1_cell_structure.pdf

1 Cell structure 1.1 The microscope in cell studies ANIMAL CELL a) Differences between plant and animal cells PLANT CELL Images: Cambridge International AS & A Level Bi...

1 Cell structure 1.1 The microscope in cell studies ANIMAL CELL a) Differences between plant and animal cells PLANT CELL Images: Cambridge International AS & A Level Biology Coursebook b, c, e) Magnification calculations LIGHT MICROSCOPE ANIMAL CELL CONVERSIONS 1 mm = 1000 or 103 µm 1 µm = 1000 or 103 nm PLANT CELL d) Resolution and magnification Ø magnification – how much bigger a sample appears to be under a microscope than it is in real life ELECTRON MICROSCOPE Ø resolution – the ability to distinguish between 2 separate points. - as resolution increases, image clarity and detail also increase Types of microscopes LIGHT ELECTRON SEM – 3 nm RESOLUTION 200 nm TEM – 0.5 nm MAGNIFICATION x1500 x250,000 – x500,000 1 www.alevel-notes.weebly.com a) Light microscopes a) Electron micrographs of plant and animal limit of resolution: half the wavelength cells ribosomes (25nm) can’t be seen with a light a) Plant cells microscope as they don’t interfere with the light waves Image: https://cronodon.com/BioTech/Plant_Bodies_Cells.html Image: Cambridge International AS & A Level Biology Coursebook different stains are absorbed by different cell organelles so they can be observed more clearly b) Electron microscopes vacuum (electrons cannot be focused without a vacuum as they will collide with air molecules and scatter) water boils at room temperature in a vacuum, so the sample must be dehydrated (specimen has to be Image: https://www.tuttee.co/blog/gce-cie-biology-animal-and-plant-cell-structures-and-functions dead) Advantages of a light microscope over an electron microscope b) Animal cells 1) can observe living tissue 2) more portable 3) easier to use - no technical training required 4) possible to see real/natural colours and a live specimen 5) can stain particular types of tissue for better visibility 1.2 Cells as the basic units of living organisms The cell is the basic unit of all living organisms. The interrelationships between these cell structures show Image: https://brainly.in/question/1540878 how cells function to transfer energy, produce biological molecules including proteins and exchange substances with their surroundings. 2 www.alevel-notes.weebly.com  carry out protein synthesis 80S – cytoplasm 70S – chloroplasts & mitochondria 4) Rough endoplasmic reticulum (RER) membranes that form an extended system of fluid- filled sacs (cisternae) single membraned organelle ribosomes are attached to the RER and are the site Image: https://www.tuttee.co/blog/gce-cie-biology-animal-and-plant-cell-structures-and-functions of protein synthesis proteins made by the ribosomes enter the sacs and b) Eukaryotic cell structures and their functions are often modified as they go through them small sacs (vesicles) break off from the ER and join 1) Cell surface membrane (phospholipid bilayer) to form the golgi body (7 nm) selectively permeable membrane that allows for the exchange of certain substances barrier between cytoplasm and external environment cell recognition (surface antigens) selection of substances that enter/leave cells 2) Nucleus (7 µm) Controls cell’s activities very dense, takes up colour the most when stained divides first during cell division surrounded by 2 membranes, known as the nuclear envelope which is continuous with the RER. Image: Esrefoglu, Mukaddes. (2019). The Golgi Apparatus: Morphology and Function with Recent Facts. Bezmialem Science. 7. 331-338. 10.14235/bas.galenos.2019.2806. 5) Golgi body / apparatus / complex Image: https://courses.lumenlearning.com/boundless-ap/chapter/the-nucleus-and-ribosomes/ contains: a) nuclear pores: allow and control substances entering in (protein to make ribosomes, ATP, some hormones, nucleotides) and leaving (mRNA, ribosomes for protein synthesis) of nucleus Image: https://microbenotes.com/golgi-apparatus-structure-and-functions/ b) nucleolus (2.5 µm): contains loops DNA from stack of flattened sacs (cisternae) formed by the several chromosomes and synthesises ribisomes vesicles which bud off from the RER Single membraned organelle 3) Ribosomes (25 nm) Packages substances into vesicles for transport composed of 2 subunits glycosylation phosphorylating proteins assembly of polypeptides into proteins (4º structure) folding proteins removing the 1st amino acid methionine to activate Image: https://www.open.edu/openlearn/ proteins 3 www.alevel-notes.weebly.com  energy released from energy-rich molecules e.g., 6) Smooth endoplasmic reticulum (SER) sugars and fats during respiration is transferred to molecules of ATP synthesizes lipids and steroids such as cholesterol ATP is the energy-carrying molecule in all living cells and the reproductive hormones estrogen and testosterone. once made, ATP leaves the mitochondrion and can spread rapidly to all parts of the cell where energy is needed its energy is released by breaking ATP down to ADP (adenosine diphosphate) in a hydrolysis reaction see Chapter 12.2(i) for more details 9) Microtubules Image: https://studiousguy.com/ 7) Lysosomes (0.1-1µm) spherical sacs surrounded by a single membrane not permanent structures no internal structure contain hydrolytic enzymes Image: https://www.microscopemaster.com/alpha-and-beta-tubulins.html responsible for digestion/breakdown of unwanted long, rigid, hollow tubes found in the cytoplasm structures e.g., old organelles made of a protein called tubulin can even digest whole cells e.g., in mammary glands after the period of lactation tubulin has 2 forms – ⍺ & β tubulin ⍺ & β tubulin molecules combine to form dimers many dimers are joined end to end to form protofilaments 13 protofilaments are in a ring to form a cylinder with a hollow center this cylinder is the microtubule Image: https://www.ybstudy.com/2020/07/lysosomes-structure-functions.html?m=1 supports and gives shapes to the cell 8) Mitochondria (0.5-10µm) the assembly of microtubules from tubulin molecules is controlled by special locations in cells called microtubule organizing centers (MTOCs) 9.5) Centrioles (and centrosomes) outside the nucleus of animal cells, 2 centrioles are present close together at right angles in a region called the centrosome Image: https://brainly.in/question/21632838 carries out aerobic respiration synthesizes ATP (adenosine triphosphate) more in cells that have a higher demand for energy e.g., muscle, liver, and root hair cells outer membrane contains a transport protein called porin Image: https://www.microscopemaster.com/centriole.html 4 www.alevel-notes.weebly.com  13) Vacuoles centrioles are hollow cylinders about 500 nm long surrounded by a partially permeable tonoplast which produces spindle fibers controls exchange between the vacuole and organizes microtubules cytoplasm 10) Chloroplasts (3-10µm) helps regulate osmotic properties of cells fluid present in the vacuole consists of: Image: https://askmicrobiology.com/do-bacteria-have-chloroplast/ diameter 3-10 um carries out photosynthesis contains starch grains, circular DNA, and 70S ribosomes ATP is also produced here see Chapter 13.3(a) for more details d) Structural features of prokaryotic cells organisms that lack nuclei or proper nuclear 11) Cell wall membranes are called prokaryotes gives cell definite shape unicellular rigid as made of cellulose 1-5um freely permeable cell wall made of murein (peptidoglycan = protein + prevents cell from bursting polysaccharides) no membranes around organelles 12) Plasmodesmata 70S (smaller) ribosomes plant cells are linked to neighboring cells by means of genetic material in the form of circular DNA fine strands of cytoplasm called plasmodesmata have no ER which pass through pore-like structures in their walls Image: https://mybody101.com/ap-bio-unit-4/ allows the transport of water, sucrose, amino acids, ions, etc., between cells without crossing membranes this is called movement through the symplastic pathway allows communication/signaling between cells. Image: Cambridge International AS & A Level Biology Coursebook 5 www.alevel-notes.weebly.com e) Differences between typical eukaryotic and prokaryotic cells Image: https://www.researchgate.net/fi See Chapter 18.2 for more details f) Viruses Image: Cambridge International AS & A Level Biology Coursebook noncellular/acellular protein coat nucleic acid core; DNA/RNA strand replicate inside host cells only show no characteristics of living organism symmetrical shape the virus DNA/RNA takes over the protein synthesizing machinery of the host cell which helps to make new virus particles See Chapter 18.2(d) for more details 6 www.alevel-notes.weebly.com