Structures in Cells. Cytoplasm. Lecture 5, EH1008: Biology for Public Health, Biomolecules

Transcription

1 Structures in Cells Lecture 5, EH1008: Biology for Public Health, Biomolecules 1 Cytoplasm Nucleus Centrioles Cytoskeleton Cilia Microvilli 2 Cytoplasm Cellular material outside nucleus but inside plasma membrane Composed of cytosol, cytoskeleton, cytoplasmicinclusions, Organelles Cytosol:fluid portion. Dissolved molecules (ions, sugars, amino acids, etc. in water) and colloid (proteins in water). Organelles can not move about freely Cell contents arecompartmentalised specialisedregions for particular functions 3

2 Nucleus Most prominent organelle membrane bound Visible with light microscope All body cells have one at some stage of life cycle 10 mm Red blood cells loose them as they develop Skeletal muscle, trophoblasts of placenta & osteoclasts of bone more than one. 4 Bound by double bilayer nuclear envelope Nuclear envelope contains nuclear pores Nuclear pores- regulates the trafficking of ions, proteins & RNA. Contains genetic information DNA- Chromosomes - Chromatin Often has a dense region known as the nucleolus lacks membrane -RNA 5 Nucleus contains clumps of darker material- heterochromatin 6

3 Chromosome Structure Chromatin: DNA complexedwith proteins (histones) During cell division, chromatin condenses into pairs of chromatids called chromosomes. Each pair ofchromatidsis joined by a centromere 7 Cytoskeleton Supports the cell but has to allow for movements like changes in cell shape and movements of cilia Intracellular motility Cell locomotion Cell Shape 1. Microtubules 2. Microfilaments 3. Intermediate filaments 8 Frame work that underlies organisation in the cell Cytoskeleton: meshwork of protein fibres Provides structural support, also allows cellular movement Microfilaments: actin, solid, twisted double chain, just inside cell membrane - shape of the cell s surface and whole cell locomotion Intermediate filaments: fibrous proteins, rope-like structure, reinforce cell shape, mechanical strength. Microtubules:straight, hollow, tubulins, scaffolding within cells to maintain shape, intracellular transport, allow organelle movement 9

4 Microtubules Microtubules are the largest-diameter cytoskeleton components nm in diameter. Microtubules can be very long Hollow cylinders Composed of protein tubulin Involved in a wide array of essential cellular activities: i. Cell elongation and movement ii. Maintenance of cell shape and support iii. Beating of cilia and flagella 10 Play an important role in organising the spatial distribution of organelles within cells. Microtubules serve as tracks along which organelles can move Intracellular transport of secretory granules Movement of chromosomes during meiosis & mitosis 11 Centrioles and Spindle Fibers Located incentrosome: specialized zone near nucleus. Contain 2 centrioles Center of microtubule formation Microtubules role in determining cell shape 12

5 Centrioles Before cell division, centriolesdivide, move to ends of cell and organize spindle fibers 13 Cilia Cylindrical appendages projecting from cell surfaces 10 µm length Cells line the respiratory tract, female reproductive tract Consists of 2 centrally located microtubules and 9 peripheral pairs 14 Capable of movement Moves materials over the cell surface 15

6 Flagella Similar to cilia but longer Usually only one per cell Move the cell itself in wave-like fashion Example: sperm cell 16 Microfilaments Microfilaments consist of two twisted-together chains of actinprotein subunits Microfilaments are the smallest in diameter of the cytoskeleton components- 5nm Important for cell shape Together with the protein myosin, microfilaments make up the contractile organelles within muscle cells ATP powers movement of actin filaments relative to myosin Actin and myosin is involved in the dividing of cytoplasm (pinching together of plasma membrane) during cell division Involved in projection of pseudopodia Support microvilli (non-movable finger-like projections) 17 Microvilli Extension of plasma membrane - 1µm Normally many on each cell Do not move supported by actin filaments Increase the cell surface area Found on cells of kidneys, intestines- absorption 18

7 Intermediate filaments Stable fibrous structure made up of different irregular molecular strands specific to cell type Intermediate filaments have a diameter that is intermediate between that of microtubules (smaller) and microfilaments (bigger) nm More permanently assembled than microtubules or microfilaments Mechanical strength Serve to reinforce the shape of a cell as well as anchor various organelles 19 Cell Organelles Ribosomes Endoplasmic reticulum Sarcoplasmic reticulum Golgi apparatus Mitochondria Lysosomes Endosomes Peroxisomes Proteasomes 20 Ribosomes Sites of protein synthesis Composed of a large subunit and a small subunit Subunits assemble with each other and mrna to form functional ribosome 21

8 22 Ribosomes Free ribosomes Free in the cytoplasm Synthesise proteins used inside the cell Attached ribosomes Associated with an intracellular membrane complex (endoplasmic reticulum) Produce proteins that are secreted from the cell 23 Endoplasmic Reticulum Network of membranes, continuous with the membrane of the nucleus, distributed throughout the cytoplasm of the cell Consists of broad, flattened interconnecting sacs and tubules Cisternae (interior of sacs and tubules) isolated from rest of cytoplasm 24

9 Endoplasmic Reticulum 25 Endoplasmic Reticulum Rough Ribosomes attached Proteins produced and modified by these ribosomes for secretion and internal use Smooth No ribosomes attached Manufactures Lipids Help form vesicles Contribute to plasma membrane Carbohydrates Changes structure of chemicals and drugs, reducing toxicity 26 Sarcoplasmic Reticulum Smooth endoplasmic reticulum known as sarcoplasmic reticulum in muscle Stores calcium for muscle contraction 27

10 Golgi Apparatus Flattened, membranous sacs containing cisternae stacked on top of each other Modifies, packages and distributes proteins and lipids manufactured by rough and smooth ER 28 Mitochondria Provide energy for the cell power plants Produce ATP primary source of energy for most reactions in cell Mitochondria increase in number when cell energy requirements increase. Mitochondria contain DNA that codes for some of the proteins needed for mitochondria production. 30

11 Mitochondria Outer membrane Smooth Intermembrane space Inner membrane Infolds (cristae) Enzymes of electron transport chain Matrix Enzymes of Kreb s cycle 31 Lysosomes Vesicles formed at the Golgi apparatus (and released from this to perform function) Contain hydrolytic enzymes that function as intracellular digestive enzymes Enzymes (made in endoplasmic reticulum) degrade proteins, nucleic acids, lipids, carbohydrates 32 33

12 Endosomes Membrane-bound vesicles Involved in internalisation of substances Types Phagocytosis Pinocytosis Receptor-mediated endocytosis Peroxisomes Smaller than lysosomes Contain enzymes to break down fatty acids and amino acids Hydrogen peroxide is a by-product of breakdown 36

13 Proteasomes Consist of large protein complexes Include several enzymes that break down and recycle proteins in cell 37