Cell Structure and Function Chapter 4 Biology 100

1. Cell Structure and FunctionChapter 4Biology 100

2. Discovery of the Cell • Robert Hooke used a simple kind of microscope to study slices of cork in 1664. • He saw many cubicles fitting neatly together • Hooke called these cells. • van Leeuwenhoek was the first to see living cells and later was first to see bacteria Van Leeuwenhoek’s microscope

3. The Cell Theory • Schleiden and Schwann came up with the theory in the 1830’s • All living things are made of cells • Virchow added in 1855 to the cell theory • New cells are formed only from division of pre-existing cells, not spontaneous generation

4. Differences and Similarities of Cells • All cells are surrounded by a plasma membrane (cell membrane) which is selectively permeable to materials. • Prokaryotes lack a true nucleus as well as internal membrane-bound organelles. • Bacteria • Eukaryotes have a true nucleus and have at least one membrane-bound organelle • Include plant, animal, fungi, protozoa and algae cells

5. Cell Size • Prokaryotic cells can be 1-10 μm, while eukaryotic cells are 10-100 μm. • Some eukaryotic cells are quite large, like the yolk of a chicken egg • Two organelles found in eukaryotes, the mitochondrion and the chloroplast, are similar in size to most bacteria.

6. Cell Size • The ratio of surface area to cell volume limits cell size because it reflects the balance between supply rate and supply demand. • The surface area determines the rate at which materials diffuse into or out of the cell. • For a cell of a constant shape, for every time the surface area increases by L2, volume increases L3

7. Prokaryotes • Prokaryotes have no true nucleus or membrane-bound organelles, have a nucleoid region • Has a Cell Wall, and some may have a capsule, which encloses the cell wall • Forms of movement are the flagella and/or the pilli • Contains ribosomes where protein synthesis occurs

8. Prokaryotes • Bacteria cells have different shapes • Rod-shape • Spherical shape • Spiral

9. Eukaryotes • Eukaryotes, unlike prokaryotes, have a true, membrane-bound nucleus. • Contain a variety of organelles, specialized membrane-bound structures where cell processes occur

11. Endoplasmic Reticulum • Endoplasmic Reticulum (ER) is where proteins and lipids are synthesized • Large surface area • Rough ER is embedded with ribosomes • Ribosomes are nonmembranous organelles that help with synthesis of proteins • Smooth ER is where lipids are synthesized, detox

12. Golgi Apparatus • Golgi Apparatus are smooth, flattened membranous sacs • Collects, packages and distributes molecules manufactured in the cell • Animals contain around 20 complexes, plants have hundreds.

13. Vesicles and Vacuoles • Tiny, membranous sacs known as vesicles deliver molecules to and from the Golgi Complex, vacuoles are larger structures that perform the same tasks • Some go from ER to the Golgi Complex • Some go to other organelles in cell • Others will go to plasma membrane and combine with it • May contain insulin, enzymes, etc. to go outside the cell • In plants, some vesicles have cellulose to make new cell wall material • Some vesicles contain enzymes to breakdown various molecules

14. Fig. 4.11, pg. 77. Lysosome • A lysosome is a tiny vesicle that buds off the Golgi Apparatus and contains enzymes that break down macromolecules, for digestion and destruction • These enzymes function best at a pH of 5 • Hydrogen ions are transported into lysosome to create this acidic environment • Will also destroy bacteria, viruses and fungi

15. Peroxisome • A peroxisome is an organelle that has the enzyme, catalase, that breaks down hydrogen peroxide, H2O2 • Breaks down fatty acids into 2 carbon fragments • n addition it includes enzymes which synthesize cholesterol and bile acids. • Is not formed in the Golgi apparatus • Aids chemical reactions, including the breakdown of fatty acids, synthesis of cholesterol and synthesis of lipid molecules

16. Ribosomes • Ribosomes are constructed from two subunits, which are composed of ribosomal RNA and proteins. • Ribosomes synthesize polypeptides from free amino acids, according to the instructions on messenger RNA. • Ribosomes are like CD players, producing music (proteins) according to the instructions on the CD (mRNA).

17. Nucleus • The nucleus is surrounded by two membranes, the nuclear envelope • Protein complexes at nuclear pores regulate the entry of large macromolecules into and out of the nucleus • The nucleus contains most of the DNA in a cell.

18. Nucleus • The primary function of the nucleus is to transfer the information for the synthesis of proteins from DNA to RNA. • The nucleolus is a dense area within the nucleus with DNA fragments, ribosomal RNA, and proteins. • The nucleolus organizes the RNA and proteins into the ribosomal subunits.

19. Mitochondria • Mitochondrion (singular) has two membranes • Outer membrane is relatively simple, but the inner membrane is highly folded, a structure called cristae • Cristae are rich in enzymes for electron transfer and ATP synthesis

20. Mitochondria • The matrix is a fluid filled space inside the inner membrane • It contains soluble enzymes for aerobic cellular respiration. • The matrix also contains DNA (mtDNA), RNA, and ribosomes.

21. Mitochondria • Known as the powerhouse of the cell • It converts the energy stored in organic molecules to forms usable to the cells, especially production of ATP • Food + O2 → CO2 +H20 + Energy (ATP)

22. Chloroplasts • Chloroplasts are also surrounded by two membranes. • The outer and inner membranes, and intermembrane space are barriers, but play no specific functional role in photosynthesis. • Inside the inner membrane is the stroma, an aqueous space. • Floating in the stroma are thylakoids, flat membranous sac.

23. Chloroplasts • The thylakoid membrane contains chlorophyll and other pigments, electron transfer molecules, and enzymes that trap the energy in sunlight - photosynthesis. • This energy is used to generate ATP and high energy electrons in the light-dependent phase of photosynthesis. • These molecules pass to the stroma where CO2 and H2O are converted into sugars.

24. Chloroplasts • The stroma also contains DNA (chDNA), RNA, and ribosomes. • In the stroma, DNA is transcribed to RNA and RNA is translated into some chloroplast proteins.

25. Cytoskeleton • Intermediate filaments are semi-permanent components of the cytoskeleton. • Intermediate filaments are semi-permanent components of the cytoskeleton. • Intermediate filaments maintain cell shape and attach to proteins in the cell membrane

26. Cytoskeleton • Microfilaments are built with the beadlike protein actin • During cell division, motor proteins pull actin filaments together, slicing the cytoplasm in half like string around a ball of dough. • In muscle cells, the motor protein myosin pulls together microfilaments during contraction.

27. Cytoskeleton • Microtubules are small tubes that are built with the protein tubulin. • During normal conditions, one of their functions is to act as roadways for motor proteins.

28. Cytoskeleton • Microtubules are also the central supports for cilia and flagella. • Covered by just the cell membrane, cilia and flagella extend from the cell. • Motor proteins push/pull on the tubules within the cilium/flagellum. • This causes them to move back and forth.

29. Cell Membranes • Phospholipids are the dominant molecule in membranes. • Phospholipids naturally assemble into a bilayer • The membrane’s center is hydrophobic because of the fatty acid tails. • The outer edges are hydrophilic because of the phosphate groups.

30. Fluid Mosaic of Membranes

31. Cell Transport • A membrane is a selectively permeable barrier • Single molecules that are nonpolar or only slightly polar can pass through the hydrophobic core without problems. • These include O2, N2, CO2, steroids, alcohols, fatty acids, and pesticides. • The cell cannot regulate movement of these molecules as they follow the rules of simple diffusion

32. Cell Transport • Single molecules that are polar or charged require a transport protein or channel protein to pass through the core. • These include H20, ions, sugars, amino acids, and proteins. • Their movements into / out of the cell can be regulated by modifying the proteins involved.

33. CellTransport • Materials can move pass membranes: • A) as single molecules (diffusion and active transport) or in large quantities (vesicular transport) • B) without input of energy (passive transport) or requiring energy (active transport) • C) without the help of a protein (simple diffusion) or with the help of a protein (facilitated and channel-mediated diffusion).

34. Diffusion • During diffusion, molecules move from areas of higher concentration to areas of lower concentration, “down” the concentration gradient. • At equilibrium, movements of molecules in one direction are balanced by movements in the opposite direction.

35. Diffusion • Diffusion rates depend on: • a) the distance over which molecules must move: • shorter (thinner membrane) = faster • b) the size of the molecule: • smaller = faster • c) the surface available for diffusion: • wider = faster • d) the speed that molecules are moving = temperature: • higher = faster • e) the concentration gradient between two points • greater concentration difference = faster.

36. Diffusion • Diffusion rates also depend on how permeable the membrane is to a particular kind of molecule • The diffusion rates of one type of molecule are independent of the concentrations of any other types of molecules • In simple diffusion, molecules move past the membrane through the lipid core.

37. Diffusion • In channel mediated diffusion, molecules pass the membrane through a protein pore.

38. Osmosis • Osmosis is the movement of “free” water down its concentration gradient. • Some water molecules surround solutes as part of spheres of hydration. • If a membrane is not permeable to that solute, then these water molecules cannot pass either. • A solution with few dissolved molecules (low osmolarity) will have more free water molecules than a solution with more dissolved molecules (high osmolarity).

39. Osmosis • Imagine that we have a selectively permeable membrane separating a 40% sugar solution from a 10% sugar solution. • There are more “free” water molecules on the 10% sugar side than there are on the 40% sugar side. • Because there are more “free” water molecules in the 10% side, water will move by osmosis (diffusion of water) to the 40% side.

40. Isotonic • If the concentration of dissolved materials is equal in the surrounding solution as in the cell, then no net movement of water occurs.

41. Hypertonic • If the concentration of dissolved materials is greater in the solution than in the cell, then water will leave the cell. The solution is hypertonic compared to the cell. • If the concentration of dissolved materials is lower in the solution than in the cell, then water will enter the cell. The solution is hypotonic compared to the cell.

42. Transport • Specific carrier proteins allow materials that are not hydrophobic to pass through a membrane. • In facilitated diffusion, the carrier protein allows molecules to move from high concentration to low concentration. • Osmosis, facilitated diffusion, and standard diffusion are all examples of passive transport. • movement of materials down a concentration gradient without expenditure of energy

43. Active tranpsort • Active transport is the movement of materials across a membrane against its concentration gradient. • Molecules are pumped from low concentration to higher concentration. • Active transport requires metabolic energy to do the pumping.

44. In exocytosis a membrane-bound sac (a vesicle) fuses with a membrane and dumps the fluid contents outside the membrane (usually outside the cell). • Endocytosis is the reverse of exocytosis. • A region of membrane forms a pocket around the external materials, pinches off a vesicle, and transports this material inside. • In phagocytosis, the materials being brought insides are solid particles. • In pinocytosis, the materials being brought inside are fluids.

45. Endocytosis and exocytosis • White blood cells actively use endocytosis and exocytosis in their role as defenders of the body from invaders. • When they detect a microbe, they extend fingers of membrane and cytoplasm to surround it. • When the membrane fingers meet, they fuse.