Cell Form and Function

1. Cell Form and Function Dr. Anderson GCIT

2. Cell Diversity • Connect tissues and transportation – blood, epithelia • Body movement – muscles (smooth, striated, cardiac) • Storage – adipose (fat cells), hepatocytes • Immune Function – WBC’s • Communication and information processing – nerve cells • Reproduction – Egg and sperm cells

3. Cell Membrane • Keeps the cell contents separate from the environment (extracellular fluid)

4. The Fluid Mosaic Model • Cell membrane is made of a phospholipid bilayer • Self-assembling! • Extremely thin

5. Outside of cell – interstitial fluid Polar Heads Non-polar tails Polar Heads Inside of cell – cytoplasm Polar Heads are phospholipids and the non-polar (hydrophobic) ends are fatty acids

6. Membrane Proteins Facilitate the transport of material across the membrane Integral (trans-membrane) protein – facilitates transport into and out of the cell

7. Membrane Proteins • Peripheral protein – can be attached to inside or outside layer of cell membrane • Act as enzymes (outside and inside) or serve to move or support the cell (inside)

8. Glycoproteins – sugar-bound proteins Glycoproteins – make up a sugary coat that envelops the cells called the glyco-calyx or “sugar cup”

9. The Glycocalyx • The carbohydrates on the cell surface provide a way for some cells to recognize each other • Sperm and egg • WBC and bacteria or other pathogens

10. Membrane Junctions • Bind cells together – glycoproteins act as adhesive • Cell membrane structure – tongue-and-groove • Specialized Junctions – • Tight junction • Desmosomes • Gap Junctions

11. Special Membrane Junctions • Tight Junctions – proteins in the cell membranes that bind cells together • Makes sure nothing passes between cells • Desmosomes - small points of connective proteins that anchor cells together • Found in cells subject to heavy pulling forces • Gap Junctions – an open junction between adjacent cells • Permits chemical communication (transport) between cells

12. Membrane Transport • Interstitial Fluid – extracellular fluid largely derived from blood, but acellular • Amino acids, wastes, electrolytes, sugars, etc. • Cells need to hold a balance of these solutes between their inside and outside environments • How is this done?

13. Membrane Permeability • Membranes only allow passage to certain molecules, or only permit movement in one direction • Selectively Permeable – only certain molecules can pass

14. Active Transport • ATP is used to drive the concentration gradient across the cell membrane • Primary – ATP changes the shape of membrane proteins to shuttle specific materials across • Secondary - uses stored potential energy from primary transport to move substances • Vesicular – vesicles “gulp” materials from outside the cell by pinching off a bubble from the cell membrane

15. ELMO • Review Pages 74-75 in textbook to explain prior slide in more detail

16. Vesicular Transport • Endocytosis – cell ingests materials via vesicles • Receptor mediated • Exocytosis – cell expels material into the environment via vesicles • Phagocytosis?

17. Plasma Membrane – Resting Potential • Many cells work using electrical energy which is derived from ion separation • Muscle cells, nerve cells, etc. • How is this accomplished?

18. Electric Membrane Potential Cations (postively charged ions (K, Na) build up) + + + + K+ + + + + + K+ pump Anions (negatively charged proteins build up) - - - - - - - - - - -

19. Cytoplasm • The material between the cell membrane and the nucleus • Three major elements • Cytosol • Organelles • Inclusions

20. Cytosol • Liquid part of the cytoplasm • Consists of mostly water, but also dissolved substances such as • Salts • Sugars • proteins, • Etc.

21. Cytoplasmic Organelles • Carry out cellular metabolic processes • Specific to the kingdom of living things (e.g. chloroplasts are only found in plants)

22. Mitochondria • Powerplants of the cell • Breaks down food and uses this energy to form ATP from ADP (cellular respiration)on inner membranes (cristae) • Have their own DNA, RNA and ribosomes • Huh?

23. Ribosomes • Made of two RNA-protein subunits that work together to synthesize proteins (protein translation) • Two types • Free ribosomes – make soluble proteins • Membrane-bound organelles – make proteins for packaging or export

24. Endoplasmic Reticulum (ER) • Membranes in the cytosol that are continuous with the nuclear membrane • Rough ER – lined with ribosomes that produce proteins that are secreted from cells, also make new phospholipids and intracellular membranes • Smooth ER – Embedded with enzymes that catalyze the metabolism of proteins, fats, hormones, toxins and glycogen

25. Golgi Apparatus • Stacks of membranous sacs in the cytosol • Used to concentrate, modify and/or package proteins and lipids made by the rough ER. • Packaged proteins are called vesicles are sent into the cytosol or outside of the cell (exocytosis)

26. Lysosomes • Contain activated enzymes that may be capable of digesting all type of biological molecules • The membrane-bound lysosomes contain these dangerous substances, preventing cell damage

27. Peroxisomes • Contain extremely reactive oxygen species (ROS) that are used to detoxify certain poisons such as alcohol • Also destroy free radicals – highly reactive waste products of metabolism that can disrupt cell processes • In which cells might these be found?

28. Cytoskeleton • Consists of rods made of tubulin that run through the entire interior of the cell • Microtubules • Microfilaments • Intermediate filaments

29. Cytoskeleton Components • Microtubules • Determine cell shape and influence organelle dstribution • Microfilaments • A “web” of these filaments attach to the inner surface of the cell membrane and give the cell strength. Also helps change cell shape during mitosis/meiosis • Intermediate Filaments • Give the cell tensile strength by attaching to desmosomes

30. Centrosomes and Centrioles • Centrosomes – serve to anchor microtubulesand provide attachment points during activities such as cytokinesis, alignment of chromosomes during mitosis (mitotic spindle)

31. Cilia • Relatively short extensions of tubulin that cover cells • Enables cells to move through their environment, or move the liquid environment around themselves

32. Flagella • Long extensions of tubulin protein used for propulsion • Many microorganisms possess flagella • Only human cells that possess flagella are sperm cells

33. Inclusions • Chemical substances that may or may not be present, depending on the cell type. • Pigments • Crystals • Vacuoles • Etc.

34. The Nucleus • The nucleus is a membrane-bound organelle that serves as the central control system of the cell • All instructions for the cell’s processes are carried on genes that can be found within the DNA housed inside the nucleus

35. Nucleus • Nuclear Envelope – double layered membrane that surrounds the nucleus • Outer Layer – continuous with ER • Inner Layer – lined with lamina, filaments that hold the nuclear shape • Nuclear pores penetrate both layers, allowing some molecules to flow into and out of the nucleus

36. Nucleus • Nucleoli – dark-staining regions in the nucleus where ribosomal RNA (rRNA) is made • Chromatin – DNA wound around protein units called histones • This form of DNA allows efficient packing and storage of DNA (a nucleosome) during periods where the cell is not actively dividing

38. Nucleus - Chromosomes • During cell division, chromatin winds up to form bar-shaped structures called chromosomes • The arrangement of these structures allows the definition of different stages of cell division

39. Human Karyotype • Chromosome sizes and number can also be used to screen for genetic diseases

41. DNA Replication Helicase DNA Polymerase DNA Polymerase