Cells and Tissues

1. Cells and Tissues A&P Unit II

2. Introduction • Modern cell theory incorporates several basic concepts • Cells are the building blocks of all plants and animals • Cells are the smallest functioning units of life • Cells are produced by the division of pre-existing cells • Each cell maintains homeostasis

3. Studying Cells Electron microscopes are important tools used in cytology; the study of the structure and function of cells.

4. An Overview of Cellular Anatomy A cell is surrounded by extracellular fluid (ECF). The cells outer boundary, the cell membrane, separates the cytoplasm, or cell contents from the ECF.

5. Cell Membrane • The functions of the cell membrane include: • Physical isolation • Control of the exchange of materials with the cells surroundings • Sensitivity • Structural support

6. Membrane Structure The cell membrane, or plasma membrane, contains lipids, proteins ,and carbohydrates Its major components, lipid molecules, form a phospholipid bilayer

7. Membrane proteins may function as: • receptors, • Channels • Carriers • Enzymes • Anchors • Identifiers • See Table 3-2

8. Membrane Transport Cell membranes are selectively permeable Diffusion is the net movement of material from an area where its concentration is relatively high to an area where its concentration is lower Diffusion occurs until the concentration gradient is eliminated

10. Osmosis is the diffusion of water across a membrane is response to differences in concentration The force of movement is osmotic pressure

12. In filtration, hydrostatic pressure forces water across a membrane. If membrane pores are large enough, molecules of solute will be carried along Facilitated diffusion is a type of carrier-mediated transport and requires the presence of carrier proteins in the membrane

13. Active transport mechanisms consume ATP but are independent of concentration gradients.

14. In vesicular transport, material moves into or out of a cell in membranous sacs. • Movement into the cell occurs throughendocytosis which is an active process (uses ATP) including: • Receptor-mediated endocytosis • Pinocytosis (cell drinking) • Phagocytosis (cell eating) Movement out of the cell occurs through exocytosis

16. The Cytoplasm The cytoplasm surround the nucleus and contains a fluid cytosol and intracellular structures called organelles.

17. The Cytosol The cytosol differs in composition from the extracellular fluid that surrounds most cells of the body.

18. Organelles • Membrane-enclosed organelles are surrounded by lipid membranes that isolate them from the cytosol • They include: • Endoplasmic reticulum • Nucleus • Golgi apparatus • Lysosomes • Mitochondria

19. Organelles that are not membrane-enclosed are always in contact with the cytosol. • They include • Cytoskeleton • Microvilli, • centrioles, • Cilia • Flagella • Ribosomes.

20. The Nucleus The nucleus is the control center for cellular operations. It is surrounded by a nuclear envelope through which it communicates with the cytosol by way of nuclear pores.

21. Chromosome structure The nucleus controls the cell by directing the synthesis of specific proteins using information stored in the DNA of chromosomes.

22. The Genetic Code The cell’s information storage system, the genetic code, is called a triplet code because a sequence of three nitrogenous bases identifies a single amino acid. Each gene consists of all the triplets needed to produce a specific protein.

23. Protein Synthesis Protein synthesis includes both transcription, which occurs in the nucleus and translation which occurs in the cytoplasm During transcription a strand of messenger RNA (mRNA) is formed and carries protein-making instructions from the nucleus to the cytoplasm

24. During translation a functional protein is constructed from the information contained in an mRNA strand. Each triplet of nitrogenous bases along the mRNA strand is a codon. The sequence of codons determines the sequence of amino acids in the protein. Molecules of transfer RNA (tRNA) bring amino acids to the ribosomes involved in translation.

26. The Cell Life Cycle Cell division is the reproduction of cells. Apoptosis is the genetically controlled death of cells. Mitosis is the nuclear division of somatic cells Sex cells are produced by meiosis.

27. Interphase Most somatic cells are in interphase most of the time. Cells preparing for mitosis undergo DNA replication in this phase

28. Mitosis • Mitosis proceeds in four stages • Prophase • Metaphase • Anaphase • telophase

29. Cytokinesis During cytokinesis, the cytoplasm divides, producing two identical daughter cells

30. Cell Division and Cancer Abnormal cell growth and division forms benign tumor or malignant tumors within a tissue Cancer is a disease characterized by the presence of malignant tumors. Over time cancer cells tend to spread to new areas of the body.

31. Cell Diversity and Differentiation Differentiation is the specialization that produces cells with limited capabilities. These specialized cells form organized collections called tissues, each of which has specific functional roles.