eggs) During meiosis, a diploid germline cell is one which divides to form the gametes (sex cells) – i.e. divide to produce sperm and eggs in humans. Meiosis allows the production of the haploid sperm and eggs. During meiosis, division of the germline cells results in 4 nuclei being produced Each new nuclei receives a single set of 23 chromosomes (i.e., it is haploid) and becomes a gamete MEIOSIS is the division of diploid germline cells to produce haploid gametes Cancer Cell division is normally controlled by the cell cycle – where the rate of cell growth and division is regulated by chemical signals. Cancer cells do not respond to regulatory signals. This results in rapid, uncontrolled division of cells. This is how a tumour can form. A tumour is a mass of abnormal cells that fails to respond to cell signals and divide too quickly. Cancer Benign tumour – discrete group of abnormal cells. Some do not cause problems and can be removed Malignant tumour – cells lose surface molecules that keep them attached to the original (primary) tumour. Allows them to spread, ‘seeding’ new (secondary) tumours – e.g. malignant melanoma; some breast cancers. DNA Nucleotides This represents one DNA nucleotide, made up of three parts – phosphate, deoxyribose sugar, and one of the four bases (adenine, thymine, cytosine, guanine). Make sure you could sketch out a nucleotide The phosphate is represented by a circle The deoxyribose sugar is represented by as pentagon shape. DNA Structure You should study the diagram of DNA structure and ensure you know which parts represent the bases, sugar, and phosphates. The sugar in DNA is called deoxyribose sugar. The bonds between bases are hydrogen bonds, which are weak bonds. The complementary base pairing rule: A bonds with T C bonds with G RNA Structure RNA nucleotides contain a phosphate group, RIBOSE sugar and one of 4 bases: A, U, C, G RNA compared to DNA Note – if comparing the structure of RNA and DNA you must mention BOTH RNA and DNA Type of RNA Function /Features mRNA Carries a copy of the DNA code from the nucleus to the ribosome. Linear molecule, with codons tRNA Each tRNA molecule carries its specific amino acid to the ribosome. Cloverleaf-shaped molecule, with anticodons rRNA RNA (rRNA) is a component of the ribosome itself (alongside proteins).  mRNA mRNA is a liner, unfolded single strand of RNA mRNA has CODONS (triplets of bases) The mRNA is produced during TRANSCRIPTION by copying the code on the appropriate gene on the DNA chromosome. The mRNA is spliced before leaving the nucleus and moving to the ribosome where it will direct the process of TRANSLATION. SPLICING Regions of a gene that code for protein are known as EXONS (they are expressing regions, or coding regions) Regions of a gene that are non-coding are known is INTRONS (they are intervening regions, or non- coding regions that don’t code for protein. The type of modification to mRNA as shown in the diagram is called SPLICING. This removes introns from the mRNA primary transcript, Simplified tRNA diagram tRNA takes amino acids to the ribosome where they are bonded together forming a polypeptide chain. tRNA has an ANTICODON (exposed triplet of bases) tRNA has an attachment site for the amino acid Translation Study the diagram and notice that each triplet of bases (codon) on the mRNA is complementary to the anticodon on the corresponding tRNA. There is no T in RNA – it is replaced by U (uracil), so complementary pairing is: A-U C–G Bonds form between amino acids – these are PEPTIDE bonds, forming a POLYPEPTIDE chain which is the first version of the protein. Single Gene Mutations Single gene mutations are caused by a change to the nucleotide sequence Can occur in 3 ways: a nucleotide is substituted, inserted or deleted This results in either a substitution, insertion, or deletion mutation as shown below. Single Gene Mutations Substitution mutations can be: Missense –one amino acid swapped is for another – creates a protein that functions in a different way. Nonsense – a stop codon is reached prematurely. So if the mutation causes a stop codon to be reached early, the polypeptide chain formed with be shortened and does not function. Splice site mutations – some introns retained or some exons not retained in mature transcript  Types of chromosomal mutations Chromosome structure mutations cause substantial changes to the chromosome. You should be able to accurately describe (briefly) the different types of chromosomal mutation: Deletion – part of one chromosome is removed Duplication – a section of a chromosome is added from its homologous partner Translocation - deleted part from one chromosome attaches itself to a non-homologous chromosome Inversion – a section of a chromosome is reversed (chromosome breaks in 2 places, segment turns round before rejoining).  Human genomics Genomics is the study of the human genome. The genome of an organism is the entire hereditary information encoded in DNA. The genome consists of genes and other DNA sequences that do not code for proteins. Genomics has the potential to allow a more personalised approach to medicine and prescribing drugs, with the use of two important areas of biology, bioinformatics and pharmacogenetics Bioinformatics Bioinformatics is an area of biology that uses a mixture of computer technology, molecular biology and statistical analysis. Genomic sequencing produces huge amounts of data which is analysed by computers. With bioinformatics, the sequence of a person’s DNA is identified and analysed. Bioinformatics has allowed great advances in genomics over recent years (information on genomic sequences gathered in days /weeks rather than years). Pharmacogenetics Pharmacogenetics involves the study of the effects of pharmaceutical drugs on members of the human population based on genomic information The population is genetically diverse The effects of the drugs can be therapeutic, neutral or adverse So, pharmacogenetics allows use of a person’s genome information to help doctors decide which medicines to prescribe Use of pharmacogenetics allows a more personalised approach to medicine a person may be prescribed the most effective drug for their condition there may be less chance of side effects or adverse reactions PCR –polymerase chain reaction PCR is the amplification of a DNA fragment. The term amplification of DNA means to make many copies (millions of copies) of the strand. There are 3 temperatures per single cycle of PCR: 92-98°c to ‘melt’ the DNA by breaking the hydrogen bonds between strands. 50-65°c to allow the primers to anneal (bind) to their complementary regions on the two DNA strands. 70-80°c to allow the Taq polymerase to work on building the new strand (as we saw in DNA replication). After each cycle, the quantity of DNA will have doubled. PCR Heat tolerant DNA polymerase is used in the 3rd stage where it adds new nucleotides creating a new strand. Remember that DNA strands can only extend in one direction (whether in cells during DNA replication, or in the lab during PCR). Strands extend in the 5’ -3’ direction which means that new nucleotides are added at the 3’ end. Metabolic pathways Metabolic pathways Catabolic – break down of complex molecules to simpler ones, releasing energy Anabolic – building up more complex molecules, using up energy. So, if a metabolic pathway releases energy, it is catabolic, and if a pathway requires energy, it is anabolic.  Regulation of metabolic pathways Sometimes products of a pathway build up to levels that inhibit an earlier stage in the pathway and cause the pathway to halt until levels reduce. An example is regulation of the respiratory pathway Glycolysis is regulated by increased levels of ATP & citrate As shown in the diagram when ATP levels get too high, they inhibit phosphofructokinase so the subsequent stages of the pathway would not take place until ATP levels reduce again.  Inhibitors Inhibitors decrease the rate of enzyme-controlled reactions Competitive inhibitors Compete with substrate for the active site and prevent the substrate from binding to the active site Non-competitive inhibitors Bind to an area other than the active site (non-active (allosteric) site). This alters the enzyme shape, and therefore the active site shape, so that the substrate can no longer bind to the active site  Aerobic Respiration Three stages to aerobic respiration Stage 1: Glycolysis – occurs in cytoplasm of cell Stage 2: Citric Acid Cycle – occurs in matrix of mitochondrion. Oxygen is required for this to occur. Stage 3: Electron transport chain – occurs on cristae of mitochondrion. Oxygen is required.  Make sure you can recognise an interpret a diagram of the aerob Aerobic Respiration respiration pathway. What happens during stages 1 and 2? Stage 1: Glycolysis – glucose is converted to pyruvate; a net gain of 2 ATPs Stage 2: Citric Acid Cycle - citrate (formed by Acetyl Co A combining with oxaloacetate) is converted into intermediate products by removal of carbon and hydrogen. Carbon combines with oxygen forming carbon dioxide which diffuses out of the cell. Hydrogen is removed from the substrate by dehydrogenase enzymes. Hydrogen then combines with the coenzyme NAD which becomes NADH. The role of NAD is to transport the hydrogen ions and electrons to the Electron Transport Chain.  Stage 3 - Electron Transport Chain (ETC) Stage 3, the ETC reaction, occurs on the cristae of the mitochondria. The ETC is a group of proteins, including an enzyme called ATP synthase, embedded in the inner mitochondrial membrane Hydrogen ions are pumped across this membrane. The hydrogen ions then flow back across the membrane via a protein called ATP synthase. As they do this ADP is bonded to Pi producing ATP The hydrogen ions then combine with electrons and oxygen forming water (H2O). So, the products of the ETC are ATP and water. Stage 3 - Electron Transport Chain  The electron transport chain This is one way to represent the ETC. Many ATP molecules are produced as the hydrogens are passed along the carrier proteins in the membrane. he ETC is the stage of aerobic respiration where most of the ATP is m Energy systems in muscle cells Structural features Command words Command words in the question – pay attention to these. What are you being asked to do? Compare – you must specifically discuss both sets of data – what is the difference between them? Is one data set greater than the other? Name – just the name needed, may be one or a few words Describe – need a sentence with information describing it. If two marks are available, then 2 sentences/ pieces of information are required. Calculating percentage increase To calculate a percentage increase, use the formula: Percentage increase = EXAMPLE: if something increased from 30 units up to 40 units: The actual increase is 10, the starting value is 30, so the percentage increase is 10/30 x 100 = 33.3% Graphs Graphs at level 6 can be tricky. Look out for graphs with two Y axes. It may be useful to bring highlighter pens and highlight the axis label and appropriate data line in the same colour. The two Y axes will have different scales so take care to work out what each box on the grid represents for each. Be precise when reading from a graph.