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 BIOL1003 Human Biology Exam Notes Date: Friday 20 June 2014 Weight: 50% Length: two hours, 75 multiple choice questions The Microscope •
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Operate the compound light microscope and the dissecting microscope to examine specimens. Apply a scale to your drawings. Estimate the size of microscopic objects. Cell Structure Describe the structures and functions of a cell. • Emergent Properties: Atoms •
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Molecules Cells Tissues Organs Systems Organism Four major tissue types: o Epithelial o Connective o Muscle o Nervous The Cell Theory o All living things are composed of cells (or cell products). o The cell is the smallest unit of life. o Cells only arise from pre-­‐existing cells. All cells originate as basic neutral cells (stem cells) but differentiation/specialisation of the cell occurs so that it can exhibit a particular function. Function of eukaryotic organelles: compartmentalise chemical reactions. Types of organelles: o Nucleus: contains hereditary material (DNA), controls cell activities and mitosis. o Nucleolus: ribosome synthesis. o Ribosome: polypeptide synthesis. o Rough Endoplasmic Reticulum: studded with ribosomes and involved in the synthesis and transport of proteins destined for secretion. o Smooth Endoplasmic Reticulum: involved in the synthesis and transport of lipids and steroids, as well as metabolism of carbohydrates. o Cytoplasm: every part of the cell that is within the cell membrane excluding the nucleus and its sub-­‐parts. o Cytosol: the fluid in which all the other organelles float. o Cytoskeletal system: backbone of the cell. ! Types of cytoskeletal filaments: • Microtubules – centrioles, cilia (important for locomotion in bacteria) and flagella (important for movement in sperm). • Intermediate filaments – mechanical support for cells, actin, myosin, make up the shape of the cell. 2 Microfilaments – microvilli (important for increasing surface area). o Centrioles: allow mitosis to occur by extending microfilaments (spindle fibres). o Mitochondria: cellular respiration, has it’s own DNA (endosymbiosis theory), provides the cell with energy in the form of ATP. o Vesicle: contains material produced in the cell; formed by the Golgi and secreted by exocytosis. o Lysosome: breakdown of macromolecules, site of hydrolysis, digestion. o Golgi apparatus: process and package proteins (carbohydrates, lipids, hormones, channel proteins). o Plasma membrane ! Semi-­‐permeable barrier that controls the entry and exit of substances. ! Phospholipid membrane allows fluidity of membrane. ! Hydrophilic phosphate head and two hydrophobic fatty acid tails connected by glycerol. • Functions of the cell: o Cell metabolism and energy use: ! Cell metabolism: the collective chemical reactions that occur within cells. ! Energy released during metabolism is used for cell activities (e.g. new molecules synthesis, muscle contraction, heat production). o Synthesis of molecules: ! Cells synthesise various types of molecules (proteins, nucleic acids, lipid). ! The different cells of the body do not all produce the same molecules. ! The structural and functional characteristics of cells are determined by the types of molecules they produce. o Communication: ! Cells produce and receive chemical and electrical signals that allow them to communicate with one another (e.g. nerve cells). o Reproduction and inheritance: ! Each cell contains a copy of the genetic information of the organism. ! Specialised cells (sperm cells and oocytes) transmit that genetic information to the next generation. Explain surface area to volume ratios in relation to cells. !"##
• The rate of metabolism of a cell is a function of its !"#$%&. •
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The rate of material exchange in and out of a cell is a function of its surface area. As the cell grows, volume increases faster than surface area (leading to a decreased SA:Vol ratio). 3 •
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If the metabolic rate is greater than the rate of exchange of vital materials and wastes, the cell will eventually die. Hence the cell must consequently divide in order to restore a viable SA:Vol ratio and survive. Cells and tissues specialised for gas or material exchange (e.g. alveoli) will increase their surface area, without changing volume, to optimise the transfer of materials. Describe the structure of DNA and how it replicates. Structure •
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A nucleotide, the basic unit of DNA, is a molecular structure consisting of a phosphate group, a pentose sugar (deoxyribose) and a nitrogenous base. o Nitrogenous bases: ! Purines (double ring): adenine, guanine ! Pyrimidines (single ring): thymine, cytosine. How nucleotides attach to other nucleotides to form a strand: o Nucleotides are linked into a single strand via a condensation reaction. o The phosphate group (attached to the 5'-­‐C of the sugar) joins with the hydroxyl (OH) group attached to the 3'-­‐C of the sugar. o This results in a phosphodiester bond (type of covalent bond) between the two nucleotides and the formation of a water molecule. The Double Helix Structure o Two polynucleotide chains of DNA are held together by hydrogen bonds between complementary base pairs. ! Adenine pairs with thymine (A=T) via two hydrogen bonds. ! Guanine pairs with cytosine (G=C) via three hydrogen bonds. o In order for bases to be facing each other and thus able to pair, the two strands must run in opposite directions (i.e. they are anti-­‐parallel). ! Leading strand (5’ to 3’ direction) vs. lagging strand (3’ to 5’ direction). ! Lagging strand: DNA synthesis begins at the fork and so soon runs out of template – discontinuous -­‐ Okazki fragments. o As the polynucleotide chain lengthens, the atoms that make up the molecule will arrange themselves in an optimal energy configuration. o This position of least resistance results in the double-­‐stranded DNA twisting to form a double helix with approximately 10 -­‐ 15 bases per twist. Replication •
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DNA replication occurs in the nucleus. Steps involved: 4 Helicase: Unwinds the DNA and separates the two polynucleotide strands by breaking the hydrogen bonds between complementary base pairs. The two separated polynucleotide strands act as templates for the synthesis of new polynucleotide strands. ! DNA Polymerase: Synthesises new strands from the two parental template strands using free deoxyribose nucleotides by aligning them opposite their complementary base partner and covalently bonding them together to form a complementary nucleotide chain. Complementary Base Pairing Rule: o Each of the nitrogenous bases can only pair with its complementary partner (A=T ; G=C). o When DNA is replicated: ! The new strands formed will be identical to the original strands separated from the template. ! The two DNA molecules formed will be identical to the original molecule. Semi-­‐Conservatism: o DNA replication is a semi-­‐conservative process because a new double-­‐
stranded DNA molecule has one strand from the original molecule and one which was newly synthesised. !
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Describe the stages of the cell cycle. • Mitosis: a process during cell division in which the cell nucleus divides into two. • Cytokinesis: the division of the cell’s cytoplasm following the division of the nucleus. • Interphase o The stage in the development of the cell between two successive M phases (90% of cell cycle). o Stages ! Growth 1 (G1): cell grows and matures. ! Synthesis (S): copies DNA. ! Growth 2 (G2): prepares for division. o Sometimes cells will leave the cell cycle and enter into a quiescent state (G0), whereby it becomes amitotic and no longer divides. • M phase o Mitosis ! Prophase: Chromosomes become viable as long thin threads. DNA twists and curls forming thicker and shorter supercoils to become two chromatids joined at the centromere. Nuclear membrane disappears and a spindle forms. 5 Metaphase: Chromatids line up at the equator of the cell and centre of spindle. Centromere is attached to spindle microtubules. Supercoiling is at maximum. ! Anaphase: Centromere splits. Spindle fibres shorten pulling the two chromatids apart taking each to opposite poles. ! Telophase: Chromosomes at each pole and nuclear membrane forms around each cluster. Spindle fibres disappear. At the end of telophase cytokinesis occurs and two smaller daughter cells are formed. o Cytokinesis: the division of the cytoplasm into two. !
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