1 Chapter 4 Cell Structure & Function Topics:The Cell Eukaryotic Cells Multicellular Organization CPI BIOLOGY

2 The Cell Basic unit of an organism All living things composed of cells Robert Hooke (1665) – described plant cells using a microscope Anton van Leeuwenhoek (1673) – described animal cells using microscope Matthias Schleiden – botanist, Theodor Schwann – zoologist, Rudolf Virchow – biologist: were other early cell investigators

3 Cell Theory 1. All living things composed of cells 2. Cells are basic unit of structure & function in an organism 3. Cells arise only from pre-existing cells through reproduction

4 Diversity of Cells Size, Shape, Internal Organization 1.Size Size range for most cells ~ µm (0.002 in) Some bacteria as small as 0.2 µm ( in) Some cells as large as 6.5 ft (nerve cell in giraffe’s leg) Cell growth limited by ratio of outer surface area to volume; as cells get larger, the surface area becomes too small to support cell volume Side lengthSurface areaVolumeRatio (A:V) 1mm6mm 2 1mm 3 6:1 2mm24mm 2 8mm 3 3:1 3mm54mm 2 27mm 3 2:1

5 2. Shape Shape diversity reflects functional diversity Nerve cells – long extension for transmission/reception of impulses Skin cells – flat for covering body RBCs – aneucleated, donut shaped to squeeze through capillaries 3. Internal organization Cells contain organelles (component performing a specific function) Cell membrane – surrounds cell and nucleus Nucleus – “command center”, contains DNA Prokaryotes – no nucleus Eukaryotes – have a nucleus

6 Classification Scheme Kingdom5 Kingdoms PhylumMonera ClassProtista OrderFungi FamilyAnimalia GenusPlantae Species Subspecies (animals) Variety (plants)

7 Prokaryote v. Eukaryote Autotroph v. Heterotroph Prokaryotes – one-celled organisms having NO nucleus, DNA is present, organelles NOT present Eukaryotes – one-celled to multi-celled organisms having a nucleus, DNA enclosed by nucleus & separate from cell contents, contain organelles Autotroph – make food from photosynthesis or chemiosynthesis Heterotroph – “eats” food

8 5 Kingdoms Monera Unicellular prokaryotes Protista Unicellular eukaryotes Fungi Uni- & Multicellular eukaryotic heterotrophs (decomposers) Animalia Multicellular eukaryotic heterotrophs Plantae Multicellular eukaryotic autotrophs

9 Cell Organelles: Eukaryotic Animal Cells 1. Cell membrane 2. Mitochondria 3. Ribosome 4. Endoplasmic reticulum 5. Golgi apparatus (body) 6. Lysosomes 7. Cytoskeleton 8. Cilia/Flagella 9. Nucleus

10 Animal Cell

11 1. Cell Membrane Allows substances in/out of cell Fluid-mosaic model – acts like a fluid Selectively permeable Composed: phospholipid bilayer Hydrophilic heads point out Hydrophobic tails point in Other molecules imbedded into bilayer Peripheral proteins (on surface of membrane) Integral proteins (embedded inside membrane) Steroids (help stabilize membrane) Carbohydrates (attached to surface proteins, function as attachment sites)

12 Cell Membrane

13 2. Mitochondria Cell powerhouse Reactions in this organelle produce ATP Double membrane bound Folded inner membrane, cristae Contains own DNA (mitochondrial DNA) High E requiring cells have lots of mitochondria; typical liver cell has 2500 mitochondria

14 Mitochondria

15 3. Ribosomes Site of protein synthesis Not membrane bound Composed of proteins + RNA Sometimes attached to endoplasmic reticulum; sometimes floating free in cell Proteins for use within cell produced by free ribosomes Proteins for export from cell or to be used in cell membrane produced by ribosomes embedded in endoplasmic reticulum

16 Ribosome

17 4. Endoplasmic Reticulum (ER) Cellular “highway” – how many of the cell products move about the cell; series of channels within cell Rough ER – has ribosomes embedded in it; proteins made on ribosome & transported thru ER Smooth ER – has no ribosomes Functions: synthesis of steroids, regulation of Ca ++ levels in muscle cells, breaks down toxins in liver cells

18 Endoplasmic Reticulum

19 5. Golgi Apparatus (Body) Processing & packaging organelle Sac-like structures attached to ER Proteins & other substances made in the rough ER are packaged into membrane- bound organelles for export from cell

20 Golgi Body

21 6. Lysosomes “Policemen” of the cell, help regulate things Small, spherical, contain hydrolytic enzymes Break down proteins, carbohydrates, lipids, DNA, RNA, dead organelles, viruses, bacteria Decomposers (fungi) have many lysosomes to breakdown substances

22 Lysosomes

23 7. Cytoskeleton Internal support structures in cell; aids in movement of organelles in cell Composed of protein strands Microfilaments – small strands Microtubules – large strands Actin – a protein in microfilaments;contribute to cell movement & have a role in muscle contraction Spindle fibers – composed of microtubules, role in cell division (move chromosomes)

24 Cytoskeleton

25 Cilia/Flagella Assist movement Extend from cell surface Cilia – many short filaments Aid in moving cell Aid in moving substances around cell Flagella – one to few long filaments Aid in moving cell

26 Cilia Ciliated protist   Human nasal cilia

27 Flagella  Flagellated bacterium  Human sperm

28 Nucleus Cell control center – directs cell activities Membrane bound – nuclear envelope Nuclear pores allow substances in/out DNA remains in nucleus Contain DNA Site where RNA is made Nucleolus – site where ribosomes made

29 Nucleus

30 Plant Cells Structures/organelles common to animal eukaryotic cells are common to plant eukaryotic cells, except plants have 3 additional structures Structures: Cell Wall Vacuoles Plastids

31 Plant Cell

32 1. Cell Wall Rigid, lies outside cell membrane Composed of cellulose Pores allow ions, molecules in/out of cell 2 types of cell walls: Primary Forms in young plant cells, grows w/ cell Secondary Forms in adult plant cells, occurs between cell membrane & 1º cell wall, woody & had definite shape, does not allow further growth

33 2. Vacuoles Storage organelles, fluid filled Contain various substances Water Enzymes Metabolic wastes Cell products Large, often taking up as much as 90% of cell volume

34 3. Plastids Storage organelle containing starch, fats, or pigments Similar to mitochondrion in structure, double membrane bound Inner flattened membranes - thylakoids Chloroplast – type of plastid containing pigment chlorophyll Function – site of photosynthesis Other plastids contain other pigments like carotene which give plants the characteristic orange color

35 Chloroplast Of what organelle does this remind you?

36 Levels of Organization Levels: Cell Tissue Organ Organ system Organism Some organisms are unicellular Many organisms are multicellular Evolution of uni- to multicellular and of prokaryote to eukaryote

37 Prokaryote to Eukaryote Dr. Lynne Margulis proposed the “endosymbiotic” theory 2 to 1.5 bya, small aerobic prokaryotes invaded larger anaerobic prokaryotes and successfully managed to maintain a symbiotic relationship Aerobic prokaryotes inside the “host” prokaryotes gave rise to modern mitochondria Aerobic autotrophic prokaryotes inside “host” prokaryotes gave rise to modern chloroplasts

38 Unicellular to Multicellular Theorized that early unicellular eukaryotes began to associate with others & live in groups These groupings of similar organisms may have formed colonies in which the functions necessary for life became shared between the organisms For example: some became specialized for locomotion, some for respiration, some for reproduction, etc. These may then have evolved into early multicellular organisms Volvox is a colonial organism composed of 500 – 60,000 cells which maintain an individual existence, yet each cell has a specific function to aid the colony (mainly reproduction or locomotion)

39 Volvox