Cell Structure and Function

1. Cell Structure and Function Anatomy & Physiology I Chapter 3

2. Modern Cell Theory • All organisms composed of cells and cell products. • The cell is the smallest structural and functional unit of life. • An organism’s structure and functions are due to the activities of its cells. • Cells come only from preexisting cells, not from nonliving matter. • Cells of all species have many fundamental similarities in their chemical composition and metabolic mechanisms.

3. Cell Diversity • Over 200 different types of human cells • Types differ in size, shape, subcellular components, and functions

4. Cell Shapes • Squamous - thin and flat with nucleus creating bulge • Polygonal - irregularly angular shapes with 4 or more sides • Stellate – starlike shape • Cuboidal – squarish and about as tall as they are wide • Columnar - taller than wide • Spheroid to Ovoid – round to oval • Discoid - disc-shaped • Fusiform - thick in middle, tapered toward the ends • Fibrous – threadlike shape

5. Cell Shapes Squamous Cuboidal Columnar Polygonal Stellate Spheroid Discoid Fusiform (spindle-shaped) Fibrous

6. Erythrocytes Fibroblasts Epithelial cells (a) Cells that connect body parts, form linings, or transport gases Nerve cell Skeletal Muscle cell (e) Cell that gathers information and control body functions Smooth muscle cells (b) Cells that move organs and body parts Sperm Macrophage (f) Cell of reproduction Fat cell (c) Cell that storesnutrients (d) Cell that fights disease

7. Generalized Cell • All cells have some common structures and functions • Human cells have three basic parts: • Plasma membrane—flexible outer boundary • Cytoplasm—intracellular fluid containing organelles • Nucleus—control center

8. Generalized Animal Cell ZOOMING IN • What is attached to the ER to make it look rough? • What is the liquid part of the cytoplasm called?

9. Plasma Membrane • Regulates the movement of substance into and out of the cell • Encloses cell contents • Separates intracellular fluid (ICF) from extracellular fluid (ECF) • Interstitial fluid (IF) = ECF that surrounds cells • Participates in cellular activities • Bilayer structure • Phospholipids • Cholesterol • Proteins

10. Membrane Lipids • 75% phospholipids (lipid bilayer) • Phosphate heads: polar and hydrophilic • Fatty acid tails: nonpolar and hydrophobic • 5% glycolipids • contributes to glycocalyx – carbohydrate coating on thecells surface • 20% cholesterol • Increases membrane stability and fluidity

11. Plasma Membrane ZOOMING IN • How many layers make up the main substance of the plasma membrane?

12. Membrane Protein Functions Breakdown products Chemical messenger Ions CAM of another cell (c) Ion Channel A channel protein that is constantly open and allows ions to pass into and out of the cell (a) Receptor A receptor that binds to chemical messengers such as hormones sent by other cells (b) Enzyme An enzyme that breaks down a chemical messenger and terminates its effect (d) Gated ion channel A gated channel that opens and closes to allow ions through only at certain times (e) Cell-identity marker A glycoprotein acting as a cell- identity marker distinguishing the body’s own cells from foreign cells (f) Cell-adhesion molecule (CAM) A cell-adhesion molecule (CAM) that binds one cell to another

13. Glycocalyx • Unique fuzzy coat external to the plasma membrane • carbohydrate moieties of membrane glycoproteins and glycolipids • unique in everyone, but identical twins • Functions • protection - cell adhesion • immunity to infection - fertilization • defense against cancer - embryonic development • transplant compatibility

14. Surface Organelles Structures projecting from the cell surface used for motion • Cilia • Flagellum

15. Structure of Cilia Cilia 10 m

16. Cilia • Motile cilia – respiratory tract, uterine tubes, ventricles of the brain, efferent ductules of testes • beat in waves • sweep substances across surface in same direction • power strokes followed by recovery strokes Mucus Saline layer Epithelial cells 1 2 3 4 5 6 7 Power stroke Recovery stroke

17. Cilia & Cystic Fibrosis • Saline layer at cell surface due to chloride pumps move Cl- out of cell. Na+ ions and H2O follow • Cystic fibrosis – hereditary disease in which cells make chloride pumps, but fail to install them in the plasma membrane • chloride pumps fail to create adequate saline layer on cell surface • thick mucus plugs pancreatic ducts and respiratory tract • inadequate digestion of nutrients and absorption of oxygen • chronic respiratory infections • life expectancy of 30 Mucus Saline layer Epithelial cells

18. Flagella • tail of the sperm - only functional flagellum • whiplike structure • much longer than cilium • movement is more snakelike • no power stroke or recovery stroke as in cilia

19. Cytoplasm • Located between plasma membrane and nucleus • Cytosol • Water with solutes (protein, salts, sugars, etc.) • Cytoplasmic organelles • Metabolic machinery of cell • Inclusions • Granules of glycogen or pigments, lipid droplets, vacuoles, and crystals

20. Cytoplasmic Organelles • Nucleus - Contains chromosomes (DNA) and nucleolus • Rough ER - Manufactures all secreted proteins • Smooth ER – Synthesize steroids and other lipids; manufactures all membranes of the cell • Ribosomes - Site of protein synthesis • Mitochondria – cellular respiration (ATP production) • Golgi apparatus – Storage warehouses of the cell; carbohydrate synthesis • Lysosomes - contain digestive enzymes; Digest ingested bacteria, viruses, and toxins • Peroxisomes - Detoxify harmful or toxic substances; Neutralize dangerous free radicals • Centrioles - play role in cell division

21. Nucleus Largest organelle in a cell • Genetic library with blueprints for nearly all cellular proteins • Responds to signals and dictates kinds and amounts of proteins to be synthesized • Most cells are uninucleate • Red blood cells are anucleate • Skeletal muscle cells, bone destruction cells, and some liver cells are multinucleate

22. Nuclear pores Nuclear envelope Nucleus Chromatin (condensed) Nucleolus Cisternae of rough ER

23. Nucleic Acids – DNA and RNA DNA and RNA have similar structures • Four nucleotides • Adenine (A) • Guanine (G) • Cytosine (C) • Thymine (T) or uracil (U) • Sugar • Ribose or deoxyribose • Phosphate • Nitrogen base

24. DNA Molecular Structure Adenine • DNA – deoxyribonucleic acid - a long threadlike molecule with uniform diameter, but varied length • 46 DNA molecules in the nucleus of most human cells • DNA and other nucleic acids are polymers of nucleotides • Each nucleotide consists of • one sugar - deoxyribose • one phosphate group • one nitrogenous base • A, T, G or C NH 2 C N N C H C C H C N N H O O H O P O CH 2 O H H H H H O H H Phosphate Deoxyribose

25. DNA Structure • Molecular shape is a double helix (resembles a spiral staircase) • each sidepiece is a backbone composed of phosphate groups alternating with the sugar deoxyribose. • steplike connections between the backbones are pairs of nitrogen bases A T G C A T A T G C A T C G T A G C T A C G T A C G Sugar–phosphate backbone Sugar–phosphate backbone

26. Complementary Base Pairing • Nitrogenous bases united by hydrogen bonds • a purine on one backbone with a pyrimidine on the other • A – T two hydrogen bonds • C – G three hydrogen bonds • DNA base pairing • A – T • C – G • Law of Complementary Base Pairing • one strand determines base sequence of other G C T T A A C G T A C G Sugar–phosphatebackbone Sugar–phosphatebackbone

27. DNA Function • Genes – genetic instructions for synthesis of proteins • Gene – segment of DNA that codes for a specific protein • Genome - all the genes of one person • humans have estimated 25,000 to 35,000 genes • 2% of total DNA • other 98% is noncoding DNA • plays role in chromosome structure • regulation of gene activity • no function at all – “junk” DNA

28. Chromatin and Chromosomes 1 DNA double helix 2 nm • chromatin – fine filamentous DNA material complexed with proteins • occurs as 46 long filaments called chromosomes • in nondividing cells, chromatin is so slender it cannot be seen with light microscope • histones – disc-shaped cluster of eight proteins • DNA molecule winds around the cluster • appears to be divided into segments - nucleosomes • nucleosome consists of : • core particle – histones with DNA around them • linker DNA – short segment of DNA connecting core particles Core particle Linker DN A 2 DNA winds around core particles to form nucleosomes 11 nm in diameter 1 1 nm Nucleosome Nucleosomes fold accordion- like into zigzag fiber 30 nm in diameter 3 30 nm 30 nm fiber is thrown into irregular loops to form a fiber 300 nm thick 4 300 nm In dividing cells only In dividing cells, looped chromatin coils further into a 700 nm fiber to form each chromatid 5 700 nm Chromatids Centromere 6 700 nm Chromosome at the midpoint (metaphase) of cell division

29. RNA: Structure and Function • RNA much smaller cousin of DNA (fewer bases) • messenger RNA (mRNA) over 10,000 bases • ribosomal RNA (rRNA) • transfer RNA (tRNA) 70 - 90 bases • DNA averages 100 million base pairs • one nucleotide chain (not a double helix as DNA) • ribose replaces deoxyribose as the sugar • uracil replaces thymine as a nitrogenous base • Essential function • interprets code in DNA • uses those instructions for protein synthesis • leaves nucleus and functions in cytoplasm

30. What is a Gene? • A segment of DNA that carries the code for a particular protein • The segment of DNA first codes for the production of a molecule of RNA • The molecule of RNA then plays a role in synthesizing one or more proteins (protein synthesis) • The amino acid sequence of a protein is determined by the nucleotide sequence in the DNA

31. Human Genome • Genome – all the DNA in one 23-chromosome set • 3.1 billion nucleotide pairs in human genome • 46 human chromosomes comes in two sets of 23 chromosomes • one set of 23 chromosomes came form each parent • each pair of chromosomes has same genes but different versions (alleles) exist

32. Genetic Code • body can make millions of different proteins, all from the same 20 amino acids, and encoded by genes made of just 4 nucleotides (A,T,C,G) • Genetic code – a system that enables these 4 nucleotides to code for the amino acid sequence of all proteins • minimum code to symbolize 20 amino acids is 3 nucleotides per amino acid • Base triplet – a sequence of 3 DNA nucleotides that stands for one amino acid • codon - the 3 base sequence in mRNA • 64 possible codons available to represent the 20 amino acids • 61 code for amino acids • Stop Codons – UAG, UGA, and UAA – signal the ‘end of the message’, like a period at the end of a sentence • Start Codon – AUG codes for methionine , and begins the amino acid sequence of the protein

33. Summary of Protein Synthesis • process of protein synthesis • DNA mRNA protein • transcription – step from DNA to mRNA • occurs in the nucleus where DNA is located • translation – step from mRNA to protein • most occurs in cytoplasm • 15-20% of proteins are synthesized in the nucleus

34. Transcription • DNA too large to leave nucleus and participate directly in cytoplasmic protein synthesis • necessary to make a small mRNA copy that can migrate through a nuclear pore into the cytoplasm • Transcription – copying genetic instructions from DNA to RNA

35. Translation • translation – the process that converts the language of nucleotides into the language of amino acids • ribosomes - translate sequence of nucleotides into the sequence of amino acids • occur mainly in cytosol, on surface of rough ER, and nuclear envelope

36. Nuclear envelope DNA Transcription RNA Processing Pre-mRNA mRNA Nuclear pores Ribosome Translation Polypeptide

37. Review of Protein Synthesis 1 DNA double helix Seven base triplets on the template strand of DNA 2 The corresponding codons of mRNA transcribed from the DNA triplets 3 The anticodons of tRNA that bind to the mRNA codons 4 The amino acids carried by those six tRNA molecules 5 The amino acids linked into a peptide chain 6

38. Alternative Splicing of mRNA • One gene can code for more than one protein Gene (DNA) 1 T ranscription Intron Exon Pre-mRN A A B C D E F 2 Splicing mRN A 1 mRN A 2 mRN A 3 A C D B D E A E F 3 T ranslation Protein 1 Protein 2 Protein 3

39. Cell Cycle • Defines changes from formation of the cell until it reproduces • Includes: • Interphase • Cell division (mitotic phase)

40. Interphase • Period from cell formation to cell division • Nuclear material called chromatin • Subphases: • G1 (gap 1)—vigorous growth and metabolism • S (synthetic)—DNA replication • G2 (gap 2)—preparation for division

41. Cell Cycle S Growth and DNA synthesis G2 Growth and final preparations for division G1 Growth M

42. Cell Division • Mitotic (M) phase of the cell cycle • Essential for body growth, tissue repair and renewal • Does not occur in most mature cells of nervous tissue, skeletal muscle, and cardiac muscle

43. Cell Division Includes two distinct events: • Mitosis—four stages of nuclear division: • Prophase - Chromosomes become visible • Metaphase - chromosomes are aligned at the equator • Anaphase - Centromeres of chromosomes split simultaneously—each chromatid now becomes a chromosome • Telophase - chromosomes uncoil to form chromatin • Cytokinesis—division of cytoplasm by cleavage furrow

44. The stages of mitosis. ZOOMING IN • If the original cell shown has 46 chromosomes, how many chromosomes will each new daughter cell have?

45. Membrane Transport • plasma membrane – a barrier and a gateway between the cytoplasm and ECF • selectively permeable – allows some things through, and prevents other things from entering and leaving the cell • Some molecules easily pass through the membrane; others do not • Travel across the membrane is based on several factors: • Molecular size • Solubility • Electrical charge

46. Membrane Permeability • Diffusion through lipid bilayer • Nonpolar, hydrophobic, lipid-soluble substances diffuse through lipid layer • Diffusion through channel proteins • water and charged, hydrophilic solutes diffuse through channel proteins in membrane • Cells control permeability by regulating number of channel proteins or by opening and closing gates

47. Movements Not Requiring Cellular Energy Passive transport mechanisms • Simple Diffusion • Facilitated Diffusion • Carrier-mediated facilitated diffusion • Channel-mediated facilitated diffusion • Osmosis • Filtration Passive transport mechanisms require no ATP. Random molecular motion of particles provides the necessary energy.

48. Movements Requiring Cellular Energy Active transport • Carrier-mediated Active Transport • Vesicular (Bulk) Transport • Endocytosis • Phagocytosis • Pinocytosis • Exocytosis Active transport mechanisms consume ATP.

49. Simple Diffusion • Simple Diffusion – the net movement of particles from area of high concentration to area of low concentration • due to their constant, spontaneous motion • Also known as movement down the concentration gradient – concentration of a substance differs from one point to another Downgradient Upgradient

50. Simple Diffusion Extracellular fluid Lipid- soluble solutes Simple diffusion of fat-soluble molecules directly through the phospholipid bilayer Cytoplasm