Cell Structure and Function

1. Cell Structure and Function College Prep Biology Mr. Martino

2. Introduction • Antony van Leeuwenhoek (Dutch) – observed nature through lenses and documented • Galileo Galilei (Italy) – developed the first microscope in early 17th century • Robert Hooke (England) - first to observe (and name) cells – mid-17th century • Robert Brown – 1820’s observed the nucleus

3. Intro – Cell Theory • Matthias Schleiden – (botanist) 1838 all plants are made up of cells, the smallest unit of life • Theodor Schwann – (zoologist) 1839 all animals are made up of cells, the smallest unit of life • Rudolf Virchow – (physiologist) 1849 realized life arises directly from the growth and division of single cells • Together these concepts developed into the Cell Theory: • 1. All organisms are composed of at least one cell • 2. Cell is the basic unit of structure and function in life • 3. Cells come from preexisting cells

4. 6.1 Basic Aspects of Cell Structure & Function • Cell: smallest unit that retains the properties of life • All differ in size, shape, function, etc. • All are alike in 3 ways: • 1. Plasma (cell) membrane: thin, outermost membrane which regulates what enters and leaves • 2. DNA – containing region: DNA and RNA are located within the cell for reproduction • 3. Cytoplasm: semi-fluid matrix containing ribosomes and organelles (if present) which is located between the plasma membrane and DNA

5. 6.1 Basic Aspects of Cells - con’t • Eukaryotic Cells: more complex cells which contain membrane-bound organelles • Prokaryotic Cells: no true nucleus and lacks most of the cellular organelles • Only bacteria cells

7. 6.2 Fluid Mosaic Model • Cell membrane is referred to as the fluid mosaic model • It moves laterally - fluid • has many components throughout - mosaic • Structure is a lipid bilayer – consisting of 2 layers of phospholipids • polar, hydrophilic head • 2 nonpolar, hydrophobic unsaturated fatty acid tails

8. Fluid Mosaic – con’t • Many different components spread throughout membrane – mosaic • Phospholipids (main), glycolipids, sterols (cholesterol in animals), and proteins • Proteins are varied – many enzymes, transport, hormones, recognition, and adhesion

9. 6.3 Cell Size and Shape • Most cells are too small to see without a microscope • Various shapes are result of function – very diverse • Surface-to-volume ratio is very important • Cells need plenty of cell membrane (surface area) to allow enough nutrients in and to remove the waste • When cells grow, the insides (volume) grows much faster than the s.a. • Most cells must stay small – large cells will divide

10. Microscopes • Micrograph: photo taken through a microscope • Light Microscope: pass a beam of light through specimen to enlarge image • Specimen must be small • Only magnifies about 1000X • Electron Microscope: use a beam of electrons • Cannot observe living organisms – must be in vacuum • Scanning: (SEM) only studies surfaces of structures • Transmission: (TEM) studies internal structures

11. 6.5 Eukaryotic Cells • Eukaryotic Cells: more complex cells which contain membrane-bound nucleus and organelles • Include cells in plants, animals, fungi, and protistans • Organelle: internal, membrane-bound sac that serves one or more specialized functions in cell • Separate organelles permits many activities to occur simultaneously in a small space

12. Cell Structure & Function due to Proteins • DNA – codes for proteins • Eukaryotic cell DNA is contained in a nucleus • Nuclear envelope: double membrane layer (2 lipid bilayers) that separates the nucleus from cytoplasm • Nuclear pore: opening in nuclear envelope that allows certain things to enter and leave nucleus

13. Nucleolus: dense, dark mass in nucleus that makes protein and RNA – two subunits which later become ribosomes • Chromatin: cell’s collection of DNA • Chromosome: one DNA molecule and proteins • Nucleoplasm: fluid interior of nucleus

15. 6.7 Cytomembrane System • Cytomembrane system: series of organelles in which lipids are assembled & proteins are made • Includes endoplasmic reticulum, Golgi bodies, and vesicles • Endoplasmic reticulum: a series of stacks of flattened sacs extending from nucleus through cytoplasm • Rough: ribosomes attached and synthesizes proteins • Smooth: no ribosomes and synthesizes lipids

16. Cytomembrane con’t • Golgi bodies: consists of a series of flattened sacs and contains enzymes that complete and package proteins and lipids into vesicles • Vesicles pinch off and take contents to where needed

17. Cytomembrane – con’t • Vesicles: tiny, membranous sacs in cytoplasm • Includes lysosomes and peroxisomes • Lysosomes: contain powerful enzymes and digest proteins, carbohydrates, nucleic acids, and some lipids • Peroxisomes: contain enzymes that breakdown fatty acids and amino acids – forming H2O2

19. 6.8 Mitochondria • Mitochondria: forms energy-carrying ATP molecules • Only found in eukaryotic cells • Double-membrane system • Have their own DNA and divide on their own

20. 6.9 Plant Organelles • Chloroplasts: convert sun’s E into chemical E of ATP which is used to make sugars • Found in photosynthetic plant cells • Two outermost membranes and one inner membrane – thylakoid • Thylakoids are surrounded by a fluid – stroma • Contains pigments – mostly chlorophylls (green) • Chromoplasts: contain carotenoids which are pigments that make flowers, leaves, and fruits red, orange, & yellow • Amyloplasts: lack pigment & store starch

22. Central Vacuole: large, fluid-filled organelle in plant cells • Stores amino acids, sugars, ions, and toxic wastes • Fills with fluid and enlarges cell size • Takes up to 50 – 90 % of cell

23. Cytoskeleton: a system of interconnected fibers, threads, and lattices • Provides internal organization, shape, and ability to move • Microtubules: hollow protein tubes used for movement • Microfilaments: twisted protein chains used for movement • Allow for movement by sliding or stretching

24. Flagellum: ring of microtubules used for locomotion • Tend to be long and whiplike • cells have only a few at the most • Cilium: ring of microtubules used for locomotion • Tend to be very short • If present, cells have many of them • Centriole: barrel-shaped structure that produces microtubules

27. 6.10 Cell Surface Specializations • Cell wall: protects and supports cells • Surrounds cell membrane • Primary – sticky, thin and pliable composed of pectin, glycoprotiens, and cellulose • Secondary: in mature cells, no longer growing composed of cellulose and sometimes lignin

28. More Cell Surface Specializations • Cell to Cell Junctions: used for communication between cells of tissues • Plasmadesmata: channels that interconnect cytoplasm of plant cells • Tight junctions: link epithelial cells of animals • Line tissues & organs & seal • Adhering junctions: join tissues that stretch • Heart, skin, etc. • Gap junctions: link cytoplasm of neighboring cells

29. 4.11 Prokaryotic Cells • Prokaryotic Cells: no true nucleus and lacks most of the cellular organelles • Only bacteria cells • Very small • Nucleoid region: area where DNA is located • Also have ribosomes (protein synthesis) • plasma membrane (regulation) • Many have cell wall (protection and support) • capsule (protection and adhesion) • pili (adhesion) • flagella (locomotion)