Chapter 2A

1. Chapter 2A Cells

2. Objectives • Overview of the Cellular Basis of Life • Define cell. Discuss cell diversity. • Discuss a generalized cell. List the three main parts of a cell and their functions. • The Plasma Membrane: Structure • Discuss the fluid mosaic model of membrane structure. • List and describe the plasma membrane specializations. • The Plasma Membrane: Functions • Discuss membrane transport. Differentiate between active and passive transport. • Compare and contrast simple diffusion, facilitated diffusion, osmosis, and filtration. • Compare and contrast primary and secondary active transport. • Discuss the differences and similarities between the vesicular transport processes. • Define the resting membrane potential. How is it created and maintained? • Identify the different ways a cell interacts with its environment. Discuss cell adhesion molecules and the roles of membrane receptors.

3. Objectives • The Cytoplasm • Discuss the cytoplasm and its components. • Discuss the functions of the cytoplasmic organelles. What conditions lead to a greater prevalence of a specific organelle? • The Nucleus • Define the characteristics and functions of the nucleus, nuclear envelope, and nucleoli. • Discuss chromatin structure and function. • Cell Growth and Reproduction • Identify the phases of cell growth and division, and describe what specific events occur within each phase. • Name the factors that influence cell division. • Define protein synthesis and the processes of transcription and translation. • Describe the types of RNA that are used in protein synthesis and their specific roles. • Discuss how proteins are degraded within the cytosol.

4. Objectives • Extracellular Material • Define extracellular material and list its components. • Developmental Aspects of Cells • Discuss how cell development progresses, and what signals stimulate these changes. • Discuss the various theories of cell aging.

5. Introduction • Robert Hooke • Cells=building blocks of the human body • Cell Theory=Cells are the fundamental units of all plant and animal tissues • Cells are the building blocks of all plants and animals • Cells are produced by the division of preexisting cells • Cells are the smallest units that perform all vital physiological fxns • Each cell maintains homeostasis at the cellular level • Homeostasis at the tissue, organ, organ system, and organism level reflects the combined and coordinated actions of many cells

6. Studying Cells • Cytology = study of the structure and function of cells • An Overview of Cellular Anatomy • 2 Classes of Cells: • Sex cells • Somatic cells • Cell surrounded by watery medium called extracellular fluid • Called interstitial fluid • Human cell contains three parts: • Nucleus: controls cell activity • Plasma membrane: fragile outer boundary • Cytoplasm: intracellular fluid packed with organelles • Cytosol= liquid • Organelles=intracellular structures, “little organs”

7. Overview • Cells are the structural units of all living things • Human body has 50-100 trillion cells

8. Chromatin Nuclear envelope Nucleus Nucleolus Plasma membrane Smooth endoplasmic reticulum Cytosol Lysosome Mitochondrion Centrioles Rough endoplasmic reticulum Centrosome matrix Ribosomes Golgi apparatus Microvilli Secretion being released from cell by exocytosis Microfilament Microtubule Intermediate filaments Peroxisome

9. Cell Membrane • Separates the cell contents from the extracellular fluid • Cell membrane= plasma membrane • Functions: • Physical isolation • Regulation of exchange with the environment • Sensitivity • Structural support

10. Cell Membrane • Membrane Structure • Thin and delicate 6-10 nm in thickness • Membrane Lipids • Lipids account for 42% of weight and proteins for 50% • Phospholipid bilayer • Hydrophobic tails (tails on inside) associated with other lipids like cholesterol • Hydrophilic heads (heads at the surface) • Cholesterol – stabilizes the membrane • Membrane is a fluid mosaic • Wedged between phospholipids

11. Cell Membrane • Membrane Proteins • Account for 55% of membrane weight • Classified by either position or function • Position: • Integral Proteins=part of the membrane structure • Some span the width of the membrane and are called transmembrane proteins • Peripheral Proteins=bound to inner or outer surface • Function: • Anchoring • Recognition • Enzymes • Receptor • Carrier • Channel (leak or gated)

13. Cell Membrane • Membrane Carbohydrates • Account for 3% of cell weight • Examples • Proteoglycans • Glycoproteins • Glycolipids • Glycocalyx [ “calyx” = cup ] • Carb portion that extends beyond the surface of the membrane • Functions • Lubrication & protection • Anchoring & locomotion • Specificity in binding • Recognition

16. Cell Membrane • Membrane Permeability • Permeability: Which substances enter or leave the cytoplasm • Impermeable • Freely permeable • Selectively permeable • Passage or transport can be passive or active • Passive = no energy required • Active = ATP required • 4 major categories: • Diffusion • Filtration • Carrier-mediated transport • Vesicular transport

17. Cell Membrane • Diffusion • HIGH  LOW concentration • Passive process • Diffusion across membranes • Pass through membrane channel if water-soluble • Cross lipid portion if lipid-soluble • Osmosis = net diffusion of water across membrane • Tonicity = relative solute concentration • Isotonic outside = inside • Hypotonic outside < inside (water flows in, cell lysis) • Hypertonic outside > inside (water flows out, crenation)

23. Cell Membrane • Filtration • Hydrostatic pressure forces water across a membrane • Example: capillaries • Carrier-Mediated Transport • Integral proteins bind to ions or organic substrates and carry them across the membrane • Facilitated Diffusion • Active Transport • Ion pumps • Sodium-Potassium Exchange Pump

29. Cell Membrane • Vesicular Transport • Materials move in/out via vesicles • Endocytosis • Receptor-mediated endocytosis • Pinocytosis • Phagocytosis • Exocytosis

32. Cell Membrane • Transmembrane Potential • Inside the cell has a slightly negative charge with respect to the outside of the cell  more cations outside, more anions inside • Opposites attract, but they’re separated by the membrane  TRANSMEMBRANE POTENTIAL (potential difference) • Unit of measurement is Volts (V) • Resting potential = transmembrane potential of undisturbed cell. • Ions held on either side of cell membrane have potential energy.

33. The Cytoplasm • Cytoplasm materials inside cell membrane and outside nuclear membrane • Cytosol = aka intracellular fluid • Organelles • Cytosol • Dissolved nutrients, ions • High concentration of suspended proteins (e.g. enzymes) • Small quantities of carbs, large reserves of amino acids & lipids • Carbs= energy • Amino acids make protiens • Lipids are energy reserve • Masses of insoluble materials (aka inclusions)

35. The Cytoplasm • Organelles • 2 Categories: • Non-membranous • Membranous • The Cytoskeleton • Microfilaments: slender protein strands made of actin • Intermediate filaments: intermediate size; most durable • Microtubules: hollow tubes made of the globular protein tubulin • Microvilli: small finger-like projections of cell membrane

36. The Cytoplasm • Centrioles  cylindrical structure composed of short microtubules • Cilia  composed of microtubules (9+2); anchored to basal body beneath cell surface; coordinated beating of cilia moves material across surface of cell • Flagella  “whip”; move a cell through ECF; sperm are only human cells with flagella

37. The Cytoplasm • Ribosomes: organelles that manufacture proteins • Two subunits: small ribosomal and large ribosomal • Composed of special proteins and rRNA • Two types • Free: scattered throughout cytoplasm • Fixed: attached to RER • Endoplasmic Reticulum: network of membranes connected to nuclear envelope • Four functions • Synthesis: proteins, carbs and lipids • Storage: • Transport • Detoxification: drugs and toxins absorbed and neutralized by enzymes. • Smooth ER – synthesize lipids and carbs, detox • Rough ER – fixed ribosomes, modify synthesized proteins and package them for transport to Golgi Apparatus

38. The Cytoplasm • Golgi Apparatus  flattened sacs; lie near nucleus • Three functions • Modifies/packages secretions for exocytosis • Renews/modifies cell membrane • Packages special enzymes for use within cell • Lysosomes  vesicles filled with digestive enzymes • Peroxisomes  contain enzymes produced at free ribosomes; absorb and break down fatty acids and other organic compounds

39. The Cytoplasm • Mitochondria • Double membrane • Cristae: folds in inner membrane • Powerhouse of the cell • Site of energy production • glycolysis occurs in cytosol, but its product (pyruvic acid) enter the mitochondria, where the TCA (citric acid cycle) occurs and ATP is produced • Process called aerobic metabolism

40. Organelles Review http://www.cellsalive.com/cells/cell_model.htm

41. The Nucleus • Nucleus is the control center • Most cells have single nucleus • Nuclear Envelope = double membrane, surrounds nucleus • Nuclear Pores = holes in envelope • Nucleoplasm = fluid contents of nucleus • Nucleoli = nuclear organelles that synthesize rRNA & assemble ribosomal subunits; composed of RNA, enzymes, and proteins

42. The Nucleus • Chromosome Structure • Chromosome = condensed/packaged DNA • Human somatic cells have 23 pairs of chromosomes • Chromatin = loosely coiled DNA, seen in non-dividing cell • DNA condenses into chromosomes prior to cell division • Two copies of each chromosome present • Each copy is a chromatid • Sister chromatids (two copies) joined together at the centromere, which is surrounded by protein complex called the kinetochore

43. The Nucleus • The Genetic Code • Genetic code = information stored in DNA strand • Genetic code = triplet code • Sequence of three nitrogenous bases • Each triplet codes for a specific Amino Acid • Gene = functional unit of heredity; contains all codons (triplets) needed to produce a specific protein • Each gene contains instructional segments: start and stop signals

44. The Nucleus • Gene Activation & Protein Synthesis • Gene activation = portion of DNA molecule unwinds, and complementary base pairs begin to separate • Transcription: DNA to mRNA • Template strand is used as a template for mRNA • Step 1 DNA strands separate, RNA polymerase (enzyme) attaches to template strand • Step 2 RNA polymerase reads the DNA sequence and makes a copy w/complementary base pairs, forming mRNA • Step 3 RNA polymerase reaches the stop codon, detaches itself and the mRNA strand

46. The Nucleus Translation: mRNA to aa chain Step 1 mRNA strand binds to small ribosomal subunit; start codon AUG signals translation to begin; tRNA (with complementary anticodon sequence UAC) brings first amino acid Step 2 small and large ribosomal subunits interlock around mRNA strand Step 3 second tRNA arrives at adjacent site of ribosome (its anticodon binds to 2nd mRNA codon) Step 4 1st amino acid detaches from its tRNA and binds to 2nd amino acid (peptide bond); ribosome moves down mRNA strand; 1st tRNA detaches Step 5 cycle repeated; ribosome moves along length of mRNA strand; forms chain of amino acids Step 6 chain elongates until reaches stop codon; components separate; process ends

49. The Cell Life Cycle • Introduction • Cell division = form of reproduction; produces daughter cells • Interphase • Majority of a cell’s life is spent in interphase • G0 phasespecialized cell functions (indefinite period of time) • G1 phase normal cell functions plus cell growth; duplication of organelles; protein synthesis (8+ hrs) • S Phase DNA replication (making copy of all DNA); 6-8 hrs • G2 phase protein sythesis occurs (2-5 hrs)

50. The Cell Life Cycle • M Phase (Mitosis)  1-3 hrs • Refers specifically to division and duplication of a cell’s nucleus • division of cytoplasm is called cytokinesis • Four stages of Mitosis • Prophase • Metaphase • Anaphase • Telophase