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Transcript
Basic Characteristics of Cells Cell Structure and Function • Smallest living subdivision of the human body Chapter 3 • 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 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 Each Cell Has Three Primary Regions • Plasma Membrane • Cytoplasm • Nucleus The Plasma Membrane • Composed of Lipids, Proteins and Carbohydrates – Arranged in a lipid bilayer – “Fluid mosaic model” – a selective mechanical barrier 1 Cell Membrane Components: Phospholipids • one end is hydrophilic • other end is hydrophobic • tend to aggregate in a lipid bilayer Cell Membrane Components: Proteins • Suspended in lipid bilayer • May span layer or attached only to one surface • Different functions – hydrophilic ends face outward, hydrophobic ends in the middle 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 Cell Membrane Components: Carbohydrates 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 The Cytoplasm • Branched polymers attached to extracellular surface • Forms “sugar coating” (glycocalyx) of cells • Functions – Lubricated surface – Protect underlying proteins – Cell recognition 2 Cytosol • semi-liquid, gel-like • contains various dissolved materials, enzymes, etc. • cytoskeleton = network of protein fibers throughout cytosol – structure – movement 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: 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: 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) • Smooth Endoplasmic Reticulum (SER) – No ribosomes – Functions • Lipid synthesis • Ca2+ storage • Vesicular release Cytoplasmic Organelles: Lysosome • Sac-like organelles which contain enzymes • Break down large molecules – cell’s “digestive system” • Destroy bacteria, old organelles, etc. 3 Cytoplasmic Organelles: Mitochondria • Surrounded by two membranes • Possess own DNA • Power generators of the cell • Convert food energy (e.g., glucose) to usable form 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 – ATP • high energy compound. • major source of metabolic energy for the cell DNA Structure • Deoxyribonucleic acid • Polymer of nucleotides Genes and Chromosomes • Genes – base + sugar + phosphate – sequences of DNA containing information needed to make proteins with the proper amino acid sequence • 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 • DNA is wrapped around proteins to form chromosomes Chromosomes DNA function • • 46 chromosomes per human cell • 23 different types – pairs of homologous chromosomes – one of each pair inherited from each parent 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 4 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 5