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Note On Eukaryotic Cells

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Published in: Biology
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Eukaryotic Cells

Areesha A / Dubai

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Qualification: IGCSE-AS Level-A level

Teaches: Biology, Chemistry, English, Physics, Science, Phonics, Maths, English Language

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  1. 2.4 Eukaryotic Cells Lesson Objectives: Learners should be able to demonstrate and a I their knowledge and understanding of: The ultrastructure of eukaryotic cells and the functions of the different cellular components Photomicrographs of cellular components in a range of eukaryotic cells The importance of the cytoskeleton
  2. (a) Bell Task • Label the diagram of the animal cell • Which features can you identify from GCSE • Use the textbook to help
  3. OCR ASTeacherSupport co (a) ist the functions of the organelles you have studied at GCSE • Nucleus • Mitochondria Ribosomes • Cell Membrane • C toplasm Week 2 (j
  4. microtubule network nucleolus nucleus Golgi apparatus A Figure 3 A drawing of a eukaryotic animal cell showing the many other components that are not visible with a light microscope cell-surface membrane cytosol ribosome centriole rough endoplasmic reticulum smooth endoplasmic reticulurn cytoskeleton secretory vesicles mitochondria
  5. What is a eukaryote? A eukaryote is any organism consisting of one or more cells that contain DNA in a membrane-bound nucleus, separate from the cytoplasm. Eukaryotes include: • animals plants • fungi • a diverse group known as the protists (or protoctists). board works All eukaryotic cells contain a large number of specialized, membrane-bound organelles. 5 of 37 Boardworks Ltd 2008
  6. ribosome glucose molecule double helix protein Relative Sizes red blood width of human hair water 0.1 nm mintmum resolvable by electron microscope A Figure 1 10 100 nm cell bacterium 1000 nrn (l pm) mrnmum resolvable by light microscope 100 gm tennis ball 10 mm 100 mm IOOOgrn (1 mm) mjrnmum resolvable by unaided 1000 mm This diagram illustrates the relative sizes of the different components of living organisms
  7. The Nucleus Chromatin Nucleolus Nuclear Envelope
  8. Nucleus — Structure & Function Nucleus — houses nearly all the cell's genetic material Chromatin — consists of DNA and proteins Nucleolus — makes RNA, which is made into ribosomes and ribosomes Nuclear envelope — has nuclear pores going through the envelope to let relatively large molecules pass through. In the nuclear envelope there is nucleoplasm. Nuclear envelope Nucleus Nucleolus Rough endoplasmic reticulum Ribosome
  9. Nucleus — The Facts The largest organelle in the cell Consists chromatin which contains DNA and proteins Chromatin is seen as darkened patches when seen on a light micrograph • Some of these proteins regulate the cell's activity Makes ribosomes • Has holes called nuclear pores which allow exchange of substances in and out of the cell
  10. Nucleolus — The Facts • The most obvious structure in the nucleus is the nucleolus • The nucleolus produces ribosomes, which move out of the nucleus to latch onto the outside of the rough endoplasmic reticulum where they produce proteins The* us
  11. Nuclear envelope • It is a dense spherical structure Surrounds the nucleolus A structure made of two membranes (inner and outer) with fluid separating them The nuclear envelope is marked with nuclear pores which allow for exchange of relatively large molecules Outer Perinuclear Space Inner Membrane Nuclear Pore Complex Nuclear Envelope Anatomy Figure 1
  12. Mitochondria board works The mitochondrion is an energy-generating organelle. It is surrounded by two membranes. The inner layer folds inwards to form the cristae. The cristae project into a liquid called the matrix. outer membrane matrix cristae inner membrane The inner membrane is coated in enzymes, which catalyze the reactions of aerobic respiration to produce ATP. 120f37 Boardworks Ltd 2008
  13. OCR ASTeacherSupport co Mitochondrion 2-5 m Ion Cristae Matrix Outer membrane Inner membrane Please note that magnification sizes are subject to variation on dfferent screens Intermembrane space Week 2 Look at the diagram of the mitochondria. What is the function of the mitochondria? • How does the function of the mitochondria relate to this function? The Mitochondria contains is one DNA Suggest why the Mitochondria has its own DNA? Ltd 2c.as have the
  14. Ribosomes They are tiny organelles which can be found in cytoplasm or bound to rough endoplasmic reticulum. Each ribosome consists of two sub-units. They are the site of protein synthesis in a cell, which is where proteins are made. It acts as an assembly line for coded information form the nucleus to be used to make proteins from amino acids. Membrane Figure I Ribosomes
  15. GolgiApparqtus 00 transport ve•cle The Golgi Apparatus is a stack of membrane- bound flattened sacs. • Its single membrane is similar to that of a cell membrane in that it has two layers. • Its membrane surrounds an area of fluid where the complex molecules are stored and changed.
  16. Golgi Apparatus - Function Golgi Apparatus receives proteins from the ER and modifies them. • It may add sugar molecules to them. The Golgi apparatus then packages the modified proteins into vesicles that can be transported. Some modified proteins may go to the surface of the cell so that they may be secreted. Vesicles bringing materials to and from the Golgi apparatus
  17. Lysosomes They are spherical sacs surrounded by a single membrane. They are specialised vesicles They contain powerful digestive enzymes and their role is to break down materials. Goo
  18. Endoplasmic Reticulum Rough Endoplasmic Smooth Endoplasmic Reticulum Reticulum • Consists of a series if They have the same flattened membrane — structure as a rough bounds sacs called endoplasmic reticulum but cisternae. it does not have ribosomes. They are studded with ribosomes. It is involved in making the lipids that the cell needs • It transports proteins that were made on the attached ribosomes. En do asmic Figure I • Some of the proteins will be secreted by the cell whilst N u Clear the others will be placed on the surface of the cell membrane. Endo la smic
  19. Centrioles Centrioles are self-replicating organelles made up of nine bundles of microtubules and are found only in animal cells. They help in organizing cell division, but aren't always needed in the process. Centriole Structure Centriole Pair Microtubule Triplet Figure 1
  20. Cilia and Flagella • For single-celled eukaryotes, cilia and flagella are essential for the locomotion of individual organisms. In multicellular organisms, cilia function to move fluid or materials past an immobile cell as well as moving a cell or group of cells. When microtubule pairs try to slide past each other, the axoneme bends because the microtubules are anchored at the base. Dynein 'arms' Undulipodium Axoneme Base of undulipodium The motor protein, dynein, has •arms' that can push one doublet ahead of the other
  21. The Nucleus Nucleus Nucleolus Rough endoplasmic reticulum Ribosome - Function Nuclear envelope Structure The nucleus is the largest organelle. When stained, it shows darkened patches known as chromatin. It is surrounded by a nuclear envelope. This is a structure made of buo membranes with fluid between them. A lot of holes, called nuclear pores, go right through the envelope. These holes are large enough for relatively large molecules to pass through. There is a dense, spherical structure, called the nucleolus, inside the nucleus. The nucleus houses nearly all the cell's genetic material. The chromatin consists of DNA and proteins. It has the instructions for making proteins. Some of these proteins regulate the cell's activities. When cells divide, chromatin condenses into visible chromosomes (see spread 1 , 1.14). The nucleolus makes RNA and ribosomes. These pass into the cytoplasm and proteins are assembled at them.
  22. Mitochondria Inner crista outer membrane Note: matrix Mitochondria Cristae Matrix A Figure S Electron micrograph and can be drawing ofa mitochondrion x30000 shown as magnification Structure round Outer membrane Inner membrane Function Intermembrane space These may be spherical or sausage-shaped. They have two membranes separated by a fluid-filled space. The inner membrane is highly folded to form cristae. The central part of the mitochondrion is called the matrix, Mitochondria are the site where adenosine triphosphate (ATP) is produced during respiration, ATP is sometimes called the universal energy carrier because almost all activities that need energy in the cell are driven by the energy released from ATP.
  23. Structure Golgi Apparatus A Figure 9 Transmission electron micrograph of the Golgi apparatus. Golgi are membrane-bound organelles thor modify and package proteinsfor onward transport. x 8000 magnification Function Vesicles bringing materials to and from the Golgi apparatus A stack of membrane-bound, flattened sacs, (It looks a bit like a pile of pitta bread.) Golgi apparatus receives proteins from the ER and modifies them. It may add sugar molecules to them, The Golgi apparatus then packages the modified proteins into vesicles that can be transported. Some modified proteins may go to the surface of the cell so that they may be secreted
  24. Endoplasmic Reticulum Structure ER consists of a series of flattened, membrane-bound sacs called cisternae. They are continuous with the outer nuclear membrane. Rough endoplasmic retjcu/um is studded with ribosomes. Smooth endoplasmic retjculum does not have ribosomes. Function Rough ER transports proteins that were made on the attached ribosomes, Some of these proteins may be secreted from the cell. Some will be placed on the cell surface membrane. Smooth ER is involved in making the lipids that the cell needs. A Figure ? Coloured TEM showing the rough endoplasmic reticulum (folds, centre). The cell nucleus is partially seen to the left. The round structures are vesicles that are being used to transport proteins from the rough endoplasmic reticulum to elsewhere in the cell. Magnification x 20000
  25. Lysosomes Structure These are spherical sacs surrounded by a single membrane. Function Lysosomes contain powerful digestive enzymes. Their role is to break down materials. For example, white blood cell lysosomes help to break down invading microorganisms; the specialised lysosome (acrosome) in the head of a sperm cell helps it penetrate the egg by breaking down the material surrounding the egg.
  26. Organelles without membranes Ribosomes Structure These are tiny organelles. Some are in cytoplasm and some are bound to ER. Each ribosome consists of two subunits. Centrioles Structure These are small tubes of protein fibres (microtubules). There is a pair of them next to the nucleus in animal cells and in the cells of some protoctists. Function Ribosomes are the site of protein synthesis in the cell (where new proteins are made). They act as an assembly line where coded information (mRNA) from the nucleus is used to assemble proteins from amino acids. Function Centrioles take part in cell division. They form fibres, known as the spindle, which move chromosomes during nuclear division (see spread 1.1.4).
  27. Review Questions Summary questions Answer the exam questions on the sheet 1 2 3 4 S 6 What is a lysosome and why is the membrane that surrounds (3 marks) it so important? Explain why cells need to be compartmentalised, and describe three (4 marks) examples of compartmentalisation within an animal cell. Compare the structure and function of the rough and smooth endoplasmic reticulum. Describe the structure and function of the cytoskeleton. Given the following information about a eukaryotic cell (3 marks) (5 marks) ? x 10? base pairs of DNA per chromosome 0.34 x 10-9 m per base pair diploid number is 46 a Calculate the length of DNA in a single cell. Give your answer in metres. b Suggest how this DNA is packed into a cell only 50 pm in diameter. Discuss how the structure of microfilaments and microtubules means these components of the cytoskeleton are involved in the movement of (6 marks) cells but the intermediate fibres are not.

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