BIO101/FSC111 Lecture Slides - Dr Fakorede PDF

1 BIO101 – General Biology/ FSC111 – Introductory Biology Concepts of Biology and Scientific Inquiry S. Taiwo Fakorede, Ph.D. Department of Cell Biology and Genetics University of Lagos, Nigeria U N I V E...

1 BIO101 – General Biology/ FSC111 – Introductory Biology Concepts of Biology and Scientific Inquiry S. Taiwo Fakorede, Ph.D. Department of Cell Biology and Genetics University of Lagos, Nigeria U N I V E R S I T Y O F F I R S T C H O I C E A N D T H E N AT I O N ’ S P R I D E Learning Objectives 22 At the end of this study session, you should be able to: define biology in scientific sense describe the characteristics of life understand the relationship between structure and function demonstrate the ability to formulate hypothesis, design experiments, analyze data, and draw valid conclusions based on evidence  3 What is Biology/Life? What is Biology? 4 The study of life The science of life Biology is the scientific study of life Biologists study life in all its forms, including the study of single cells to the global interactions of millions of organisms. What is Life? 5 Biologists created a list of characteristics that living things have Biologist consider an object to be alive if, and only if, it displays ALL of these properties Characteristics of Life 6 1. Cells - all living things are made up of cells 2. Order - living things are complex and ordered 3. Sensitivity or Response to Stimuli - respond to their environment 4. Reproduction - reproduce their own kind to keep the species alive 5. Adaptation - environment influences survival 6. Growth & Development - can grow and develop (change) throughout life 7. Regulation - coordination of internal functions 8. Homeostasis - maintain internal balance 9. Energy Processing - perform metabolism Characteristics of Life 7 Response to Order the environment Evolutionary adaptation Reproduction Regulation Energy processing Growth and development Levels of Organization of Living Things 8 As already mentioned, living things are highly organized and structured The atom is the smallest and most fundamental unit of matter It consists of a nucleus surrounded by electrons A molecule is two or more atoms held together by a chemical bond Macromolecules is large molecule formed by combining smaller units called monomers Levels of Organization of Living Things 9 Molecules come together with other molecules to form organelles, small structures the exist within cells and perform specialized functions The cell is life’s fundamental unit of structure and function All living things are made up of cells Levels of Organization of Living Things 10 Cells combine to make tissues, a group of similar cells that carry out the same function Organs are collections of tissues grouped together based on a common function Organ System consists of functionally related organs Organisms are individual living entities Classification of Organisms 11 Organisms can be classified by the types of cells they are made up of: Prokaryotes - single-celled organisms that do not have a membrane-bound nucleus nor organelles surrounded by a membrane e.g. Bacteria Eukaryotes - organisms with cells that do have a membrane-bound nucleus and other membrane-bound organelles e.g. Plants, Animals and Fungi Levels of Organization of Living Things 12 A population is all the individuals of a species living within a specific area A community is the set of populations inhabiting a particular area A ecosystem consists of all the living things and abiotic (non-living) things in a particular area The biosphere is the collection of all ecosystems and it represents the zones of life on Earth, includes land, water, and portions of the atmosphere Organization of Life? 13 The Biosphere Ecosystems Communities Organism Population Copyright © Campbell Biology 2016 Pearson Organization of Life? 14 Organs Tissues Cells Atoms Organelles Copyright © Campbell Biology 2016 Pearson Molecules  15 Unifying Themes of Biology Unifying Themes of Biology 16 Unifying themes connect concepts from many fields of biology In biology, themes are ideas that come up time after time – Cells – Systems – Structure and Function – Emergent Properties – Reproduction and Inheritance – Homeostasis – Interactions – Evolution Unifying Themes of Biology 17 1. Cells are the basic structural and functional units of life Two distinct groups of cells exist – Prokaryotic cells – Simple and small – Bacteria are prokaryotic – Eukaryotic cells – Possess organelles separated by membranes – Plants, animals, and fungi are eukaryotic Prokaryotic cell 18 Eukaryotic cell DNA (no nucleus) Membrane Nucleus (contains DNA) Organelles Unifying Themes of Biology 19 2. All levels of life have systems of related parts A system is an organized group of interacting parts These parts work together to make a whole Examples of systems in biology: – A single heart cell – Reproductive system, Nervous system, Digestive system, etc, all these make up the body system. – Ecosystem = forest and a desert, includes interacting living and nonliving things. Unifying Themes of Biology 20 3. Structure and function are related in biology Structure determines function. The structure is the shape or form of the object. The function is the object’s specific role. – What something does in an organism is directly related to its structure or form. – The structure of different cells differs because they perform different tasks in the body. Copyright © Campbell Biology 2016 Pearson Unifying Themes of Biology 21 4. In life’s hierarchy of organization, new properties emerge at each level Life’s levels of organization define the scope of biology Life emerges through organization of various levels With each step upward in organizational level, novel properties emerge (called emergent properties) as a result of interactions among components at lower levels For instance, an organism can achieve more than what individual cells could achieve.  Biosphere 22 Ecosystem Florida coast Community All organisms on the Florida coast Population Group of brown pelicans Organism Brown pelican Spinal cord Organ system Nervous system Brain Organ Nerve Brain Tissue Nervous tissue Cell Nucleus Atom Nerve cell Organelle Nucleus Molecule DNA Unifying Themes of Biology 23 5. Reproduction and Inheritance All organisms produce new organisms like themselves by transmitting hereditary information to their offspring via reproduction. Hereditary information is encoded in the DNA DNA → RNA → Protein The inheritance of genetic material through reproduction explains the continuity of life Copyright © Campbell Biology 2016 Pearson Unifying Themes of Biology 24 Reproduction and Inheritance Continuity of life is based on heritable information in the form of DNA DNA is the genetic material that carries biological information from one generation to the next Unifying Themes of Biology 25 6. Homeostasis Homeostasis is the maintenance of constant internal conditions. Organisms must maintain homeostasis to survive in diverse environments. Copyright © Campbell Biology 2016 Pearson Unifying Themes of Biology 26 6. Interactions - Interdependence of Organisms From molecules to ecosystems, interactions are important in biological systems At any level of the biological hierarchy, interactions between the components of the system ensure smooth integration of all the parts, such that they function as a whole. The branch of biology that studies the interactions between organisms and their environments is ecology. Unifying Themes of Biology 27 Interactions of an African acacia tree with other organisms and the physical environment Copyright © Campbell Biology 2016 Pearson Unifying Themes of Biology 28 7. Evolution – the core theme of biology Evolution is the change in living things over time. – The genetic makeup of a population of a species changes. – Evolution can occur through natural selection of adaptations. – Adaptations are beneficial inherited traits that are passed to future generations. Copyright © Campbell Biology 2016 Pearson Unifying Themes of Biology 29 Evolution – the core theme of biology Evolution accounts for both the unity and the diversity of life. Copyright © Campbell Biology 2016 Pearson  30 Methods of Inquiry in Biology Scientific Method 31 Biologists use the Scientific Method to study the living world The Scientific Method is a formal set of rules for forming and testing hypothesis The Scientific Method is a logical problem- solving system that scientists use to conduct research This Method also has very practical use in everyday life. Scientific Inquiry 32 Scientists use two methods of logical thinking to try to understand and explain the world Inductive reasoning - arriving at a general conclusion based on repeated observations Deductive reasoning - a form of logical thinking that uses a general principle or law to forecast specific results Scientific Inquiry 33 ▪ Two approaches are used to understand natural causes for natural phenomena: – Discovery/Observational science—uses verifiable observations and measurements to describe natural phenomena (e.g., fossil record, astronomy, etc.) – Hypothesis-based/Experimental science—uses the data from discovery science to explain natural phenomena. – This requires proposing and testing hypotheses Discovery Science 34 Accurate Observation: directly or indirectly Accurate Data: qualitative or quantitative ❖ Inductive reasoning ❖ Understanding nature Hypothesis-based science 35 Accurate Observation Questions Hypothesis Prediction Experiment (controlled) Hypothesis-based science 36 Data Collection & Analysis Results Deductive Reasoning Conclusion  37 Copyright © Biology 11th Ed. McGraw Hill The Scientific Methods: Observation 38 An Observation can be defined as "seeing" something (with the eyes) or a new idea that comes by reasoning It can also be recognition of an unexplained situation or problem The Scientific Methods: Hypotheses 39 A HYPOTHESIS is a testable explanation for a natural phenomenon/observation Hypotheses are: formed based on observation “rejected” or “accepted”, NEVER “proven” testable and falsifiable guide the design of experiments The Scientific Methods: Hypotheses 40 A HYPOTHESIS is a testable explanation for a natural phenomenon/observation Hypotheses are: formed based on observation “rejected” or “accepted”, NEVER “proven” testable and falsifiable guide the design of experiments The Scientific Methods: Testing Hypotheses 41 ✓ Explore a phenomenon & make observations ✓ Construct a question to investigate based on your observations ✓ Construct a hypothesis ✓ State a prediction based on the evidence ✓ Plan and test the hypothesis with an experiment ✓ Analyze the data and evidence ✓ Form a conclusion based on your results and construct new knowledge ✓ Was the hypothesis rejected or accepted/supported? ✓ Form an explanation (model) based on your conclusions and supporting evidence ✓ Connect your new knowledge to your prior knowledge and the knowledge of others (existing theories) ✓ Consider follow-up questions for investigations The Scientific Methods: Experiment 42 Experiments and further observations are exercises designed to test the hypothesis or predictions made by the hypothesis This is usually considered the data collection step Where possible experiments should contain a control group Variables in experiments 43 Hypotheses are tested experimentally, and experiments contain variables: Independent Variable (IV) - the factor being manipulated by the researchers. Dependent Variables (DV) – the outcome being measured or recorded that is predicted to be affected by the independent variable Standardized Variables (SV) - all other factors that remain constant Variables in experiments 44 Independent vs Dependent Variable Effect of room temperature on test scores. INDEPENDENT VARIABLE DEPENDENT VARIABLE temperature test scores Cause Effect Manipulated Measured X-axis Y-axis Control experiment 45 Every experiment should include a test in which the IV is set to zero or some default value, a test referred to as a control The control group goes through all the steps of an experiment but lacks the factor (not exposed to the factor) that is being tested This sort of test is also called a negative control Positive controls (tests that give a known positive result) are also appropriate for some experiments. - Experimental controls provide a reference for comparison, in addition verifying that the experimental results are reliable The Scientific Methods: Conclusion 46 The results of ‘Observations and Experiments’ are analyzed and a conclusion reached The conclusion is either the rejection or acceptance of original hypothesis If the original hypothesis is rejected, a new hypothesis and new experiments are needed If the original hypothesis is accepted, the original hypothesis gains strength and value Further positive testing and evaluation may lead to a hypothesis progressing to the level of a scientific theory Hypothesis are rarely accepted or rejected with absolute certainty! The Scientific Methods: Scientific Theory 47 A hypothesis that has withstood the test of time and evaluation by numerous experiments generally becomes a theory Theories explain the vast amounts of data and observations with a relatively simple set of concepts Theories direct new research and experimentation by raising new questions Theories are never set in concrete and are likely to change over time.  Lecture II 48 Biomolecules and the Central Dogma of Life Learning Objectives 49 49 At the end of this study session, you should be able to: list the four major classes of biomolecules/macromolecules identify the chemical elements that constitute carbohydrates, fats, and proteins understand that large biological molecules are synthesized from smaller units describe how glycosidic, phosphodiester, ester and peptide bonds form compare and contrast DNA and RNA understand the genetic code discuss the flow of genetic information (from DNA to RNA to protein) Biomolecules 50 50 Biomolecules are molecules that occur naturally in living organisms They also include small molecules like primary and secondary metabolites and natural products, that take part in maintenance and metabolic processes These are usually obtained from food  51 Biomolecules 51 Macromolecules monomer monomer monomer  52 Biomolecules 52 All Biomolecules contain CARBON (C) Carbon is the most versatile and prominent element of life Other elements include: HYDROGEN (H) OXYGEN (O) NITROGEN (N) SULPHUR (S) SODIUM (Na) CALCIUM (Ca) MAGNESIUM (Mg) Levels of Organization 53 53 Atoms → Molecules → Macromolecules… Macromolecules are large molecules composed of thousands of covalently connected atoms.  54 Functions of Biomolecules 54 ✓Carbohydrates are the body’s main source of energy. ✓Lipids provide stored energy reserves. This allows us to survive when carbohydrates are not being supplied to the body. ✓Protein helps us stay strong, by forming new bones and muscles, and helping us fight diseases. ✓Nucleic acids are responsible for making each person functional and unique; they are the blueprint for our genetic structure. Making/Breaking of Macromolecules 55 55 Macromolecules are polymers, built from monomers A polymer is a long molecule consisting of many similar building blocks known as monomers Three of the four classes of life’s organic molecules are polymers. These include: - Carbohydrates - Proteins, and - Nucleic acids A dehydration reaction occurs when two monomers bond together through the loss of a water molecule (also called Condensation) Conversely, polymers are disassembled to monomers by hydrolysis, a reaction that is essentially the reverse of the dehydration reaction Making of Macromolecules/Polymers 56 56 Dehydration: Two glucose...can bond molecules together to make (monomers)... maltose (dimer). Breaking of Macromolecules 57 57 Hydrolysis: A dimer such as...can be broken apart maltose, or any into its constituent other polymer... monomers. Polymers 58 58 Macromolecules are made of polymers which are made of smaller, repeating parts called monomers Carbohydrates (polymer) Monosacharrides are the monomers for carbohydrates, joined by glycosidic bond Proteins (polymer) Amino acids are the monomers for proteins (polypeptides), joined by peptide bond Nucleic Acids (polymer) Nucleotides are the monomers for nucleic acids, joined by phosphodiester bond Lipids are not considered polymers. They have no monomers Carbohydrates 59 59 Carbohydrates (polysaccharides) are long chains of sugars. General formula = (CH2O)n Monosaccharides are simple sugars that are composed of 3-7 carbon atoms. They have a free aldehyde (aldoses) or ketone (ketoses) group, which acts as reducing agents and are thus referred to as reducing sugars.  60 Carbohydrates 60 Building Blocks ❑Composed of carbon (C), hydrogen (H), and oxygen (O) in a 1:2:1 ratio Components: ❑Monosaccharides are the monomer ❑Examples C6H12O6 ❑Glucose ❑Galactose ❑Fructose Functions: ❑ Main source of energy for living things (Monosaccharides) ❑ Energy Storage – (polysaccharides) ❑ glycogen in animals ❑ starch in plants ❑ Structural – to build cell walls ❑ cellulose (plants) ❑ chitin (fungi) Carbohydrates 61 61 Oligosaccharide are formed by condensation of 2-9 monosaccharide units. These units are joined with the help of specialized glycosidic linkages. Examples of Oligosaccharides ✓Disaccharides e.g. lactose, maltose, sucrose ✓Trisaccharides e.g. raffinose ✓Tetrasaccharides e.g. stachyose, sesame Lipids 62 62 Lipids are hydrophobic (water fearing) and do not dissolve in water Lipids can be: Saturated: The bonds between all the carbons are single bonds. Solid at room temperature Mainly animal fats Clogs arteries (bad) E.g. stearic acid, palmitic acid, lauric acid, butyric acid Unsaturated: There is at least one double or triple bond between carbons present. Liquid at room temperature Mainly plant-based fats Lowers blood pressure (good) E.g. linolenic acid, linoleic acid, oleic acid, arachidonic acid  Lipids 63 63 Building Blocks: ❑ Mostly made from carbon and hydrogen atoms, some oxygen Components: ❑ A fat molecule consists of 3 fatty acids joined to a molecule of glycerol ❑ Phospholipids in cell membranes are made of a phosphate group and 2 fatty acid chains Functions and Examples: ❑ Long-term Energy storage molecules (fats) ❑ Cell Membranes of organisms (phospholipids) ❑ Steroid Hormone as chemical signals (testosterone/estrogen) Lipids 64 64 Phospholipids – major lipid-related molecule Major component of cell membrane One fatty acid is replaced by a polar phosphate group which creates: a hydrophilic “head” region a hydrophobic “tail” region Proteins 65 65 Proteins are very large molecules made of carbon, hydrogen, oxygen, nitrogen, and sometimes sulfur. Protein molecules are made of smaller molecules called amino acids. Proteins 66 66 Peptide bonds form between amino acids (polypeptide = many peptide bonds = protein) All proteins have a central Carbon atom with 1. carboxylic acid group 2. amino group 3. hydrogen 4. R Group AAs differ in their properties due to differing side chains, called R groups  67 Classes of Amino Acids 67 R-groups determine the properties of individual amino acid.  68 Protein Structure 68 Primary structure: The linear sequence of amino acids linked together by peptide bonds Secondary structure: Polypeptide folding into αn alpha helix or a beta sheet arrangement Tertiary structure: 3-D folding of a single polypeptide chain Quaternary structure: Association of two or more folded polypeptides to form a multimeric protein Nucleic Acids 69 69  Nucleic acids are molecules that store information for cellular growth and reproduction  Elements: C, H, N, O, P  There are two types of nucleic acids: - deoxyribonucleic acid (DNA) and ribonucleic acid (RNA)  These are polymers consisting of long chains of monomers called nucleotides  A nucleotide consists of a nitrogenous base, a pentose sugar and a phosphate group Pentose Sugars 70 70 ❖ There are two related pentose sugars: - RNA contains ribose - DNA contains deoxyribose ❖ The sugars have their carbon atoms numbered with primes to distinguish them from the nitrogen bases Structure of DNA/RNA 71 71 Three Components: Phosphate Group, Pentose Sugar and Nitrogenous base Nitrogenous Bases 72 72 I AGree to Purify a CUTe Pyramid Structure of DNA 73 73 Watson and Crick (1953) determined the three-dimensional structure of DNA by building models. They realized that DNA is a double helix that is made up of a sugar- phosphate backbone on the outside with bases on the inside. Structure of DNA 74 74 Watson and Crick’s discovery built on the work of Rosalind Franklin and Erwin Chargaff. – Franklin’s x-ray images suggested that DNA was a double helix of even width. – Chargaff’s rules stated that A=T and C=G. Structure of DNA 75 75 Erwin Chargaff gave the Chargaff’s rule for the relative estimation of the different nucleotides in the DNA Chargaff’s rule states the amount of adenine in the DNA of a living organism is equal to the amount of thymine in the DNA It also states that the amount of cytosine in the DNA of a living being is equal to the amount of guanine in the DNA Chargaff’s rule: A = T & C = G Also, [A] + [T] + [C] + [G] = 100% Answer this… 76 76 Based on Chargaff's rule for the base composition of double helical DNA, if a sample of DNA contains 24% Thymine (T), what are the percentages of Adenine (A), Cytosine (C), and Guanine (G) in the DNA? Structure of DNA 77 77 Nucleotides always pair in the same way. The base-pairing rules show how nucleotides always pair up in DNA. – A pairs with T – C pairs with G Because a pyrimidine (single ring) pairs with G C a purine (double ring), A T the helix has a uniform width. Structure of DNA 78 78 The sugar-phosphate backbone is connected by covalent bonds. The bases are connected by hydrogen bonds. covalent bond hydrogen bond Formation of Phosphodiester Bonds 79 79 RNA vs DNA 80 80 RNA — Ribonucleic Acid RNA is a messenger that allows the instruction of DNA to be delivered to the rest of the cell RNA is different from DNA in that: 1. The sugar in RNA is ribose; the sugar in DNA is deoxyribose 2. RNA is a single strand of nucleotides; DNA is a double strand of nucleotides 3.RNA is found inside and outside of the nucleus; DNA is found only inside the nucleus 4.Nitrogenous bases in DNA: GCAT 5.Nitrogenous bases in RNA: GCAU  81 Assignment I 81 Describe the contributions of the following scientists to the elucidation of DNA structure and function. - Frederick Griffith - Oswald Avery - Erwin Chargaff - Rosalind Franklin & Maurice Wilkins - Alfred Hershey & Martha Chase - Linus Pauling - James Watson & Francis Crick - Friedrich Miescher  82 The Central Dogma of Life 82 The Central Dogma holds that genetic information is expressed in a specific order, from D N A t o p r o t e i n s y n t h e s i s DNA Replication 83 83 DNA replication is the process of making copies of DNA A single strand of DNA serves as a template for a new strand The rules of base pairing direct replication DNA is replicated during the S (synthesis) stage of the cell cycle Each body cell gets a complete set of identical DNA  84 Models of DNA Replication There are three (3) Models of Replication Semiconservative: each daughter has 1 parental and 1 new strand Conservative: 2 parental strands stay together Dispersive: DNA is fragmented, both new and old DNA coexist in the same strand Semiconservative Replication 85 85 The Process of DNA replication is called ‘semiconservative’ replication. This means that in each new double helix of DNA, one strand was from the parent. Meselson and Stahl Experiments 86 86 Assignment II 87 87 A. Describe the Meselson and Stahl experiments in details. B. What would be the outcome if the experiment continued for: i. three generations ii. four generations iii. five generations DNA Replication Enzymes and Their Functions 88 88 /DNA Gyrase The replication fork 89 89 As the double helix unwinds, the two complementary strands of DNA separate from each other and form a Y shape structure known as the replication fork DNA Replication: leading strand 90 90 RNA primase enzymes begin the replication process by building a small complementary RNA segment called RNA primers (10-60 ribonucleotides long) DNA polymerase III begins to add DNA nucleotides to the primer Since DNA polymerase III only builds in the 5’→3’ direction, the two new strands begin to be assembled in opposite directions DNA polymerase III is able to continue continuously No need for the RNA primase to add additional primers. This is called the leading strand DNA Replication: lagging strand 91 91 On the opposite strand, DNA polymerase III is moving away from the replication fork (lagging strand) RNA primase attaches another primer allowing DNA polymerase III to begin from a new point The pattern created on the second strand is a series of RNA primers and short DNA fragments called Okazaki fragments DNA polymerase I removes the RNA nucleotides and replaces them with DNA nucleotides DNA ligase catalyzes the formations of phosphodiester bonds to seal the strand A General Model for DNA Replication 92 92 1. The DNA molecule is unwound and prepared for synthesis by the action of DNA gyrase, DNA helicase and the single-stranded DNA binding proteins. 2. A free 3'OH group is required for replication but when the two chains separate, no group of that nature exists. RNA primers are synthesized, and the free 3'OH of the primer is used to begin replication. 3. The replication fork moves in one direction, but DNA replication only goes in the 5' to 3' direction. This paradox is resolved by the use of Okazaki fragments. These are short, discontinuous replication products that are produced off the lagging strand. This is in comparison to the continuous strand that is made off the leading strand. 4. The final product does not have RNA stretches in it. These are removed by the 5' to 3' exonuclease activity of Polymerase I. 5. The final product does not have any gaps in the DNA that result from the removal of the RNA primer. These are filled in by the 5’ to 3’ polymerase action of DNA Polymerase I. 6. DNA polymerase does not have the ability to form the final bond. This is done by the enzyme DNA ligase. Checking for Errors 93 93 DNA polymerases that carry out replication also play another important role As they assemble new DNA strands, they proof-read and correct errors (base-pair mismatches) Proof-reading: While creating the complementary strand, if a mismatch occurs, DNA polymerase III may back up, repair, and continue Repairing: DNA repair mechanisms of DNA Polymerase I and II may locate distortions in the strands between replication events and remove a piece of the strand, DNA polymerase III will fill the gap, and DNA ligase will seal the strand Proof-reading 94 94 DNA polymerase III continues adding nucleotides in the forward direction If the enzyme adds a mismatched nucleotide, the enzyme acts as a exonuclease (cleave nucleotides) to remove the mismatched nucleotide The enzyme resumes activity as DNA polymerase Repairing 95 95 DNA polymerase II repairs damage to DNA that occurs between replication events Repair complexes remove several to many bases, leaving a gap in the DNA Gap is filled in by a DNA polymerase, using the template as a guide Nick is sealed by DNA ligase to complete repair Assignment III 96 96 Compare and contrast DNA replication on the leading and lagging strands Transcription: DNA to mRNA 97 97 Transcription is the process by which an RNA sequence is produced from a DNA template There are different types of RNA molecules. Each has a different function in making or synthesizing proteins.  98 Types of RNA 1. Messenger RNA (mRNA) – carries DNAs message from the nucleus to the ribosome.  99 Types of RNA 2.Transfer RNA (tRNA) – carries the correct amino acids to the ribosome so they can be added to the growing protein chain.  100 Types of RNA 3. Ribosomal RNA (rRNA) – makes up part of the ribosome. Helps read mRNAs message and assemble proteins. Transcription Process 101 In the initiation process, the DNA is unzipped by RNA polymerase to expose the template strand RNA polymerase II then begins RNA synthesis at the transcription start point which has the sequence TATAAA (TATA box) Only one of the two DNA strands is copied into an mRNA strand during transcription The strand that gets transcribed is the template or antisense strand The RNA strand is made in the 5→3 direction using the 3→5 DNA strand as template. Transcription Process 102 Nucleotides are added into a complimentary strand of mRNA based on the DNA code. DNA: 3’-ATTCGCACATCAGCT-5’ mRNA: 5’-UAAGCGUGUAGUCGA-3’ The newly formed mRNA moves out of the nucleus to ribosomes in the cytoplasm (for translation) and the DNA re-winds Translation: mRNA to Proteins 103 Translation is the process of protein synthesis in which the genetic information encoded in mRNA is translated into polypeptide chains of amino acids Once the DNA has been transcribed to mRNA, the codons must be translated to the amino acid sequence of the protein The first step in translation is activation of the tRNA Each tRNA has a triplet called an anticodon that complements a codon on mRNA  104 Translation Process Initiation of protein synthesis occurs when an mRNA attaches to a ribosome On the mRNA, the start codon (AUG) binds to a tRNA with methionine The second codon attaches to a tRNA with the next amino acid A peptide bond forms between the adjacent amino acids at the first and second codons The first tRNA detaches from the ribosome and the ribosome shifts to the adjacent codon on the mRNA (this process is called translocation) A third codon can now attach where the second one was before translocation  105 Translation Process Transfer RNA (tRNA) Anticodons on tRNA Codons on mRNA Amino acids are carried by transfer RNA (tRNA) The anticodons on tRNA are complementary to the codons on mRNA  106 Translation Process After a polypeptide with all the amino acids for a protein is synthesized, the ribosome reaches the “stop” codon - UGA, UAA, or UAG There is no tRNA with an anticodon for the “stop” codons Therefore, protein synthesis ends (termination) Finally, the protein is shipped to the Golgi body where it is altered and shipped to where its destination At its final destination, the protein will perform its specific function. Genetic Code 107 The genetic code is the set of rules by which information encoded in mRNA sequences is converted into proteins (amino acid sequences) by living cells It consists of sets of three nucleotides (triplets) in mRNA called codons that specify the amino acids and their sequence in the protein Codons are a triplet of bases which encodes a particular amino acid The codons can translate for 20 amino acids Codons of three bases on mRNA correspond to one amino acid in a polypeptide As there are four bases, there are 64 (43) different codon combinations. Of these, 61 code for the 20 amino acids, 3 code for stop codons Genetic Code 108 Different codons can translate for the same amino acid (e.g. GAU and GAC both translate for Aspartate) therefore the genetic code is said to be degenerate The order of the codons determines the amino acid sequence for a protein The coding region always starts with a START codon (AUG) therefore the first amino acid in all polypeptides is Methionine The coding region of mRNA terminates with a STOP codon (UGA, UAA, or UAG). The STOP codons do not add an amino acid. Instead, it and causes the release of the polypeptide The Genetic Code 109 Features of the Genetic Code 110 The genetic code - is a triplet code - is universal (exceptions exist) - is commaless - is degenerate/redundant - has start and stop signals - nonoverlapping Protein Synthesis 111 1. First transcribe the DNA code into its mRNA. Do this by complimentary base- pairing (A-U, G-C) DNA: 3’-TACGAATTAAGA-5’ mRNA:5’-AUGCUUAAUUCU-3’ 2. Next break the mRNA into codon or three letters. mRNA: AUG CUU AAU UCU  112 Protein Synthesis 3. Plug the codons into the chart and find the amino acids. mRNA: AUG CUU AAU UCU Amino acid: met-leu-asn-ser Peptide bond linkages between amino acids are indicated with red hyphens https://humanbiology.pressbooks.tru.ca/chapter/5-5-genetic-code/ Protein Synthesis 113  114 Haemoglobin mutations Amino Properties Effect on DNA mRNA Disease Acid of AA protein Original Glutamic CTC GAG Hydrophilic Normal None codon 6 Acid Mutation Glutamic CTT GAA Hydrophilic Neutral None 1 Acid Mutation GTC CAG Glutamine Hydrophilic Neutral None 2 Loses Sickle Mutation CAC GUG Valine Hydrophobic water Cell 3 solubility Anaemia 114 Assignment IV 115 For the DNA template: 3′-ATGTTAGGGCTATCCGAT-5’ 1. what would be the sequence of its complimentary strand? 2. what would be the sequence of an mRNA transcribed from it? 3. what would be the anticodons of the complimentary tRNA strands for its mRNA? 4. how many amino acid would be formed from the DNA template? 5. what would be the amino acid sequence formed? Additional Resources 116 YouTube: DNA Replication https://www.youtube.com/watch?v=3jslVQDGkLU Transcription and Translation https://www.youtube.com/watch?v=8wAwLwJAGHs Textbook: Russel, P. J., Hertz, P. E., & McMillan, B. (2017). Biology: The Dynamic Science. (4th ed.). Cengage Learning (Chapters 3, 14 & 15; pages 44-72, 300- 353)  117 It’s just the beginning… Room 203, Faculty of Science Main Building [email protected] +234 (0) 703 556 9436