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Chapter 3: Cells – The Living Units

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1 Chapter 3: Cells – The Living Units

2 Cellular Basis of Life Robert Hooke – late 1600s – observed plant cells 1830s Schleiden & Schwann – concluded all living things are composed of cells Rudolf Virchow – found – all cells come from preexisting cells

3 1800s- Cell Theory Cell is the basic structural and functional unit of living organisms Activity of organism – depends on individual and collective activities of cells Principal of complementary structure and function – biochemical activities of cells are dictated by relative numbers of subcellular structures Continuity of life from one generation to another has a cellular basis

4 Human Body Trillions of cells 200 different cell types
Size ranges from 2 µm to 1 m Structural unit of all living things All cells composed of C, N, O, and other trace elements All cells have same basic parts (generalized or composite cell)

5 Human Cells All have 3 main parts Plasma membrane – outer boundary
Cytoplasm – intracellular fluid packed with organelles Nucleus – controls cellular activates

6 Plasma Membrane Also called the cell membrane Flexible
Defines the extent of cell Separates intracellular fluid from extracellular fluid

7 Fluid Mosaic Model Thin (7-10 nm) structure
Composed of double layer – bilayer of lipid molecules with protein molecules dispersed in it

8 Membrane Lipids Phospholipids –
Polar head – hydrophilic – “water loving” Non-polar tail – hydrophobic – “water fearing” Polar heads are attracted to water, lie on inner and out surfaces Sandwich like structure – heads on outside, tails on inside Majority of tails – unsaturated – have kinks and increase membrane fluidity

9 Membrane Lipids Glycoproteins - lipids with sugars attached
Only on outer membrane surface 5 % of total membrane Cholesterol – 20 % of total membrane Polar region hydroxyl group Nonpolar region – fused ring Stabilizes membrane Increases mobility of phospholipids Lipid Rafts – 20 % of outer membrane Assemblies of saturated phospholipids Packed tightly together Platforms for receptor molecules and cell signaling

10 Membrane Proteins Make up approximately 50 % of membrane
Responsible for specialized function 2 kinds of proteins Integral proteins Peripheral proteins

11 Membrane Proteins – Integral Protiens
Inserted into membrane Some stick out only on one side Others span entire membrane – transmembrane proteins Hydrophobic and hydrophilic regions Most involved in transport Form pores or channels Others – carriers – bind substances and move them into membrane Also receptors – relay messages to interior of cell

12 Membrane Proteins – Peripheral Proteins
Not embedded in membrane Attached loosely to integral proteins Include filaments that support membrane Some are enzymes Others – motor proteins – change cell shape during division and cell contraction Glycocaylx – “sugar coating” sugars attached to proteins Highly specific biological markers – allow cells to recognize each other

13 Membrane Junctions 3 factors that bind cells together
Glycoproteins in glycocaylx acts as adhesive Wavy contours of membrane of adjacent cells fit together – tongue and groove Specialized membrane junctions a. tight junction – integral proteins of adjacent cells fuse together, prevent molecules from passing b. desmosomes – anchoring junctions, mechanical couplings c. gap junctions – nexus cells connected by hallow cylinders – connections (transmembrane proteins), present in electrically excitable tissue


15 Membrane Transport Extracellular fluid – interstitial fluid
Rich, nutritious “soup” Amino acids, sugars, fatty acids, vitamins, hormones, salts, wastes, etc. Plasma Membrane – selectively permeable Allows some substances to pass, but NOT others Passive Processes – substances cross without energy input Active Process – substances need energy input to cross

16 Transport - Passive Diffusion – movement of molecules from an area of high concentration to an area of low concentration Down the concentration gradient Kinetic energy of molecules moves them Speed of diffusion – influenced by: size – smaller the molecules are the faster they move Molecules move until equilibrium is reached (no net movement) Plasma membrane – physical barrier – but molecule will diffuse if it is– Lipid soluble Small enough to pass through channels Assisted by carrier

17 Transport - Passive Simple Diffusion – nonpolar and lipid soluble substances diffuse directly though membrane Oxygen, carbon dioxide, fat-soluble vitamins, etc,

18 Transport - Passive Facilitated Diffusion – molecules that can not pass through the membrane by themselves Transported with the help of a protein Substance can binds the carrier protein in membrane Substance may also move through water filled channels Carriers – integral proteins – allow substances to pass through membrane Channels – transport proteins Transport water or ions through aqueous channels

19 Transport - Passive Osmosis – diffusion of solvent (water) through a selectively permeable membrane Aquaporins (APQs) water specific channels in the membrane Moves down the concentration gradient Also depends on the concentration of solutes Osmolarity – total concentration of all solute particles in a solution

20 Transport Passive Osmosis cont –
Water diffuses until hydrostatic pressure (back pressure exerted by water against the membrane) with in the cell is equal to its osmotic pressure (tendency of water to move into cell by osmosis) Tonicity – change in shape or tone of cells by altering internal water volume

21 Solutions Isotonic – cells with the same concentration of solutes on the inside and outside Hypertonic – solution has a higher concentration than the inside of the cell Water moves out, cells shrinks Hypotonic – solution is more dilute than inside of cell Water moves in, cell swells


23 Active Transport Processes
Active Transport – requires protein Combines specifically and reversibly with transported substances Solute pumps – move solutes against the concentration gradient Requires the input of energy Symbort System – 2 substances transported the same way (both inside or both outside) Antiport System – 2 substances transported opposite ways (one inside and the other outside)

24 Primary Active Transport
Hydrolysis of ATP  phosphorylation of transport protein Protein changes shape – pumps solute across membrane Ex. Na+-K+ pump – Na+K+ ATPase – drives sodium out of cell and potassium in

25 Secondary Active Transport
Single ATP powered pump indirectly drives secondary active transport Na moves back into cell, another substance is cotransported with it Ex. Sugar, amino acids, ions, etc

26 Vesicular Transport Fluids containing large particles and macromolecules are transported in membranous sacs – vesicles Exocytosis – process that ejects substances from interior of cell

27 Vesicular Transport Endocytosis – process that moves substances into the cell Substances moved in by the infolding of the membrane – coated pit – clathrin – protein coating, then vesicle detaches Phagocytosis – cells engulfs large solid material Bacteria, debris, etc Endocytic vesicle – phagosome Amoeboid motion – flowing of cytoplasm into temporary pseudopods Pinocytosis – fluid phase endocytosis Plasma membrane surrounds small volume of fluid containing dissolved material Receptor mediated endocytosis – plasma membrane binds only certain substances

28 Vesicular Transport Other protein coats –
Caleolae – tubular or flask shaped inpocketings of plasma membrane Coatomer (COP1 & COP2) proteins – vesicular trafficking Transport substances between organelles

29 Plasma Membrane – Membrane Potential
Membrane Potential – voltage – electrical potential energy resulting from separation of oppositely charged particles

30 Plasma Membrane – Membrane Potential
Resting State – resting membrane potential – range mV Cell said to be polarized (-) indicates inside is negative compared to the outside Diffusion – causes ionic imbalances that polarize the membrane, active transport maintains membrane polarization Ions – K+ and protein – inside cell Na+ and Cl- outside cell Membrane somewhat permeable to K+ - leaky channels Protein anions cannot follow

31 Plasma Membrane – Membrane Potential
Membrane becomes negative = -90 mV Na+ also a factor – attracted to cell interior – bring membrane to -70 mV Active transport – depends on diffusion More Na+ in, the more is pumped out Na+/K+ pump – 3 Na out for 2 K in Electrochemical gradient – electrical and concentration (chemical) forces

32 Cell-Environment Interactions
Cell Adhesion Molecules (CAMs) Key role in embryonic development, wound repair, and immunity Sticky glycoproteins

33 Cell-Environment Interactions
Functions – Molecular “Velcro” cells use to anchor themselves to molecules in extracellular space and to each other The “arms: that migrating cells use to haul themselves past one another SOS signals – sticking out from blood vessels lining that rally WBC to infected or damaged area Mechanical sensors – respond to tension at cell surface by stimulating synthesis or degradation of adhesive membrane junction Transmitters of intracellular signals that direct cell migration, proliferation, and specialization

34 Roles Membrane receptors – integral proteins and glycoproteins that serve as binding sites Cell Signaling – coming together and touching of cells Cells recognize each other Essential for normal development and immunity

35 Roles 2. Chemical Signaling –
Ligands – signaling chemicals, bind to specific plasma membrane receptors Include – neurotransmitters, hormones, paracrines G-Protein – linked receptors – exert effects through G-protein Second messengers are generated and connect plasma membrane events to internal Ex. Cyclic AMP – Ca2+ Activates a protein kinase cascade Nitric oxide (NO) – another messenger – important signaling molecule

36 Cytoplasm “cell forming’ material
Cell material between the plasma membrane and the nucleus 3 major elements – cytosol, organelles, and inclusions

37 Cytoplasm 1. Cytosol Viscous semitransparent fluid
Colloid and solution properties Dissolved (in water) – protein, sugar, salts, and solutes 2. Organelles - Carry out specific functions – synthesize proteins, package proteins, etc. Chemical substances not always present 3. Inclusions - Stored nutrients, lipid droplets, pigment, water containing vacuoles, crystals of various types

38 Organelles “little organs” Nonmembranous – lack membranes
Membranous – with membranes

39 Mitochondria Lozenge-shaped membranous organelles
Power plants of cells 2 membranes – Outer – smooth and featureless Inner – folds inward forming cristae Gel-like substance inside Food particles – glucose – broken down into water and carbon dioxide by enzymes Metabolites broken down and oxidized – energy released and captured Aerobic cellular respiration

40 Mitochondria Contain their own DNA, RNA, and ribosomes
Can reproduce themselves 37 genes – direct synthesis of 1% of proteins needed Similar to bacteria (purple bacteria phylum) Believed to have arose from bacteria that evaded plant and animal cells

41 Ribosomes Small dark staining granules
Protein and a variety of RNA – ribosomal RNA Site of protein synthesis Some float freely Others attached to rough ER Free ribosomes – make soluble proteins Rough ER – make proteins destined for cell membranes or export

42 Endoplasmic Reticulum (ER)
“network” with in cytoplasm Intracellular connected tubes and parallel membranes enclosed fluid filled cavities or cisternae Continuous with the nuclear membrane Half of cells total membrane 2 types – smooth and rough

43 Rough Endoplasmic Reticulum (RER)
Surface covered with ribosomes Proteins from ribosomes – enter and are modified “Membrane factory”

44 Smooth Endoplasmic Reticulum (SER)
Continuous with the rough ER No role in protein synthesis Involved in: Lipid metabolism, cholesterol synthesis, synthesis of lipid components – of lipoproteins Synthesis of steroid hormones (sex hormones) Absorption, synthesis, and transport of fats Detox of drugs, pesticides, and carcinogens Breakdown of stored glycogen into free glucose - Muscle – also stores calcium

45 Golgi Apparatus Stacked and flattened membranous sacs
Traffic director for cellular proteins Modify, concentrate and package proteins and lipids Secretory vesicles or granules migrated to plasma membrane and discharge contents

46 Lysosomes Inactive digestive enzymes Cells demolition crew
Digest particles taken in by endocytosis, particularly bacteria, viruses, toxins Degrade worn-out or nonfunctional organelles Metabolic functions – glycogen breakdown and release Breakdown of nonuseful tissues – uterine lining during menstruation Breaking down of bone to release calcium into blood - Autolysis – lysosome rupture and cell digests itself

47 Endomembrane System System of organelles that work together to:
Produce, store, and export biological materials Degrade potential harmful substances ER, Golgi, secretory vessels, and lysozomes, also nuclear membrane

48 Peroxisomes “peroxide bodies”
Membranous sacs with a variety of powerful enzymes Oxidases and catalyzes Oxidase – use molecular oxygen to detoxify harmful substances – alcohol/fermaldehyde Neutralize dangerous free radicals – highly reactive chemicals with unpaired electrons Convert to hydrogen peroxide Numerous in liver and kidney

49 Cytoskeleton “cell skeleton”
Elaborate network of rods running through cytosol 3 parts – microfilaments, intermediate filaments, and microtubules

50 Cytoskeleton - Microtubules
Elements with largest diameter Hallow tubes made of spherical protein subunits- tubulins Organelles attached Motor proteins – move and reposition organelles

51 Cytoskeleton - Microfilaments
Thinnest elements of cytoskeleton Strands of protein – actin Act together with myosin to generate contractile forces

52 Cytoskeleton – Intermediate Filaments
Though insoluble protein fibers Woven ropes Internal wires to resist pulling forces acting on cell

53 Centrosome and Centrioles
Centrosome – cell center, microtubule organizing center Centrioles – small barrel shaped organelles oriented at right angles to each other

54 Cellular Extensions Cilia – whip like motile cellular extensions on cell surface Move substances in one direction across cell surface Flagella – long projection Ex. Sperm cell – commonly only a tail Bases – basal bodies – pattern of microtubules Micorvilli – minute, fingerlike extensions of plasma membrane, increase the SA of plasma membrane

55 Nucleus Control center Genes All body cells have nucleus
RBC eject their nucleus – anucleate Average – 5 µm Largest organelle 3 regions – nuclear envelope, nucleoli, and chromatin

56 Nuclear Envelope Double membrane bilayer
Outer membrane continuous with ER Inner membrane lined by nuclear lamina Nuclear pores – protein (NPC) – aqueous transport channel – entry and exist Selectively permeable membrane Nucleoplasm – jellylike fluid on inside

57 Nucleoli Dark-staining spherical bodies with in the nucleus
Typically 1 or 2 but maybe more Sites where ribosomal subunits are assembled Associated with the nucleolar organizer regions – genetic information for synthesizing rRNA rRNA – combined with proton = ribosome

58 Chromatin Fine, unevenly stained network (microscope)
Really bumpy threads Composed of 30: DNA, 60% histone proteins, 10% RNA chains Fundamental unit – nucleosomes – cluster of 8 histone proteins connected by DNA Pack DNA Ready to divide – condense into chromosomes

59 Cell Life Cycle Series of changes a cell goes through 2 major periods
Interphase Cell Division

60 Interphase Period from cell formation to cell division Subphases:
G1 (gap 1) phase – Cell metabolically active Synthesizes protein and grows S phase – DNA replicated New histones made and assembled into Chromatin G2 (gap 2) phase – brief Enzymes and proteins needed for division are synthesized

61 Interphase – DNA Replication
DNA helix unwinds Helicase enzyme untwists helix, replication fork – Y-shaped separation Each strand serves as a template DNA Polymerase – attaches complementary nucleotides, leading strand and lagging strand DNA ligase hooks segments of lagging strand together, leading strand - continuous

62 Cell Division M (mitotic) phase 2 events – mitosis and cytokinesis
Mitosis – division of the nucleus 4 phases Prophase Metaphase Anaphase Telophase

63 Cell Division Cytokinesis – division of the cytoplasm
Begins in late anaphase Plasma membrane drawn inward (cleavage furrow) by contractile ring 2 cells pinched apart

64 Control of Cell Cycle Signals for cell division Ratio of SA to volume
64 fold increase in volume, only 16 fold increase in SA Inadequate SA for nutrient and waste exchange 2. Chemical Signals – growth factors, hormones, etc.

65 Control of Cell Cycle Cyclins and Cdks (cyclin dependent kinases)
Proteins and enzymes that signal the cell to divide Also checkpoints for cell division – MPF – M-phase promoting factor – OK – signal to pass G2 and enter M

66 Protein Synthesis DNA – blueprint for proteins
Gene - sequence of DNA that carries instructions for proteins DNA bases – A, C, T, G 3 bas segments – triplet – “word” that specifies an amino acid Most genes have exons – which code for amino acids separated by introns – noncoding segments of DNA Introns – can range from 60100,000 nucleotides long “junk DNA” – must be cut out to make a protein

67 Protein Synthesis DNA can not leave the nucleus so need a carrier
RNA – (carrier) 3 types Messenger RNA (mRNA) – long nucleotide strand, “half DNA” codes for a protein Ribosomal RNA (rRNA) – part of ribosome Transfer RNA (tRNA) – small roughly L-shaped molecules

68 Protein Synthesis 2 Parts Transcription – DNA  mRNA
initiation, elongation and termination Promoter – start point RNA polymerase – initiates transcription, pulls strands apart, aligns RNA nucleotides Termination signal – transcription ends – mRNA pulls off

69 Protein Synthesis mRNA – must then be modified – splicosomes – cut introns (junk) and splice (glue together) remaining exons

70 Protein Synthesis 2. Translation –
base sequence (mRNA)  converted to amino acids (protein) Codon – 3 bas sequence on mRNA – 64 codons for 20 amino acids Anticodon - 3 base sequence on tRNA – brings in amino acid Amino acids hook together – form a chain = PROTEIN

71 DNA – other roles Antisense RNA – can intercept and bind to protein coding mRNA, prevent it from being translated into protein microRNAs – small RNAs that can interfere and suppress mRNA Ribositches – folded mRNA, code for a protein Can turn on protein synthesis in response to changes in the environment

72 Protein Degradation Proteins - no longer useful
Ubiquitins – proteins that attach to old/bad protein – mark it for destruction Proteasomes – digest the protein

73 OUTSIDE _ Extracellular Materials
Body fluids – interstitial fluid, blood plasma, cerebrospinal fluid Cellular secretions – substances that aid in digestion and act as lubricants Extracellular Matrix – jelly-like, composed of proteins and polysaccharides “cell glue” holds cells together

74 Development Embryo –cells – chemical signals that direct pathways of development Cell differentiation – development of specific and distinctive features of cells Apoptosis -programmed cell death Hyperplasia – accelerated growth Atrophy – decrease in size of organ or body tissue

75 Development Aging – Telomere – string of nucleotides at the end of a chromosome that protect it from fraying Get shorter with each cell division Aging – shorten, not protected Telomerase – enzyme that protects from degradation Found in egg and sperm cells, NOT in normal body cells “fountain of youth”

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