Chapter 4 Physiology of Cells

1. Chapter 4Physiology of Cells Sean Ragain

2. Movement of Substances through Cell Membranes (Table 4-1) Passive transport – does not require any energy (ATP) expenditure of the cell; substances move from high concentration to low concentration

3. Movement of Substances through Cell Membranes Two types of passive transport Diffusion – molecules move through the membrane from high concentration to low As molecules diffuse, a state of equilibrium will occur Osmosis – Diffusion of water through a selectively permeable membrane

4. Osmosis Diffusion of water through a selectively permeable membrane, which limits the diffusion of at least some of the solute particles Water pressure that develops as a result of osmosis is called osmotic pressure

5. Osmosis Isotonic—two fluids that have the same potential osmotic pressure (Figure 4-5) Hypertonic—“higher pressure”; cells placed in solutions that are hypertonic to intracellular fluid always shrivel as water flows out of cell Hypotonic—“lower pressure”; cells placed in a hypotonic solution may swell as water flows into them

6. Facilitated Diffusion (mediated passive transport) A special kind of diffusion whereby movement of molecules is made more efficient by the action of transporters embedded in a cell membrane Transports substances down a concentration gradient

7. Movement of Substances through Cell Membranes Active transport – requires the expenditure of metabolic energy by the cell – REQUIRES ATP Transport by pumps Pumps are membrane transporters that move a substance against its concentration gradient – the opposite of diffusion Examples: calcium pumps (Figure 4-8) and sodium-potassium pumps (Figure 4-9)

8. Calcium Pumps In the membranes of muscle cells – allow the cell to force nearly all intracellular calcium ions into special compartments or out of the cell entirely Muscle cells can not function properly if calcium ion concentrations are not kept low during rest

9. Sodium Potassium Pumps Operates in the membranes of all human cells Essential for cell survival Transports sodium ions out and potassium ions into the cell Creates a gradient of sodium and potassium ions Very important in neuron function and the polarization of neuronal cells

10. Transport by Vesicles An active transport processes Transport by vesicles – allows substances to enter or leave the interior of a cell without actually moving through its plasma membrane

11. Endocytosis Endocytosis – the plasma membrane “traps” some extracellular material and brings it into the cell in a vesicle Two basic types of endocytosis (Figure 4-10): Phagocytosis—“condition of cell-eating”; large particles are engulfed by the plasma membrane and enter the cell in vesicles; vesicles fuse with lysosomes, where the particles are digested

12. Exocytosis An active transport processes Process by which large molecules, notably proteins, can leave the cell even though they are too large to move out through the plasma membrane Provides a way for new material to be added to the plasma membrane

13. Cell Metabolism Metabolism is the set of chemical reactions in a cell Catabolism – breaks large molecules into smaller ones; usually releases energy Anabolism – builds large molecules from smaller ones; usually consumes energy

14. Enzymes Enzymes are proteins that act as chemical catalysts (reduce activation energy needed for a reaction) and regulate cell metabolism Chemical structure of enzymes Proteins of a complex shape Active Site Cofactors of enzymes include vitamins and minerals

15. General Functions of Enzymes Regulating metabolic pathways Most enzymes catalyze reversible reactions Enzymes are continually destroyed and are replaced Many enzymes are synthesized as inactive proenzymes

16. Cell Metabolism General functions of enzymes (cont.) Enzymes are continually being destroyed and are continually being replaced Many enzymes are first synthesized as inactive proenzymes – proinsulin

17. DNA Deoxyribonucleic acid (DNA) A double-helix polymer that functions to transfer information, encoded in genes, that directs the synthesis of proteins (Figure 4-22) Gene – a segment of a DNA molecule that consists of approximately 1000 pairs of nucleotides and contains the code for synthesizing one polypeptide (Figure 4-23)

18. Cell Metabolism Anabolism – begins with reading the “genetic code” Protein synthesis is a central anabolic pathway in cells (Table 4-2) Transcription (1) Translation (2) Central Dogma DNA RNA protein 2. 1.

19. Transcription Transcription – mRNA forms along a segment of one strand of DNA (Figure 4-24) Base Pair Rules A-U, C-G Occurs in the Nucleus Be able to transcribe a segment of DNA

20. Translation, Figure 4-26 mRNA associates with a ribosome in the cytoplasm tRNA molecules bring specific amino acids to the mRNA at the ribosome; the type of amino acid is determined by the fit of a specific tRNA’s anticodon with mRNA’s codon (Figure 4-27)

21. Cell Metabolism Anabolism (cont.) Genome The genes of the cell Proteome All the proteins synthesized by a cell make up the cell’s proteome All the proteins synthesized in the whole body are collectively called the human proteome

22. Growth and Reproduction of Cells Cell growth – depends on using genetic information in DNA to make the structural and functional proteins needed for cell survival Cell reproduction – ensures that genetic information is passed from one generation to the next

23. Growth and Reproduction of Cells Production of cytoplasm – more cell material is made, including growth and/or replication of organelles and plasma membrane Occurs during Interphase

24. DNA replication (Table 4-4) Replication of the genome prepares the cell for reproduction; mechanics are similar to RNA synthesis DNA strand uncoils and strands come apart Along each separate strand, a complementary strand forms The two new strands are called chromatids, instead of chromosomes Chromatids are attached in pairs at the centromere

25. Chromosomes 23 Pairs of Human Chromosomes 46 Total Chromosomes 1 set from mother and 1 set from father

26. Cell Growth Growth phase of the cell life cycle can be subdivided into the first growth phase (G1), the [DNA] synthesis phase (S), and the second growth phase (G2)

27. Cell Reproduction Cell reproduction – cells reproduce by splitting themselves into two smaller daughter cells (Table 4-5) Mitosis – the process of organizing and distributing nuclear DNA during cell division has four distinct phases (Figure 4-31) – Prophase, Metaphase, Anaphase, Telophase

28. Prophase Prophase – “before-phase” Nuclear envelope falls apart as the chromatids coil up to form chromosomes As chromosomes are forming, centriole pairs move toward the poles of the parent cell, spindle fibers are constructed between them Nucleolous disappears

29. Metaphase Metaphase – “position-changing phase” Chromosomes align along the “middle” of the mitotic spindle Each chromatid attaches to a spindle fiber

30. Anaphase Anaphase – “apart phase” Centromere of each chromosome split to form two chromosomes Each chromosome is pulled apart toward the nearest pole

31. Telophase Telophase – “end phase” DNA uncoils into chromatin Nucleolous reappears After completion of telophase, each daughter cell begins interphase to develop into a mature cell

32. Cytokinesis Division of the Cytoplasm Begins in late anaphase and is completed at the end of telophase

33. Meiosis Meiosis (Figure 4-32; see also Figure 33-1) Cell Division that occurs in gametes (sex cells) Results in 4 haploid gametes with 23 chromosomes

34. Regulating the Cell Life Cycle Cyclin-dependent kinases (CDKs) are activating enzymes that drive the cell through the phases of its life cycle Cyclins are regulatory proteins that control the CDKs and “shift” them to start the next phase

35. Cycle of Life: Cells Different types of cells have different life cycles Advancing age creates changes in cell numbers and in their ability to function effectively Examples of decreased functional ability include muscle atrophy, loss of elasticity of the skin, and changes in the cardiovascular, respiratory, and skeletal systems

36. The Big Picture: Cells and the Whole Body Most cell processes are occurring at the same time in all of the cells throughout the body The processes of normal cell function result from the coordination dictated by the genetic code

37. Mechanisms of Disease Cellular Diseases Cell Transport Cell Membrane Receptors Cell Reproduction DNA and protein synthesis Infections