Transcript Polymers
The Living Cell Chapter 21 Great Idea: Life is based on chemistry, and chemistry takes place in cells Chapter Outline • • • • The Nature and Variety of Cells How Does a Cell Work? Metabolism: Energy and Life Cell Division The Nature and Variety of Cells The Cell Theory • All living things are composed of cells • The cell is the fundamental unit of life • All cells arise from previous cells Observing Cells: The Microscope How Does a Cell Work? Cell Membranes • Cell Membranes – Isolate cell – Separates cell parts • Transport – Individual molecules – Specific materials • channels • Receptors – Bind molecules • Cell Wall – Plants Plant Cell There are two types of cells on Earth: Prokaryotic and Eukaryotic. The former appeared first, and strong evidence indicates that the latter evolved from the former via endosymbiotic relationship. Prokaryotic cells include all bacteria and the blue-green algae. Fossil evidence shows that they have lived on earth for at least 3.8 billion years. The DNA in prokaryotic cells is not enclosed within a membrane-bound nucleus as is the DNA in eukaryotic cells. Schematic of a Eukaryotic Cell The information required for producing all of the constituents of a cell is contained in the DNA in the chromosomes in the nucleus The Nucleus • Nucleus – Contains genetic material • Prokaryotes – No nucleus • Eukaryotes – Nucleus • Double Membrane Cell, the factories of life • You have about 10 trillion cells. • Factories have: – Front office- paperwork – Building- Bricks and Mortar- loading docks – Production Units – Power Plant Cell, the factories of life • Paperwork- the plan- DNA • Building- cell walls. – Protein & Receptors- loading dock Cell, the factories of life • Production- organelles- perform the chemical functions • Power Plant- Mitochondria receive carbohydrates, fats and proteins and “burn” to produce energy • Synthesis- site of protein synthesis (controlled by RNA next chapter) Photograph of a cell of maize rust. The dark boundary is the cell wall, made from cellulose. The nucleus takes up almost half the area of the central part of the cell. Mitochondria • “Sausage“ shaped organelles (specialized structures in cells) where molecules derived from glucose react to produce the cells energy An organelle- mitochondria. The Energy Organelles: Chloroplasts and Mitochondria • Organelle – Specialized structure in cell • Chloroplasts – Energy transformation • chlorophyll – Plant cells only – Double membrane • Mitochondria – Produces cells energy – Double membrane – Own DNA Cytoskeleton • Cytoskeleton – – – – Gives cell shape Anchors Allows movement Transport system • Within cell • Structure – Strong filaments – Complex web Metabolism: Energy and Life Cells Energy • Cells store energy in various ways. • The most common is in a molecule adenosine triphosphate or ATP. • Making ATP is endothermic so cells can make ATP and then release that energy when it’s needed. The Cell’s Energy Currency • Adenosine triphosphate (ATP) – Provides energy • Structure – 3 phosphate groups – Sugar molecule: ribose – adenine • Function – Removal of phosphate group provides energy The ATP reaction ATP ADP + PO 4 + energy The tri-phosphate becomes a di-phosphate Photosynthesis • Photosynthesis – Convert sunlight to energy • Process – Energy + CO2 + H2O carbohydrate + O2 • Colors Glycolysis: The First Step in Energy Generation in the Cell • Respiration – Oxidation of carbohydrate – Retrieves energy in glucose – Aerobic • Process – Glycolysis • Split glucose • Result – Pyruvic acid – 2 ATP – 2 energy carriers • Convert energy carriers to 2-3 ATP – 1 molecule glucose = 6-8 ATP Fermentation: A Way to Keep Glycolysis Going • Fermentation – Anaerobic – Inefficient • Yeast – alcohol • Animal cells – Lactic acid The Final Stages of Respiration • Krebs cycle – – – – Glucose broken down CO2 produced ATP Energy-carrying molecules • Result – 36-38 ATP Cell Division Mitosis • Mitosis – Cell division – Not for sexual reproduction • Chromosomes • Process – – – – Copy chromosomes Spindle fibers Migration of chromosomes Nuclear membrane reforms Meiosis • Meiosis – Sexual reproduction – 1 cell forms 4 gametes • Gametes are genetically unique • Process – – – – Copy chromosomes Crossing over Segregation Segregation again • Result – 4 daughter cells – ½ normal chromosomes Meiosis VIRUS Virus occupy a twilight zone between the worlds of living and nonliving things. Criteria commonly applied for living things include (1) independent motility, (2) irritability (the ability to respond to certain environmental stimuli), (3) the ability to reproduce, and (4) the ability to specify the genetic composition of progeny. Viruses can have a wide variety of shapes and sizes. This diagram of a bacterial virus shows the protein coat containing DNA at the head. The tail fibers at the bottom attach the virus to the cell wall. DNA is then injected into the cell through the cylindrical core. A diagram of the HIV virus. The reverse transcriptase is the enzyme that initiates reverse transcription in the virus. THE AIDS VIRUS Human immunodeficiency virus (HIV) was shown in 1984 to be the cause of the dreaded condition called immune deficiency syndrome (AIDS). In 2004 40 million people lived with it (1.1 million Americans) 5 million people acquired HIV 3.1 million people died of it The central dogma of molecular biology HIV is a human retrovirus, the third such virus to be identified. Retroviruses (retro--from Latin means "turning back" are named after the crucial step in their growth cycle that involves the reversal of transcription, the first half of the "central dogma of biology" Organic Molecules Four Basic Characteristics • Most molecules based on chemistry of carbon – Organic molecules • Life’s molecules form from few elements – H, O, C, N97.5% of body weight • Molecules composed of simple building blocks – Arranged differently • Shape determines behavior – Determines ability for bonding Chemical Shorthand • No H atoms or bonds to H are shown • C atoms are not shown explicitly Shorthand