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2 3.1 Cellular Organization

3 A.Introduction 1.Three main parts of a cell a.Plasma membrane – surrounds the cell, keeps it intact, and regulates passage into and out of the cell b.Nucleus – control center c.Cytoplasm – gelatinous, semi-fluid of water and suspended and dissolved substances

4 Introduction, cont 2.Organelles (little organs) are scattered throughout the cytoplasm and have various functions 3.The cytoskeleton maintains cell shape and allows the cell and its content to move

5 A typical animal cell

6 B.Plasma Membrane 1.Separates the inside of the cell (cytoplasm) from the outside 2.Fluid-mosaic model a.Phospholipid bilayer – hydrophilic heads point outward and hydrophobic tails point inward b.Attached peripheral and integral proteins serve as receptors, channels, and carriers c.Cholesterol molecules stabilize the membrane d.Glycoproteins and glycolipids attached to outer surface of some protein and lipid molecules, mark cells as belonging to a particular individual

7 Fluid-mosaic model of the plasma membrane

8 C.The Nucleus 1.Stores genetic information 2.Chromatin a.Contains DNA, protein, and some RNA b.Coils into rod-like structures called chromosomes before the cell divides c.Immersed in nucleoplasm 3.Nucleoli a.Dark-staining bodies containing rRNA and protein b.Site where ribosomes are formed

9 The Nucleus, cont 4.Nuclear envelope separates nucleus from cytoplasm a.Lipid bilayer with many nuclear pores b.Outer layer is continuous with the endoplasmic reticulum

10 The Nucleus

11 D.Ribosomes 1.Composed of two subunits containing protein and rRNA 2.Can be found free within the cytoplasm, singly or in groups called polyribosomes; produce proteins that are used inside the cell 3.Also found attached to the endoplasmic reticulum; produce proteins that may be secreted by the cell

12 E.Endomembrane System 1.Nuclear envelope 2.Endoplasmic reticulum (ER) a.Continuous with the outer membrane of the nuclear envelope, it is a system of membranous channels and saccules b.Rough ER 1)Has attached ribosomes 2)Processes proteins produced by attached ribosomes

13 Endomembrane system, cont c.Smooth ER 1)Has no attached ribosomes 2)Synthesizes phospholipids, detoxifies drugs, and has other functions depending on the type of cell

14 Endoplasmic Reticulum

15 Endomembrane System, cont 3.Golgi apparatus a.Stacks of curved saccules b.Processes, packages, and secretes various substances c.Receives protein and/or lipid-filled vesicles from ER d.Contains enzymes that modify proteins and lipids e.Vesicles leave the Golgi apparatus and move to other parts of the cell or to the plasma membrane for secretion f.Produces lysosomes

16 Endomembrane System Function

17 Endomembrane system, cont 4.Lysosomes a.Contain hydrolytic digestive enzymes; nick-names “suicide sacs” b.Autodigestion responsible for cell rejuvenation and development and removal of worn-out organelles c.Can fuse with vesicles of material brought into the cell for destruction d.Tay-Sach’s disease – metabolic disorder involving missing or inactive lysosomal enzymes in nerve cells

18 F.Peroxisomes and Vacuoles 1.Peroxisomes a.Enzyme-containing vesicles, similar to lysosomes b.Detoxify drugs, alcohol, and other toxins c.Large numbers found in liver and kidney d.Break down fatty acids from fats 2.Vacuoles isolate substances captured inside the cell

19 G.Mitochondria 1.Rod-shaped organelle bound by a double membrane 2.Inner membrane folds into cristae to increase surface area 3.Site of ATP production through cellular respiration – cell powerhouse

20 Mitochondrion Structure

21 H.The cytoskeleton 1.Microtubules - help maintain the cell’s shape and anchors or assists the movement of organelles 2.Intermediate filaments – involved in cell to cell junctions 3.Actin filaments – involved in cell movement 4.Assembly regulated by the centrosome

22 I.Centrioles 1.Composed of microtubules with a pattern 2.A pair of perpendicular centrioles are found near the nucleus of every cell 3.In a area called the centrosome 4.Involved in cell division by forming the mitotic spindle 5.Form the basal body (anchor point) for each cilium or flagellum

23 Structure of basal bodies and flagella

24 J.Cilia and flagellum 1.Cilia are hair-like projections from the free surface of a cell; beat in unison to move material along the cell surface 2.Flagellum – a single whip-like extension for cell movement; sperm is the only human cell with a flagellum

25 Cilia and flagella

26 Structures in Human Cells

Crossing the Plasma Membrane

28 A.Introduction 1.The plasma membrane is selectively (semi) permeable – only certain ions and molecules can cross through 2.Passive processes – does NOT require cellular energy (ATP) 3.Active processes – DOES require cellular energy

29 B.Simple Diffusion 1.Movement of atoms or molecules from an area of higher concentration to an area of lower concentration (down a concentration gradient) 2.Movement of atoms or molecules occur until they are equally distributed 3.No cellular energy is required (passive) 4.Small lipid-soluble molecules will diffuse through the lipid portion of the membrane; includes blood gases

30 Diffusion

31 C.Osmosis 1.Diffusion of water across a plasma membrane 2.Occurs when there is an unequal distribution of water on either side of a selectively permeable membrane; water passes freely but solutes do not 3.Osmotic pressure – force exerted on a selectively permeable membrane

32 Osmosis, cont 4.Tonicity – concentration of solute versus the concentration of water a.Isotonic – equal concentration of solutes (dissolved substances) and solvent (water) inside and outside cell; cell shape is maintained b.Hypotonic – higher concentration of water (lower concentration of solutes) outside cell; water moves into cell causing it to swell and eventually lyse c.Hypertonic – lower concentration of water (higher concentration of solutes) outside cell; water moves out of cell causing it to shrink or crenate

33 Tonicity

34 D.Filtration 1.Filtration is the movement of liquid from high pressure to low pressure 2.Blood pressure creates the hydrostatic pressure in capillaries where filtration occurs

35 E.Transport by carriers 1.Facilitated diffusion a.Solutes are transported by means of a protein carrier b.Movement from area of higher concentration to area of lower concentration c.No energy required - passive

36 Transport by carriers, cont 2.Active transport a.Solutes move up their concentration gradient (low concentration area to high concentration area) b.Requires a protein carrier (often called pumps) c.Requires the use of cellular energy d.The sodium/potassium pump (Na + /K + pump) is an important pump that all cells have

37 Active Transport

38 F.Endocytosis and Exocytosis 1.In endocytosis (bring into the cell) the plasma membrane envelopes a substance and forms an intracellular vesicle a.Phagocytosis (“cell eating”) – cell ingests solid particles b.Pinocytosis (“cell drinking”) – cell consumes solutions 2.In exocytosis (takes out of the cell) a vesicle fuses with the plasma membrane as secretion occurs

39 Crossing the Plasma Membrane

The Cell Cycle

41 A.Introduction 1.Set of stages that take place between the time a cell divides and the time the daughter cell divides 2.Controlled by external and internal signals 3.Apoptosis (cell death) occurs at a restriction checkpoint if the cell did not complete mitosis and is abnormal 4.Some specialized cells no longer go through the cell cycle - muscle cells and nerve cells

42 B.Cell Cycle Stages - Interphase 1.Cell is not dividing, but is preparing to divide 2.The cell carries on regular activities 3.Three phases a.G 1 phase – cell doubles number of organelles and accumulates materials used for DNA synthesis b.S phase – “synthesis” phase; DNA replication occurs c.G 2 phase – cell synthesizes proteins that will assist cell division and completes replication of centrioles

43 The Cell Cycle

44 C.Major events during interphase 1. Replication of DNA a.Before replication, the two strands of DNA are hydrogen bonded together b.Parental DNA strands unwind (hydrogen bonds are broken) c.New complimentary nucleotides pair with nucleotides in the parental DNA strands and DNA polymerase joins the new nucleotides d.When replication is complete, two identical double helix molecules have been formed e.Each strand of this double helix is equivalent to a chromatid; held together by the centromere

45 Overview of DNA Replication

46 Ladder configuration & DNA replication

47 2.Protein synthesis a.DNA also serves as a template for RNA formation and protein construction b.Two steps involved in protein synthesis are: 1)Transcription – formation of mRNA 2)Translation – involves mRNA, tRNA, and rRNA; specifies the order of amino acids in a polypeptide

48 Protein Synthesis Process

49 D.The Cell Cycle – Mitotic Stage 1. M-stage – nuclear division stage divided into 4 phases a.Prophase 1)The centrioles near nucleus begin moving towards opposite ends of nucleus 2)Spindle fibers appear between the centrioles 3)Nuclear envelope begins to fragment 4)Nucleolus begins to disappear 5)Chromosomes appear randomly and attached to spindle fibers by their centromere

50 M-stage, cont b.Metaphase 1)Spindle is fully formed 2)Chromosomes are aligned at the equator c.Anaphase 1)Centromere splits 2)Sister chromatids separate (now called chromosomes) 3)Chromosomes move toward opposite poles of the spindle (toward centrioles) 4)Some spindle fibers push the chromosomes apart while others pull them toward the poles

51 M-stage, cont d.Telophase 1)Chromosomes become chromatin 2)Spindle disappears and nucleoli appear 3)Nuclear envelope reassembles and two daughter cell nuclei can be observed

52 2.The Cell Cycle - Cytokinesis a.Cytokinesis – division of the cytoplasm and organelles b.Begins in anaphase and completes in telophase c.Actin filaments form a ring around the equator that contracts, pinching the cell in half

53 Mitotic Stage of the Cell Cycle

54 Mitosis in a whitefish embryo

55 3.Importance of mitosis a.Maintains chromosome number b.Each cell in our body is genetically identical c.Each cell type has certain genes turned on and others turned off to give the different types of body cells d.Important to the growth and repair of multicellular organisms

56 E.Meiosis 1.Known as reduction division because the chromosome number is cut in half 2.The four phase of mitosis are repeated twice with some changes in the steps that occur 3.The gametes (ova and sperm) have half the chromosomes of normal body cells so that when they join to form the zygote, the chromosome number is correct for that organism.