Cells and TissuesA&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 AnatomyA 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