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Transcript
Cells L2 – Magnification and organelles 17/9/14 Today…. • microscopy, resolution, magnification, EM (photomicrographs), biological drawings, chloroplasts & mitochondria by the end of the day we should be able to… • Work out magnification and size objects • Identify structures within cells from photomicrographs • Deduce cell types/stages from structures within them Size of organelles. The standard measurements: • Metre= 1000milimetres • 1mm= 1000 micrometres (um) • 1um= 1000 nanometres (nm) The size of organelles: Nucleus: 10-20um Chloroplasts: 2-10um in Nucleolus: 1-2um diameter. Rough ER; membranes 4nm thick Ribosomes: 20-25nm Golgi apparatus: variable. Lysosomes: 100nm Mitochondria: 1um wide, up to 10um thick. Centrioles: 0.5umx 0.2um Why do we have many cells? • Complexity (differentiation) • Size • But the basic unit is the same! • or is it?… AS Biology 4 Recognising cells and structures in photomicrographs • Lymphocytes Recognising cells and structures in photomicrographs • Plant leaf Recognising cells and structures in photomicrographs • Cilia on the surface of cells Recognising cells and structures in photomicrographs • Mitochondria Specialised cells - Liver Cell AS Biology 9 Plant cell AS Biology 10 Animal cell Draw the animal and plant cells and surround with information about each organelle AS Biology 11 Organelles • Cells contain organelles – have own membrane. • Specialised tasks. • Most organelles are only visible when the cell is viewed under an electron microscope. • COMPARTMENTALISATION AS Biology 12 Nucleus AS Biology 13 • • • The nucleus Easily seen with light microscope Largest organelle in the cell with a typically spherical shape. The ‘brain’ of the cell. Controls activities within the cell by controlling chemical reactions. (Regulates the synthesis of proteins and enzymes). Within the nucleus is the: • Nucleoplasm: jelly like material, containing chromosomes and 1 or more nucleoli. • The chromosomes contain DNA (deoxyribonucleic acid) attached to proteins called histones. During cell division, the chromosomes within the nucleus become more visible. • A nucleus not under going division can appear grainy because DNA extends throughout the nucleus as chromatin. • Nucleoli: these produce rRNA ( ribonucleic acid) which help to produce ribosomes. Ribosomes produce proteins. Nuclear envelope: • Electron microscope reveals membrane as a double structure. • This separates the nuclear content from the rest of the cell. • Nuclear membrane is continuous with the ER. Space between is very small. • The inner and outer membranes fuse at intervals giving rise to the nuclear pores. AS Biology 14 Nucleus AS Biology 15 Nuclear pores AS Biology 16 Nuclear pores AS Biology 17 Endoplasmic reticulum AS Biology 18 Endoplasmic reticulum AS Biology 19 Endoplasmic reticulum • Made up of a system of parallel cavities or cisternae and membranes. • The ER is continuous with the nuclear envelope. • The fluid filled space between these membranes acts as a transport network for passing materials throughout the cell. • Rough Endoplasmic reticulum • Has ribosomes present on the surface of the membrane which are involved in the synthesis of proteins which are then transported in the rough ER. • The Smooth endoplasmic reticulum • Has no ribosomes and more tubular cisternae than the rough ER.Involved in lipid production and is well developed in cells that produce steroid hormones in the liver. AS Biology 20 Ribosomes AS Biology 21 Golgi apparatus AS Biology 22 Golgi AS Biology 24 Lysosome AS Biology 26 AS Biology 28 Microtubules, cytoskeleton AS Biology 29 Cytoskeleton. Made up of microtubules, microfilaments and intermediate fibres. Microtubules. • Fine, tubular organelles, contribute to complex network of fibrous proteins making up the cytoskeleton, in cytoplasm. • Provide internal skeleton. • Straight, unbranched hollow structures. • Walls made of tubulin (protein) • Increase length by additions of sub units, or shorten by removal, so can be continuously modified. • Components of flagella and cilia AS Biology 30 • Microfilaments: • Solid fibres. • Made of actin (protein) and smaller amounts of myosin. • Both of theses proteins are found in muscle fibres, and interactions between them are the basis of muscle contraction. • Related functions in other cells: e.g. movement of organelles, such as chloroplasts and mitochondria. • Intermediate filament: • Also involved in motility. AS Biology 31 Cillia and flagella • Cilia • Flagella AS Biology 32 Centrioles • Small hollow cylindrical organelles. • In most animal cells and also fungi and some algae. • Walls made up of 9 triplets of microtubules arranged at an angle. • Occur in pairs, arranged at right angles to each other, in AN AREA CALLED the centrosome. • Situated close to Golgi apparatus and appear to have a role in the organisation of the spindle fibres in animal cells. – or do they? RECENT EVIDENCE SAYS NOT • Recent work indicates they may be the site of the formation of the whole cytoskeleton network. AS Biology 33 cilia AS Biology 34 Cilia and flagella microtubule arrangement 9+2 AS Biology 35 Movement of cilia and flagella AS Biology 36 Microvilli • Minute finger shaped outgrowths/ folds of plasma membrane e.g animal cells: epithelium lining of small intestine. • Plant cells have cell wall, which prevents such projections. • Function, to increase surface area of cells, allowing for increased absorption of materials. • Contain many microfilaments of proteins actin and myosin. These probably maintain the shape of microvilli but also involved in moving them from side to side. AS Biology 37 L2 part 2 - Chloroplasts and mitochondria mitochondria AS Biology 39 PURPOSE - mitochondria • The cells main source of power • Provide eukaryotic cells with energy • Main function is to help with the respiration process STRUCTURE • The mitochondria is normally rod shaped but can be found as a circle. • The mitochondria is surrounded by a double membrane • There is a space between these two membranes • The inner membrane has folds which are called CRISTAE. These are surrounded by the MATRIX – a jelly-like substance which contains mitochondrial DNA and RIBOSOMES. Internal structure • Mitochondrial inner membrane has little stalks with spheres on the end = ‘elementary particles’ • The ATP producing enzyme is located in the stalks. KREBS/CITRIC ACID CYCLE • This cycle is used to get as many electrons out of the food we eat as possible • The electrons are then used to produce ATP which is then used for all kinds of cellular functions such as movement, transport, entry and exit of products etc. What happens – in brief • Glucose split to 2 pyruvate molecules in cytosol = glycolysis. • In mitochondria breakdown of glucose is completed in citric acid cycle and CO2 formed • At each stage electrons are produced and stored in mitochondria in a way they can be used to make ATP DIAGRAM OF MITOCHONDRIA • Draw mitochondrion and note how it actually looks from page 16 Mitochondria • Mitochondria – present in higher, complex cells and are the site of aerobic respiration.The matrix contains enzymes involved in the tricarboxylic acid (TCA) cycle/ Krebs cycle. • Adenosine triphosphate (ATP) – reactions in which the ‘energy currency’ of the cell is produced, takes place at the cristae. • Membrane structure –Double membrane. Two phospholipid membranes, the outer is smooth and the highly folded inner membranes.( cristae) • The cristae – formed from the highly folded inner membrane which gives a large surface area. These structures contain enzymes for the final stages of respiration. • Matrix – contains enzymes which catalyse reactions in early stages of respiration.Also mitochondrial ribosomes, which are smaller than those found in the cytoplasm of the cell, and mitochondrial DNA, as a AS Biology 46 circular strand. mitochondria AS Biology 47 Chloroplasts • Chloroplasts occur in the cells of the photosynthetic tissue of plants. • They belong to a group of organelles known as plastids, which often contain pigments. • Chloroplasts occur in large numbers in the palisade cells of the leaves of flowering plants. Structure of chloroplasts • They are disc-shaped structures and appear green due to the presence of the pigment chlorophyll. • They range from 2 to 5 micrometres in diameter and are 1 micrometre thick, easily seen using a light microscope. • Electron microscopy shows that each chloroplast is surrounded by a double membrane, the chloroplast envelope, enclosing the stroma in which there is a system of flattened membranous sacs called thylakoids/lamellae. • Grana are formed from several thylakoids, or lamellae, stacked together in the matrix. Grana: Inside a plant cell’s chloroplasts are tiny grana. Each granum contains chlorophyll, which absorbs light rays. Thylakoids/Lamellae: These are sheet like membranes, whose function is to hold the chlorophyll molecules in a suitable position for trapping the maximum amount of sunlight. Stroma: The lamellae are embedded in a watery medium called the stroma. This contains the enzymes needed for photosynthesis. The building of carbohydrates also takes place in the stroma. Chloroplast from leaf palisade cell, showing internal structure Electronmicrograph of chloroplast The site where photosynthesis takes place. The lightdependant reaction of photosynthesis happens in the grana, and the lightindependent reaction of photosynthesis happens in the stroma. STRUCTURE OF THE CHLOROPLAST The structure of the chloroplast is bounded by a double membrane within which are numerous structures called thylakoids. Each thylakoid consists of a pair of membranes close to each other with a narrow space between. In places the thylakoids are arranged in neat stacks, rather like a pile of coins. • • • • question 1 The organelles attached to the surface of rough endoplasmic reticulum are: centrioles, cisternae, lysosomes, ribosomes question 2 Small cylindrical structures containing microtubules and found near the nucleus are called: centrioles, cisternae, lysosomes, ribosomes • question 3 In electron micrographs, a transverse section of a cilium or flagellum shows an arrangement of: 9 outer and 1 central microtubules, 9 outer and 2 central microtubules 11 outer and 2 central microtubules, 11 outer and 4 central microtubules • question 4 All of the following organelles are only visible using an electron microscope except: centrioles, microtubules, mitochondria, ribosomes • • • • • question 5 All of the following are membrane-bound organelles except: chloroplasts, lysosomes, mitochondria, ribosomes question 6 All of the following are organelles except: cell wall, chloroplasts, mitochondria, ribosomes What is the function of the golgi? What are the internal folds of mitochondria called? Where would RNA go once it leaves the nucleus? What are microtubules made of? Where is energy produced in the cell? What are the two types of ER? What might happen to old organelles in the cell? Via which organelle does modified protein get transported out of the cell? How do you work out overall magnification? H/W • What are your e.mail addresses? • Mine is… [email protected] • Read chapter 1 and answer the book questions • Draw up a table about similarities and differences of chloroplasts and mitochondria (e.g. energy production, membrane bound, contain DNA…)