Cells and Tissues A&P Unit II

 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 Introduction

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

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.

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

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

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

 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 Membrane Transport

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

 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

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

 In vesicular transport, material moves into or out of a cell in membranous sacs.  Movement into the cell occurs through endocytosis 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

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

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

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

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

 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. The Nucleus

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

 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. The Genetic Code

 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 Protein Synthesis

 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.

 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. The Cell Life Cycle

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

 Mitosis proceeds in four stages  Prophase  Metaphase  Anaphase  telophase Mitosis

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

 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. Cell Division and Cancer

 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. Cell Diversity and Differentiation