Cellular Level of Organization

1. Cellular Level of Organization Chapter 3

2. Overview: fundamental units of life • All organisms are made of cells • Cell is the simplest collection of matter that can live • Cell structure is closely related to cellular function • All cells come from pre-existing cells

3. How do we study cells? • Study of cells –cytology • Microscopes and biochemistry have revealed much about cell structure (1665-Robert Hooke found the cell) • Two classes of cells in human body: sex cells and somatic cells

4. I. Basic features include: • Plasma membrane • Semifluid substance called cytosol (cytoplasm) • Chromosomes (carry proteins) • Ribosomes (make proteins) • DNA in a nucleus bound by membranous nuclear envelope • Membrane bound organelles • Cytoplasm in region btwn plasma membrane & nucleus

5. A. Cell (plasma) Membrane- separates cell contents from interstitial fluid 1.Extracellular fluid- fluid outside of the cell 2. Interstitial fluid- extracellular fluid found in most body tissues 3. General functions include: • physical isolation- inside of cell is different from outside • regulates exchange- controls ion and nutrient entry and waste elimination • sensitive to pH changes, ion concentrations • provides structural support

6. 4. Membrane structure • Made up of lipids, proteins, carbohydrates • Is a double membrane, made of a phospholipids bi-layer • Hydrophilic heads at surface, hydrophobic tails (hate water) inside 5. Membrane proteins- function as: • Anchors: attach to other structures • Identifiers: immune system • Enzymes: catalyze reactions • Receptor proteins: respond to specific EC material • Carrier proteins: transport across cell membrane • Channels : permits movement of H2O and solutes across membrane

7. 6. Membrane carbohydrates • Glycocalyx functions: • Form layer that lubricates and protects membrane • Anchor cell in place • Functions as receptor

8. B. Cytoplasm- general term for material between plasma membrane and nucleus • contains cytosol and organelles • has higher concentration of potassium, more suspended proteins than extracellullar fluid • has small reserves of amino acids and lipids, e.c. fluid does not (transports only)

9. Organelle Classifications Non Membranous Membranous In direct contact w/ cytosol Includes: cytoskeleton Microvilli Centrioles Cilia ribosomes Lipid membrane separates from cytosol Includes: mitochondria endoplasmic reticulum golgi apparatus lysosomes peroxisomes nucleus

10. II. Non-Membranous organelles: A. The cytoskeleton 1. Has 4 components: a. Microtubules: • found in all cells • provide strength, anchor organelles • aiding in cell movement, help form spindle apparatus for cell division • structural components of centrioles b. Thick filaments: • massive bundles of protein myosin, abundant in skeletal and cardiac muscles (both contract)

11. c. Intermediate filaments: • provide strength • stabilize organelles • transport materials w/in cytoplasm d. Microfilaments: • slender proteins made up of actin. • anchor cytoskeleton to integral proteins of cell membrane and interact w/ filaments to change cell shape

12. B. Microvilli- small finger like projections, increase surface area of cell, found in areas of absorption (digestive tract) C. Cillia- beat fluid and mucus across cell surface (respiratory tract) D. Flagella- longer than cilia, whip like, moves cell through fluids (sperm cells only example of human cells)

13. E. Ribosomes 1. manufacture proteins from information provided by DNA 2. free ribosomes send proteins into cytoplasm 3.while fixed ribosomes send proteins to ER F. Centrosome (central body) – 1. Usually near the G.A. and nucleus 2. Composed of 2 "cylinders" called centrioles (each composed of numerous microtubules) which always lie perpendicular to each other. 3. Active involved in cell reproduction - SPINDLE forms from the centrioles

14. ER Ribosome

15. III. Membranous organelles • Endoplasmic reticulum 1. network of membranes that connect to the nuclear envelope surrounding the nucleus 2. Has four functions: • Membrane makes proteins, carbohydrates, lipids • Can store molecules made in cytosol • Materials travel from place to place in the ER • Neutralizes drugs and toxins

16. 3. ER forms hollow tubes and chambers called cisternae 4. Smooth ER a. no ribosomes on surface b. functions include - production of phospholipids & cholesterol needed for maintenance of plasma membrane - synthesis of sex hormones in reproductive organs

17. - synthesis and storage of glycerides (especially in liver & fat cells) -storage of glycogen in skeletal muscles & liver cells 5. Rough ER - have ribosomes on surface - functions as workshop/shipping center - proteins made here are modified and packaged for export to golgi apparatus

18. - most proteins are packaged into membranous sacs that pinch of the tips of the cisternae - these sacs are called transport vesicles, and deliver the contents to the golgi apparatus - the amount of SER and RER varies w/ cell type

19. B. Proteasomes 1. small organelles that remove the proteins produced into cytoplasm by free ribosomes 2. responsible for removing and recycling damaged and abnormal proteins. C. Golgi apparatus- shipping and receiving center 1.Consists of flattened membranous sacs (cisternae) that are like 5 or 6 plates 2. Functions include: -modifies & packages secretions for release from cell (hormones or enzymes)

20. -Sorts and packages materials into secretory vesicles that fuse with the plasma membrane and empty compounds into E.C. fluid (process is called exocytosis) -Renewal of cell membrane- when secretory vesicles fuse with the plasma membrane, they add new lipids & protein -Produce lysosomes: vesicles that remain in the cytoplasm and contain digestive enzymes

21. Golgi apparatus

22. D. Lysosomes- vesicles filled with digestive enzymes -Function as defense against disease • Destroy damaged or dead cells (autolysis) • -provide isolated environment for dangerous chemical reactions E. Peroxisomes- smaller than lysosomes - absorb and breakdown fatty acids, neutralize toxins (alcohol) -Protect cells from free radicals during reactions

23. F. Mitochondria 1. small structures responsible for energy production a. vary in shape : can be long, short, slender, or fat b. # of mitochondria in cells depends on the cell’s energy demands- ex: not found in red blood cells, but makeup 30% of the volume of a cardiac muscle cell 2. have an unusual double membrane, with the outer membrane surrounding the organelle, and the inner membrane forming cristae- folds that increase the surface area inside the organelle

24. 3. Cristae increase the surface area of exposed fluid, called the matrix a. metabolic enzymes in the matrix catalyze reactions that provide energy for the cell 4. Cells must store energy in a way that can be moved from place to place w/in the cell a. ATP & ADP is how cellular energy is stored, in high energy bonds and compounds. b. cells break the bonds, converting ATP to ADP and release energy for cell to use

25. 5. Mitochondrial energy production a. glycolysis (first step takes place in the cytosol) - glucose moleucle is broken into 2 molecules of pyruvic acid. Pyruvic acids are absorbed by mitochondria b. In the matrix inside the mitochondria, a CO2 molecule is removed from each pyruvic acid, the remainder enters the Krebs cycle c. the Krebs cycle is a pathway that breaks down the pyruvic acid in the presence of oxygen

26. d. the remaining carbon & oxygen are released as CO2 from the cell e. the hydrogen atoms go through an electron transport chain that releases energy, converting ADP to ATP f. because this process requires oxygen, it is known as aerobic metabolism or cellular respiration g. this produces about 95 % of the ATP needed to keep the cell alive

27. G. Nucleus 1. Characteristics: a. largest, most observable structure of the cell b. serves as the control center: stores info needed to direct the synthesis of over 100,000 different proteins in the human body b. Contains genetic material

28. 2. Structure a. surrounded by a selectively permeable double membrane called the nuclear membrane (envelope) b. Nuclear pores in the membrane serve 2 functions i. let ions & small molecules in/out ii. keep DNA & proteins inside

29. Filled with fluid called nucleoplasm contains: i. the nuclear matrix, a network of filaments that provide structure & may regulate genetic activity d. nucleolus- most nuclei have several small, dense structures within nucleus i. synthesize ribosomal RNA, assemble ribosomal subunits which get to the cytoplasm through the nuclear pores ii. composed of RNA, enzymes, and proteins called histones iii. Form around portions of DNA that contain instructions for making ribosomal proteins

30. e. DNA- stores the instructions for protein synthesis i. interactions btwn DNA & histones help determine info available to the cell ii. DNA wind around histones, forming nucleosome- this allows DNA to be packed into a small area iii. In cells that are not dividing, the tangle of nucleosomes are called chromatin iv. Coiling becomes tighter before cell division, forming distinct structures called chromosomes (23 pairs in somatic cells, 24 pairs in sex cells)

31. IV. The Genetic Code • Information storage in the nucleus • Each protein molecule consists of a unique sequence of amino acids • The sequence for all the proteins is stored in the DNA strands • The chemical language the cell uses is called the genetic code B. A DNA molecule has a pair of strands held together by weak hydrogen bonds (btwn complementary nitrogen bases) 1. information is stored in the sequence of nitrogenous bases along the length of the DNA molecule

32. 2. Nitrogen bases are: a. Adenine/Thymine –these two pair b. Guanine/Cytosine-these two pair 3. Three nitrogenous bases form a triplet code called a codon (CCG would code for a certain amino acid) 4. A gene is functional unit of heredity: it contains all the DNA triplets needed to produce specific proteins

33. C. Transcription- to copy, rewrite • Gene activation- process in which a portion of the DNA molecule is uncoiled and histones are removed • RNA polymerase binds to promoter (start signal) to begin transcription- process where RNA (ribonucleic acid) is made from a DNA template • Messenger RNA(mRNA) forms so info in DNA can be carried to cytoplasm where proteins are synthesized a. RNA “copies” one side of DNA strand: b. Bases match (A-T, C-G except in RNA, Uracil is used in place of Thymine) c. Bases are copied and DNA strands reattach behind moving strand

34. d. RNA codons are complementary to DNA: example • CGA TGG CAG e. Transcription stops at a “Stop signal” enzyme (polymerase) and mRNA detach, DNA strand closes f. Nonsense regions (introns ) are cut out and parts of code that make sense (exons) are pasted together to create a shorter strand that can move to the cytoplasm

35. D. Protein synthesis is the assembling of functional untis of polypeptides in the cytoplasm, and occurs through translation: 1. translation- the formation of a chain of amino acids, made by changing the message in the mRNA from codons to amino acids a. Ribosome reads mRNA message b. Each codon asks for 1 amino acid c. The Transfer RNA (tRNA) are mobile- they bind and deliver the correct amino acid

36. d. It does this by binding to the mRNA, and copying the codon as an anticodon e. The anticodon of the tRNA bonds with the correct amino acid, process is repeated w/a second tRNA f. Amino acids are connected together by a peptide bond g. Amino acids are added until ribosome reaches the “stop” codon, then ribosome units detach and amino acids form protein

37. V. Diffusion and Transportation Process A. Plasma membrane 1. barrier that isolates cytoplasm form extracellular fluid 2. conditions inside cell can be different from those outside of the cell 3. how do nutrients & waste products get across the plasma membrane without reducing its effectiveness as a barrier? a. it is selectively permeable- permits free passage of some materials, and restricts the passage of others

38. b. whether allowed in or out of cell depends on size, shape, electrical charge, lipid solubility B. Passive Transport- allows ions/molecules across the membrane with out energy from the cell 1. diffusion- molecules become evenly spaced, and move from area of higher concentration to areas of lower concentration a. simple diffusion- alcohol, fatty acids, dissolved gases (CO2 & O2), & lipid- soluble drugs diffuse easily through the phospholipid bilayer

39. b. tries to eliminate concentration gradient, difference btw high/low and low concentration c. rates of diffusion are effected by • distance- more distance means longer time • size of gradient- larger gradient means faster diffusion • molecule size- larger is slower • temp.- higher temper, faster

40. d. channel-mediated diffusion: allow ions and water-soluble compounds that aren’t lipid soluble to enter or leave the cytosol through a membrane channel - membrane channels are small passageways created by transmembrane proteins e. osmosis- type of diffusion involving the movement of water • water moves from high concentration to low • occurs when membrane is permeable to water, but not freely permeable to solutes • water moves toward high concentration of solutes because that is where water concentration is lower

41. Osmolarity- total solute concentration in a solution • isotonic- no movement of water in or out of the cell • hypertonic- movement of water out of cell, cell usually shrinks, ex: crenation, RBC shrinks • hypotonic- movement of water into cell, cell may rupture, ex: hemolysis, rupture of RBC

42. C. Other types of transport 1. filtration- pressure forces fluids and solutes across a membrane, passive 2. carrier- mediated transport- requires special integral protein, may be passive or active 3. vesicular transport- movement of materials in small sacs, active

43. VI. Cell Life Cycle A. Cell division- process where a cell divides to increase size and complexity of organism 1. cells can be damaged by wear and tear, toxic chemicals and temp. changes 2. cells age just like us, life spandof hours to decades 3. the genetically controlled death of a cell is called apoptosis 4. mitosis is the division of somatic cells 5. meiosis is the division of sex cells

45. B. Life Cycle of Somatic Cell • Interphase- growth and development: cells spend most of lives in this phase - divided into Go, G1, S, and G2 phases a. G1 phase- cell manufactures mitochondria, cytoskeletal elements, ER, centrioles, ribosomes, cytosol, golgi membranes -may last 8-12 hrs, others may last weeks or months, in which cell carries on normal functions b. S phase: DNA replication- 6-8 hours, cell duplicates its chromosomes and copies its DNA, producing one set of chromosomes for each new cell.

46. c. G2 phases- last phase, 2-5 hours d. M phase- mitosis- separates duplicated chromosomes of the original cell i. Prophase- begins when chromosomes coils tightly, become visible as individual structures. Each copy is called a chromatid, and they are connected at centromere ii. centrioles move to the poles, extend spindle fibers Prophase ends w/disappearance of nuclear envelope

47. iii. metaphase- spindle fibers enter the nuclear region, attach to chromatids, and line up at the metaphase plate (equator) iv. anaphase- begins when chromatid pair split, 2 daughter chromosomes are pulled to the poles; ends when daughter chromosomes are near centrioles at poles

48. v. telophase- cell prepares to return to interphase state -Nuclear membrane forms, nuclei -enlarge, chromosomes uncoil vi. cytokinesis- splitting the cytoplasm in cell division starts in late anaphase, ends in telophase after the nuclear membrane has formed

49. C. Process of Replication 1. the cell duplicates its chromosomes- S phase of interphase 2. involves the replication of DNA a. The DNA strands unwind, DNA polymerase attaches on both sides, and produces a complementary (new, opposite) copy b. On one strand, the copy is produced as a continuous strand (works toward the zipper of the DNA original strand)- leading strand c. On the other, it’s produced in short segments, and is then linked together ( works away from the zipper) by the enzyme ligase- lagging strand

50. d. Both finished strands of DNA are composed of one original side, and one new complementary side D. Mitotic Rate and energy use 1. start of mitosis –recognizable, chromosomes become highly visible 2. Cells w/ longer life have slower the mitotic rate (rate of division); muscle cells & neurons never divide or under special conditions only 3. short lived cells, like those covering the surface of the skin or lining the digestive tract are subject to attack by chemicals, pathogens, and abrasion; surviving for only days