Cell Structure and Function Chapter 3

Basic Characteristics of Cells Smallest living subdivision of the human body Diverse in structure and function Small

Basic Characteristics of Cells Divided into organelles –Structures and compartments in the cell –Isolation of chemical reactions –Each organelle performs a specific function

Each Cell Has Three Primary Regions Plasma Membrane Cytoplasm Nucleus

The Plasma Membrane Plasma membrane = outer casing of the cell –separates intracellular environment from the extracellular environment. Regulates movement of materials into and out of cell –a selective mechanical barrier

The Plasma Membrane Composed of Lipids, Proteins and Carbohydrates –Arranged in a lipid bilayer –“Fluid mosaic model”

Cell Membrane Components: Phospholipids one end is hydrophilic other end is hydrophobic tend to aggregate in a lipid bilayer –hydrophilic ends face outward, hydrophobic ends in the middle

Cell Membrane Components: Proteins Suspended in lipid bilayer May span layer or attached only to one surface Different functions

Types of Membrane Proteins Structural Proteins –Maintain membrane shape and integrity, movement Channel Proteins –Pore-like proteins –Enable small ions to pass Carrier proteins –Shuttle specific substances across membrane

Types of Membrane Proteins Enzymes –Catalyze specific reactions Receptor proteins –Bind cellular signals Signaling proteins / Recognition proteins –Enable cells to identify and interact with each other

Cell Membrane Components: Carbohydrates Branched polymers attached to extracellular surface Forms “sugar coating” (glycocalyx) of cells Functions –Lubricated surface –Protect underlying proteins –Cell recognition

The Cytoplasm

Cytosol semi-liquid, gel-like contains various dissolved materials, enzymes, etc. cytoskeleton = network of protein fibers throughout cytosol –structure –movement

Cytoplasmic Organelles: Ribosomes Large protein-RNA complexes Found free floating in cytosol or attached to endoplasmic reticulum synthesize proteins based on RNA codes

Cytoplasmic Organelles: Endoplasmic Reticulum (ER) Rough Endoplasmic Reticulum (RER) –Coated with ribosomes –Synthesis of proteins for: Cell membranes Interior (lumen) of membrane-bound organelles Export out of the cell

Cytoplasmic Organelles: Endoplasmic Reticulum (ER) Smooth Endoplasmic Reticulum (SER) –No ribosomes –Functions Lipid synthesis Ca 2+ storage Vesicular release

Cytoplasmic Organelles: Golgi Apparatus Stacks of flattened sacs Functions: –processes ER products into final form –sort and direct finished products to final destinations (intracellular or extracellular) –vesicles - small membrane coated chambers used to transport materials

Cytoplasmic Organelles: Lysosome Sac-like organelles which contain enzymes Break down large molecules –cell’s “digestive system” Destroy bacteria, old organelles, etc.

Cytoplasmic Organelles: Mitochondria Surrounded by two membranes Possess own DNA Power generators of the cell Convert food energy (e.g., glucose) to usable form –ATP high energy compound. major source of metabolic energy for the cell

The Nucleus

Cell's "control center" Largest organelle Surrounded by nuclear envelope Contains DNA –genetic information in form of nucleic acid polymers –instructs synthesis of proteins

DNA Structure Deoxyribonucleic acid Polymer of nucleotides –base + sugar + phosphate Four different bases –adenine (A), guanine (G), cytosine (C), thymine (T) –alternate in order –“Four-letter alphabet” Double helix –Two strands linked together by hydrogen bonds –Complementary sequences

Genes and Chromosomes Genes –sequences of DNA containing information needed to make proteins with the proper amino acid sequence DNA is wrapped around proteins to form chromosomes

Chromosomes 46 chromosomes per human cell 23 different types –pairs of homologous chromosomes –one of each pair inherited from each parent

DNA function Information in DNA used to make proteins 1.Transcription: sequence of DNA copied into an RNA (ribonucleic acid) molecule 2.Translation RNA sequence read by ribosomes to generate a protein with a specific amino acid sequence

Cell Reproduction Reproduction of cells (cell division) requires : –copying of the DNA (chromosomes) –distribution of chromosomes to daughter cells Two types of cell division –mitosis (most cells) –meiosis (gametes)

Mitosis Cells duplicate all their chromosomes One copy of each of the 46 chromosomes is distributed to each of the daughter cells.

Meiosis Occurs only in gametes Cells duplicate all chromosomes Cells undergo two separate divisions –each daughter cell has 23 total chromosomes Gametes combine to form a new cell (zygote) with 46 chromosomes