Early Earth Review Early Earth 3 Possibilities for Origin of Life • • • ET origin Divine/Supernatural Evolution – from inanimate & inorganic matter Natural Selection Which one do we study? • No ET – don’t have tools to investigate • No Supernatural/Divine – can’t study in science • Yes Evolution! We, as scientists, attempt to understand and explain these forces! Origin of Organic Molecules • Primitive Atmosphere – Reducing atmosphere: H2S, NH3, CH4, CO2, H2O Lots of H+! – Energy Sources: UV & Solar radiation, lightning, and radioactive decay – Oxidizing atmospheres: Cannot form complex organic molecules spontaneously Formation of Carbon-Based Molecules • Miller & Urey – 1953 – Demonstrated complex organic molecules can form under hypothesized primitive Earth conditions Miller & Urey’s Set-up • Atmosphere: • Ocean: CH4, CO2, H2O, NH3, H2 Pool of H2O • Energy: Electrical sparks Ran Overnight… “Primordial Soup!” • Yellow “soup” with >30 complex organic molecules – a.a. and purines (Adenine & Guanine) (>50% of a cell’s dry weight comes from a.a.) Major theories: • Hydrothermal vents (in ocean floor) – Archaebacteria like hot environments; protected from UV under H2O • Pyrite or Clay Creation – Crystalline solid replication mimics cellular replication. Problem… • Space invaders brought a.a. Chapter 4: Cells What the cell are we talking about? • Cell = membrane-bound unit containing hereditary machinery and other components which allow cells to metabolize, grow, and reproduce 2 Basic Cell Types • Prokaryotes - bacteria • Eukaryotes Common Characteristics of Pro- and Eukaryotes • Plasma membrane - lipid bilayer • Nuclear region – prokaryotes - not membrane-bound; circular DNA – eukaryotes - double membrane = nuclear envelope • Cytoplasm = semi-fluid matrix – contains a.a. and proteins, sugars, etc. • Ribosomes - manufacture proteins Cell Theory • All organisms are composed of one or more cells. • Cells are the smallest living things; the basic unit of life. • All cells arise from previously existing cells. Scientists to Know (and love) • Robert Hooke - 1665 - cork under microscope; first to describe cells • Antonie von Leeuwenhoek - 1670-1690 – improved lenses; “animalcules” • Mathias Schleiden - 1838 - 1st cell theory: plants are aggregates of cells • Theodor Schwann - 1839 - added to theory: animals are aggregates of cells Size means EVERYTHING! • Small cell sizes have advantages – such as… more efficiency – Diffusion is s-l-o-w • Surface area:Volume – surface area increases as the d2 – volume increases as the d3 – i.e. volume increases MUCH faster 1 3 1 3 Total volume Total surface area Surface-tovolume ratio 27 units3 27 units3 54 units2 162 units2 2 6 SA and Volume v. Cell Diameter SA/Volume 250 200 150 Volume Surface Area 100 50 0 1 2 3 4 Cell Diameter 5 6 Characteristics of Prokaryotic Cells • small • strong cell wall • no internal membrane-bound organelles – Cyanobacteria – have chlorophyll and extensions of the plasma membrane = thylakoids • DNA forms single, circular molecule • have ribosomes • nucleoid region • The surface of prokaryotic cells may – Always are surrounded by a chemically complex cell wall, – have a capsule surrounding the cell wall, – have short projections that help attach to other cells or the substrate, or – have longer projections called flagella that may propel the cell through its liquid environment. Fimbriae Ribosomes Nucleoid Plasma membrane Cell wall Bacterial chromosome A typical rod-shaped bacterium Capsule Flagella A TEM of the bacterium Bacillus coagulans Origin of Eukaryotic Cells Endosymbiotic Theory Eukaryotic cells arose from symbiotic associations between prokaryotic and ancestral eukaryotic cells Lynn Margulis new organelles = endosymbionts ex. mitochondria, chloroplasts, & centrioles E=mc2 Comparison of Pro- and Eukaryotes • Differ in #, shape, and composition of chromosomes • Eu’s have membranes dividing cell into compartments • cell wall - no cell wall? • Most plant cells have large dynamic central vacuole filled with fluid Comparison - cont. • Plasma membranes composed of phospholipids but have different proteins embedded. – Proteins = receptors, channels, markers – FLUID MOSAIC MODEL - based on location and dynamism of these proteins in the lipid bilayer FLUID MOSAIC MODEL • First proposed by Singer and Nicholson • Proteins change tertiary structure – Channel proteins = admit specific molecules • ex. Na+ – Receptor proteins = transmit info; induce changes w/in cell when they come in contact w/ particular molecules • ex. hormones – Marker proteins = identify cell as being a particular type; belong to particular individual Putting it all together The main component of the biological membranes is phospholipids. It consists of 1. The polar head (hydrophilic) made from glycerol and phosphate and 2. The non-polar part which has two fatty acid tails (hydrophobic). Phospholipids spontaneously arrange in a bilayer. • Hydrophobic tail regions face inwards and are shielded from the surrounding polar fluid while the two hydrophilic head regions associate with the cytoplasmic and extracellular environments, respectively. • Phospholipids are held together in a bilayer by hydrophobic interactions (weak associations). • Hydrophilic/hydrophobic layers restrict entry and exit of substances. • Phospholipids allow for membrane fluidity/flexibility (important for functionality). • Phospholipids with short or unsaturated fatty acids are more fluid. • Phospholipids can move horizontally or occasionally laterally to increase fluidity. • Fluidity allows for the breaking/remaking of membranes (exocytosis/endocytosis). Typical Eukaryotic Cell Eukaryotic cells are partitioned into functional compartments The structures and organelles of eukaryotic cells perform four basic functions. 1. The nucleus and ribosomes are involved in the genetic control of the cell. 2. The endoplasmic reticulum, Golgi apparatus, lysosomes, vacuoles, and peroxisomes are involved in the manufacture, distribution, and breakdown of molecules. 3. Mitochondria in all cells and chloroplasts in plant cells are involved in energy processing. 4. Structural support, movement, and communication between cells are functions of the cytoskeleton, plasma membrane, and cell wall. Typical Animal Cell Rough Smooth endoplasmic endoplasmic reticulum reticulum NUCLEUS: Nuclear envelope Chromatin Nucleolus NOT IN MOST PLANT CELLS: Centriole Lysosome Peroxisome Ribosomes Golgi apparatus CYTOSKELETON: Microtubule Intermediate filament Microfilament Mitochondrion Plasma membrane NUCLEUS: Nuclear envelope Chromatin Nucleolus Golgi apparatus NOT IN ANIMAL CELLS: Central vacuole Chloroplast Cell wall Plasmodesma Mitochondrion Peroxisome Plasma membrane Cell wall of adjacent cell Rough endoplasmic reticulum Ribosomes Typical Plant Cell Smooth endoplasmic reticulum CYTOSKELETON: Microtubule Intermediate filament Microfilament Nucleus – Described in 1831 by Robert Brown “Repository of genetic information” directs all activities of the cell Contains chromosomes Bounded by 2 membranes = nuclear envelope Nuclear pores = embedded proteins that act as channels Nucleolus – Manufactures ribosomes Ribosomal subunits are passed out of the nucleus through the nuclear envelope Nucleus Two membranes of nuclear envelope Chromatin Nucleolus Pore Endoplasmic reticulum Ribosomes Nucleus Endoplasmic Reticulum (ER) Extensive system of channels and compartments Rough ER - ribosomes are attached Smooth ER - few ribosomes; contain enzymes that function in synthesis of lipids & carbs and in detoxification of drugs Ribosomes ER Ribosomes Cytoplasm Endoplasmic reticulum (ER) Free ribosomes Bound ribosomes Colorized TEM showing ER and ribosomes mRNA Protein Diagram of a ribosome Nucleus, Smooth, and Rough ERs Nuclear envelope Smooth ER Ribosomes Rough ER Golgi Bodies Collect, modify, package, and distribute molecules synthesized in smooth and rough ER - molecules are packaged in vesicles for transport Golgi at work “Receiving” side of Golgi apparatus Golgi apparatus 1 Transport vesicle from ER 2 Transport vesicle from the Golgi 3 4 4 “Shipping” side of Golgi apparatus Golgi apparatus Lysosomes Contain digestive enzymes Derived from Golgi Digests & recycles worn out cellular components Enzymes optimal at acidic pH Primary & Secondary lysosomes Animation Lysosome Activity Digestive enzymes Lysosome Digestion Food vacuole Plasma membrane Peroxisomes Contain oxidative enzymes Derived from smooth ER Enzymes convert fats to carbs and detoxify harmful molecules Many cell organelles are connected through the endomembrane system • Some of these membranes are physically connected and some are related by the transfer of membrane segments by tiny vesicles (sacs made of membrane). • Many of these organelles work together in the – synthesis, – storage, and – export of molecules. © 2012 Pearson Education, Inc. • The endomembrane system includes – – – – – – the nuclear envelope, endoplasmic reticulum (ER), Golgi apparatus, lysosomes, vacuoles, and the plasma membrane. © 2012 Pearson Education, Inc. Putting some pieces together… Transport vesicle buds off 4 Secretory protein inside transport vesicle mRNA Ribosome 3 Sugar chain 1 2 Polypeptide Glycoprotein Rough ER • Vacuoles are large vesicles that have a variety of functions. – Some protists have contractile vacuoles that help to eliminate water from the protist. – In plants, vacuoles may • have digestive functions, • contain pigments, or • contain poisons that protect the plant. © 2012 Pearson Education, Inc. All together now! Nucleus Nuclear membrane Rough ER Transport vesicle from Golgi to plasma membrane Smooth ER Transport vesicle from ER to Golgi Golgi apparatus Lysosome Vacuole Plasma membrane DNA-containing Organelles • All are endosymbionts. – Why does that make sense…? • Remind me: – Who were the endosymbionts? – What was that theory? Mitochondrion Nucleus Endoplasmic reticulum Some cells Engulfing of oxygenusing prokaryote Engulfing of photosynthetic prokaryote Chloroplast Host cell Mitochondrion Host cell Mitochondria Bounded by 2 membranes Matrix - folding of inner membrane - contains DNA and ribosomes Proteins involved in oxidative metabolism are located in inner mitochondrial membrane = Power House of Cell Mitochondrion Outer membrane Intermembrane space Inner membrane Cristae Matrix Chloroplasts - (Not in diagram because not in animal cells!) Bounded by 2 membranes Inner membrane defines stroma which contains DNA and ribosomes Light rxns of photosynthesis occurs in thylakoids - stacks of folded membranes in stroma Inner and outer membranes Granum Chloroplast Stroma Thylakoid Centrioles (aka centrosomes) Associated with assembly and organization of microtubules (composed of tubulin; influence cell shape, move chromosomes in cell division, provide internal structure of cilia and flagella) Centrioles are only found in ANIMAL cells! Cytoskeleton - network of protein fibers that support and anchor organelles in the cytoplasm Characteristics of Cytoskeleton • Made of 3 types of fibers: – Actin filaments = long protein fibers; provide mechanical support, shape – Microtubules = hollow tubes; cell movement – Intermediate fibers = protein ropes; intracellular tendons • Responsible for shape and organizing enzymes and macromolecular complexes w/in cytoplasm Cilia & Flagella • Used in locomotion and feeding • Bacterial & Eukaryotic flagella differ in internal organization and type of movement – Eu. flagella & cilia • 9 pairs of microtubules surrounding 2 central ones = “9 + 2” arrangement • arise from basal bodies • flagella - sometimes called undulopodia • Cilia and Flagella increase SA! Cross-Section of Eukaryotic Flagella Plasma membrane = microtubules Electron Micrograph of Cross Section of a Single Cilium (courtesy of Peter Satir) Cilia and flagella move when microtubules bend • While some protists have flagella and cilia that are important in locomotion, some cells of multicellular organisms have them for different reasons. – Cells that sweep mucus out of our lungs have cilia. – Animal sperm are flagellated. © 2012 Pearson Education, Inc. Outer microtubule doublet Central microtubules Radial spoke Dynein proteins Plasma membrane Problems with sperm motility may be environmental or genetic • In developed countries over the last 50 years, there has been a decline in sperm quality. • The causes of this decline may be – environmental chemicals or – genetic disorders that interfere with the movement of sperm and cilia. Primary ciliary dyskinesia (PCD) is a rare disease characterized by recurrent infections of the respiratory tract and immotile sperm. © 2012 Pearson Education, Inc. The extracellular matrix of animal cells functions in support and regulation • Animal cells synthesize and secrete an elaborate extracellular matrix (ECM) that – helps hold cells together in tissues and – protects and supports the plasma membrane. © 2012 Pearson Education, Inc. The extracellular matrix of animal cells functions in support and regulation • The ECM may attach to a cell through glycoproteins that then bind to membrane proteins called integrins. Integrins span the plasma membrane and connect to microfilaments of the cytoskeleton. © 2012 Pearson Education, Inc. Glycoprotein complex with long polysaccharide EXTRACELLULAR FLUID Collagen fiber Connecting glycoprotein Integrin Plasma membrane CYTOPLASM Microfilaments of cytoskelton Three types of cell junctions are found in animal tissues • Adjacent cells communicate, interact, and adhere through specialized junctions between them. – Tight junctions prevent leakage of extracellular fluid across a layer of epithelial cells. – Anchoring junctions fasten cells together into sheets. – Gap junctions are channels that allow molecules to flow between cells. © 2012 Pearson Education, Inc. Tight junctions prevent fluid from moving between cells Tight junction Anchoring junction Gap junction Plasma membranes of adjacent cells Extracellular matrix Cell walls enclose and support plant cells • A plant cell, but not an animal cell, has a rigid cell wall that – protects and provides skeletal support that helps keep the plant upright against gravity and – is primarily composed of cellulose. • Plant cells have cell junctions called plasmodesmata that serve in communication between cells. © 2012 Pearson Education, Inc. Plant cell walls Vacuole Plasmodesmata Primary cell wall Secondary cell wall Plasma membrane Cytoplasm Review: Eukaryotic cell structures can be grouped on the basis of four basic functions • Eukaryotic cell structures can be grouped on the basis of four functions: 1. 2. 3. 4. genetic control, manufacturing, distribution, and breakdown, energy processing, and structural support, movement, and communication between cells. © 2012 Pearson Education, Inc. You should now be able to: 1. Describe the importance of microscopes in understanding cell structure and function. 2. Describe the three parts of cell theory. 3. Distinguish between the structures of prokaryotic and eukaryotic cells. 4. Explain how cell size is limited. 5. Describe the structure and functions of cell membranes. © 2012 Pearson Education, Inc. You should now be able to: 6. Explain why compartmentalization is important in eukaryotic cells. 7. Compare the structures of plant and animal cells. Note the function of each cell part. 8. Compare the structures and functions of chloroplasts and mitochondria. 9. Describe the evidence that suggests that mitochondria and chloroplasts evolved by endosymbiosis. © 2012 Pearson Education, Inc. You should now be able to: 10. Compare the structures and functions of microfilaments, intermediate filaments, and microtubules. 11. Relate the structure of cilia and flagella to their functions. 12. Relate the structure of the extracellular matrix to its functions. 13. Compare the structures and functions of tight junctions, anchoring junctions, and gap junctions. © 2012 Pearson Education, Inc. You should now be able to: 14. Relate the structures of plant cell walls and plasmodesmata to their functions. 15. Describe the four functional categories of organelles in eukaryotic cells. © 2012 Pearson Education, Inc. Structural Differences between Plant and Animal Cells • • • • Cell wall MTOC? Chloroplasts Central vacuole • • • • No cell wall - no need! Centrioles No chloroplasts No central vacuole End of Cells!