The Cell and Its Chemistry PDF

THE CELL AND ITS CHEMISTRY Evangeline L. Martinez, MAT, LPT  The Cell Theory All organisms are composed of one or more cells. Cells are the smallest living units of all living organisms. Cells arise only by division of a previously existing cell. Ce...

THE CELL AND ITS CHEMISTRY Evangeline L. Martinez, MAT, LPT  The Cell Theory All organisms are composed of one or more cells. Cells are the smallest living units of all living organisms. Cells arise only by division of a previously existing cell. Cells vary in size and shapes. cell&itschemistry leamartinez 2  Cell Requirements Genetic material – Single circular molecule of DNA in prokaryotes – Double helix located in nucleus in eukaryotes Cytoplasm – Fills cell interior (sugars, amino acids, proteins, organelles) Plasma Membrane – Encloses the cell cell&itschemistry leamartinez 3  Cell Size Most cells are relatively small because as size increases, volume increases much more rapidly. Cell size and shape are related cell function. cell&itschemistry leamartinez 4  A Scale of Visibility cell&itschemistry leamartinez 5  Classification of Cells There are two major types of cells – prokaryotic lacks a nucleus and does not have an extensive system of internal membranes all bacteria and archaea have this cell type – eukaryotic has a nucleus and has internal membrane- bounded compartments all organisms other than bacteria or archaea have this cell type cell&itschemistry leamartinez 6  Prokaryotic Cells Prokaryotes are the simplest cellular organisms – have a plasma membrane surrounding a cytoplasm without interior compartments some bacteria have additional outer layers to the plasma membrane – cell wall comprised of carbohydrates to confer rigid structure – capsule may surround the cell wall cell&itschemistry leamartinez 7  Prokaryotic Cells The interior of the prokaryotic cell shows simple organization – cytoplasm is uniform with little or no internal support framework – ribosomes (sites for protein synthesis) are scattered throughout the cytoplasm – nucleoid region (an area of the cell where DNA is localized) not membrane-bounded, so not a true nucleus cell&itschemistry leamartinez 8  Prokaryotic Cells Other structures sometimes found in prokaryotes relate to locomotion, feeding, or genetic exchange – a flagellum (plural, flagellae) is a threadlike structure made of protein fibers that extends from the cell surface may be one or many aids in locomotion and feeding – pilus (plural, pili) is a short flagellum aids in attaching to substrates and in exchanging genetic information between cells cell&itschemistry leamartinez 9 Organization of a Prokaryotic Cell cell&itschemistry leamartinez 10  Eukaryotic Cells Eukaryotic cells are larger and more complex than prokaryotic cells – have a plasma membrane encasing the cytoplasm internal membranes form compartments called organelles the cytoplasm is semi-fluid and contains a network of protein fibers that form a scaffold called a cytoskeleton cell&itschemistry leamartinez 11  Eukaryotic Cells Many organelles are immediately conspicuous under the microscope – nucleus a membrane-bounded compartment for DNA that gives eukaryotes (literally, “true-nut”) their name – endomembrane system gives rise to the internal membranes found in the cell each compartment can provide specific conditions favoring a particular process cell&itschemistry leamartinez 12  Eukaryotic Cells Not all eukaryotic cells are alike – the cells of plants, fungi, and many protists have a cell wall beyond the plasma membrane – all plants and many protists contain organelles called chloroplasts – plants contain a central vacuole – only animal cells contain centrioles cell&itschemistry leamartinez 13  Animal Cell cell&itschemistry leamartinez 14  Plant Cell cell&itschemistry leamartinez 15  The Plasma Membrane The plasma membrane is conceptualized by the fluid mosaic model – a sheet of lipids with embedded proteins the lipid layer forms the foundation of the membrane the fat molecules comprising the lipid layers are called phospholipids cell&itschemistry leamartinez 16  The Plasma Membrane A phospholipid has a polar head and two non- (a) Phospholipid structure polar tails The polar region contains a phosphate chemical group and is water- soluble The non-polar region is comprised of fatty acids and is water-insoluble cell&itschemistry leamartinez 17  The Plasma Membrane A lipid bilayer forms spontaneously whenever a collection of phospholipids is placed in water cell&itschemistry leamartinez 18  The Plasma Membrane The interior of the lipid bilayer is completely nonpolar – no water-soluble molecules can freely cross through it – cholesterol is also found in the interior it affects the fluid nature of the membrane its accumulation in the walls of blood vessels can cause plaques plaques lead to cardiovascular disease cell&itschemistry leamartinez 19  The Plasma Membrane Another major component of the membrane is a collection of membrane proteins – some proteins form channels that span the membrane these are called transmembrane proteins – other proteins are integrated into the structure of the membrane for example, cell surface proteins are attached to the outer surface of the membrane and act as markers cell&itschemistry leamartinez 20  Proteins are embedded within the lipid bilayer cell&itschemistry leamartinez 21  The Nucleus: The Cell’s Control Center The nucleus is the command and control center of the cell – it also stores hereditary information The nuclear surface is bounded by a double- membrane called the nuclear envelope – groups of proteins form openings called nuclear pores that permit proteins and RNA to pass in and out of the nucleus cell&itschemistry leamartinez 22  The Nucleus: The Cell’s Control Center The DNA of eukaryotes is packaged into segments and associated with protein – this complex is called a chromosome the proteins enable the DNA to be wound tightly and condense during cell division when the cell is not dividing, the chromosomes exist as threadlike strands called chromatin – protein synthesis occurs when the DNA is in the chromatin form cell&itschemistry leamartinez 23  The Nucleus: The Cell’s Control Center The cell builds proteins on structures called ribosomes – ribosomes consist of ribosomal RNA (rRNA) and several different kinds of proteins Ribosomes are assembled in a region of the nucleus called the nucleolus cell&itschemistry leamartinez 24  The Nucleus cell&itschemistry leamartinez 25  The Endomembrane System The endoplasmic reticulum (ER) is an extensive system of internal membranes – some of the membranes form channels and interconnections – other portions become isolated spaces enclosed by membranes these spaces are known as vesicles cell&itschemistry leamartinez 26  The Endomembrane System The portion of the ER dedicated to protein synthesis is called the rough ER – the surface of this region looks pebbly – the rough spots are due to embedded ribosomes The portion of the ER that aids in the manufacture of carbohydrates and lipids is called the smooth ER – the surface of this region looks smooth because embedded ribosomes are scarce cell&itschemistry leamartinez 27 The endoplasmic reticulum (ER) cell&itschemistry leamartinez 28  The Endomembrane System After synthesis in the ER, the newly-made molecules are passed to the Golgi bodies – Golgi bodies are flattened stacks of membranes scattered through the cytoplasm – their numbers vary depending on the cell – their function is to collect, package, and distribute molecules manufactured in the cell – the Golgi bodies of a cell are collectively called the Golgi complex cell&itschemistry leamartinez 29  Golgi complex cell&itschemistry leamartinez 30  The Endomembrane System The ER and Golgi complex function together as a transport system in the cell cell&itschemistry leamartinez 31  The Endomembrane System The Golgi complex also gives rise to lysosomes – these membrane-bounded structures contain enzymes that the cell uses to break down macromolecules worn-out cell parts are broken down and their components recycled to form new parts particles that the cell has ingested are also digested cell&itschemistry leamartinez 32 Organelles That Harvest Energy Eukaryotic cells contain energy harvesting organelles that contain their own DNA – these organelles appear to have been derived from ancient bacteria that were taken up by eukaryotic cells – these organelles include mitochondria and chloroplasts cell&itschemistry leamartinez 33 Organelles That Harvest Energy Mitochondria are cellular powerhouses Sites for chemical reactions called oxidative metabolism The organelle is surrounded by two membranes cell&itschemistry leamartinez 34 Organelles That Harvest Energy Chloroplasts are the sites of photosynthesis The organelle is also surrounded by two membranes cell&itschemistry leamartinez 35 Organelles That Harvest Energy Both mitochondria and chloroplasts possess their own molecule of circular DNA They cannot be grown free of the cell – they are totally dependent on the cells within which they occur cell&itschemistry leamartinez 36 Organelles That Harvest Energy The theory of endosymbiosis – states that some organelles evolved from a symbiosis in which one cell of a prokaryotic species was engulfed by and lived inside of a cell of another species of prokaryote that was a precursor to eukaryotes – the engulfed species provided their hosts with advantages because of special metabolic activities – the modern organelles of mitochondria and chloroplasts are believed to be found in the eukaryotic descendants of these endosymbiotic prokaryotes cell&itschemistry leamartinez 37  Endosymbiosis cell&itschemistry leamartinez 38 Organelles That Harvest Energy In addition to the double membranes and circular DNA found in mitochondria and chloroplasts, there is a lot of other evidence supporting endosymbiotic theory – mitochondria are about the same size as modern bacteria – the cristae in mitochondria resemble folded membranes in modern bacteria – mitochondrial ribosomes are similar to modern, bacterial ribosomes in size and structure – mitochondria divide by fission, just like modern bacteria cell&itschemistry leamartinez 39  The Cytoskeleton and Related Structures The cytoskeleton is comprised of an internal framework of protein fibers that – anchors organelles to fixed locations – supports the shape of the cell – helps organize ribosomes and enzymes needed for synthesis activities The cytoskeleton is dynamic and its components are continually being rearranged cell&itschemistry leamartinez 40  The Cytoskeleton and Related Structures Three different types of protein fibers comprise the cytoskeleton – intermediate filaments thick ropes of intertwined protein – microtubules hollow tubes made up of the protein tubulin – microfilaments long, slender microfilaments made up of the protein actin cell&itschemistry leamartinez 41  The protein fibers of the cytoskeleton cell&itschemistry leamartinez 42  The Cytoskeleton and Related Structures Centrioles are complex structures that assemble microtubules in animal cells and the cells of most protists – they occur in pairs – they are found near the nuclear envelope – they are composed of microtubules cell&itschemistry leamartinez 43  Centrioles cell&itschemistry leamartinez 44  The Cytoskeleton and Related Structures Cellular motion is associated with the movement of actin microfilaments and/or microtubules – some cells “crawl” by coordinating the rearrangement of actin microfilaments – some cells swim by coordinating the beating of microtubules grouped together to form flagella or cilia cell&itschemistry leamartinez 45  The Cytoskeleton and Related Structures Cilia and Flagella are hairlike structures projecting from the cell that function to move the cell by their movements Cilium (Cilia) - the short, numerous appendages Flagellum (Flagella) – the longer, less numerous appendades cell&itschemistry leamartinez 46  Cilia and Flagella cell&itschemistry leamartinez 47  Eukaryotic Cell Surfaces and Junctions Cells interact with their environments and with each other via their surfaces. Plant cells are supported by rigid cell walls made largely of cellulose. Plant cells connect by plasmodesmata. Animal cells are embedded in an extracellular matrix consisting mainly of glycoprotein. This matrix is responsible for binding cells together in tissues. cell&itschemistry leamartinez 48  Eukaryotic Cell Surfaces and Junctions cell&itschemistry leamartinez 49  Eukaryotic Organelles and their Functions Manufacture – Nucleus, ribosomes, RER, SER, Golgi complex Breakdown – Lysosomes, peroxisomes, vacuoles Energy Processing – Chloroplasts, mitochondria Support, Movement and Communication Between Cells – Cytoskeleton, cell walls, extracellular matrix, junctions cell&itschemistry leamartinez 50  Transport of Materials Passive Transport – Diffusion – Osmosis – Facilitated Diffusion Active Transport – Endocytosis – Exocytosis cell&itschemistry leamartinez 51  Diffusion and Osmosis Movement of water and nutrients into a cell or elimination of wastes out of cell is essential for survival This movement occurs across a biological membrane in one of three ways diffusion membrane folding transport through membrane proteins cell&itschemistry leamartinez 52  Diffusion and Osmosis Molecules move in a random fashion but there is a tendency to produce uniform mixtures The net movement of molecules from an area of higher concentration to an area of lower concentration is termed diffusion Molecules diffuse down a concentration gradient from higher to lower concentrations – diffusion ends when equilibrium is reached cell&itschemistry leamartinez 53  Essential Biological Process: Diffusion cell&itschemistry leamartinez 54  Diffusion and Osmosis The concentration of all molecules dissolved in a solution is called the osmotic concentration of the solution – if the osmotic concentrations of two solutions is equal, the solutions are each called isotonic – if two solutions have unequal osmotic concentration, the solution with the higher solute concentration is said to be hypertonic, and the solution with the lower solute concentration is said to be hypotonic cell&itschemistry leamartinez 55  Diffusion and Osmosis Movement of water by osmosis into a cell causes pressure called osmotic pressure – enough pressure may cause a cell to swell and burst – osmotic pressure explains why so many cell types are reinforced by cell walls cell&itschemistry leamartinez 56  Osmotic pressure in plants and animal cells cell&itschemistry leamartinez 57  Forms of Endocytosis Phagocytosis is endocytosis of particulate (solid) matter Pinocytosis is endocytosis of liquid matter cell&itschemistry leamartinez 58  Exocytosis cell&itschemistry leamartinez 59  Chemistry of Life Inorganic Compounds – Water – Gases – Minerals Organic Compounds – Carbohydrates – Proteins – Lipids – Nucleic acids – Vitamins cell&itschemistry leamartinez 60  Hydrogen Bonds Give Water Unique Properties Water is essential for life – the chemistry of life is water chemistry Water is a polar molecule – water can form hydrogen bonds – hydrogen bonding confers on water many different special properties cell&itschemistry leamartinez 61  Hydrogen Bonds Give Water Unique Properties Heat Storage – water temperature changes slowly and holds temperature well Ice Formation – few hydrogen bonds break at low temperatures water becomes less dense as it freezes because hydrogen bonds stabilize and hold water molecules farther apart High Heat of Vaporization – water requires tremendous energy to vaporize because of all the hydrogen bonds that must be broken – when water vaporizes, it takes this heat energy with it, allowing for evaporative cooling cell&itschemistry leamartinez 62  Ice formation cell&itschemistry leamartinez 63  Hydrogen Bonds Give Water Unique Properties Water molecules are attracted to other polar molecules – cohesion – when one water molecule is attracted to another water molecule – adhesion – when polar molecules other than water stick to a water molecule cell&itschemistry leamartinez 64  Hydrogen Bonds Give Water Unique Properties High polarity – in solution, water molecules tend to form the maximum number of hydrogen bonds hydrophilic molecules are attracted to water and dissolve easily in it – these molecules are also polar and can form hydrogen bonds hydrophobic molecules are repelled by water and do not dissolve – these molecules are nonpolar and do not form hydrogen bonds cell&itschemistry leamartinez 65  How salt dissolves in water cell&itschemistry leamartinez 66  Water Ionizes The covalent bond within a water molecule sometimes breaks spontaneously H2O « OH- + H+ Water Hydroxide Hydrogen This produces a positively hydrogen ion (H+) and a negatively charged hydroxide ion (OH-) cell&itschemistry leamartinez 67  Water Ionizes The amount of ionized hydrogen from water in a solution can be measured as pH The pH scale is logarithmic, which means that a pH scale difference of 1 unit actually represents a 10-fold change in hydrogen ion concentration cell&itschemistry leamartinez 68  The pH scale cell&itschemistry leamartinez 69  Water Ionizes Pure water has a pH of 7 – there are equal amounts of [H+] relative to [OH-] Acid – any substance that dissociates in water and increases the [H+] – acidic solutions have pH values below 7 Base – any substance that combines with [H+] when dissolved in water – basic solutions have pH values above 7 cell&itschemistry leamartinez 70  Water Ionizes The pH in most living cells and their environments is fairly close to 7 – proteins involved in metabolism are sensitive to any pH changes Organisms use buffers to minimize pH disturbances – a buffer is a chemical substance that takes up or releases hydrogen ions cell&itschemistry leamartinez 71  Organic Compounds Carbohydrates – major source of energy Proteins – for tissue repair Lipids – constituents of membranes, also a source of energy Nucleic Acids – genetic material and for protein synthesis cell&itschemistry leamartinez 72 cell&itschemistry leamartinez 73