Biological Science: Inside the Cell PDF

7 Inside the Cell Lecture Presentation by Cindy S. Malone, PhD, California State Universit...

7 Inside the Cell Lecture Presentation by Cindy S. Malone, PhD, California State University Northridge © 2017 Pearson Education, Inc. Chapter 7 Opening Roadmap. © 2017 Pearson Education, Inc. The Cell Theory § All cells have 1. Nucleic acids: store and transmit information 2. Proteins: perform most of the cell’s functions 3. Carbohydrates: chemical energy, carbon, support, identity 4. Plasma membrane: selectively permeable membrane barrier © 2014 Pearson Education, Inc. Grouping Cells § According to morphology, there are two broad groupings of life: 1. Prokaryotes – Lack a membrane-bound nucleus 2. Eukaryotes – Have a nucleus § The three domains according to phylogeny, or evolutionary history, are 1. Bacteria—prokaryotic 2. Archaea 3. Eukarya—eukaryotic © 2014 Pearson Education, Inc. Prokaryotic Cells: Structural Overview § All prokaryotes lack a membrane-bound nucleus § Archaeal cell structure is still relatively poorly understood § Bacterial cells vary greatly in size and shape § Most bacteria contain several Ribosomes structural similarities – Plasma membrane Plasmid – A single chromosome Cytoplasm – Ribosomes, which synthesize Chromosome proteins Plasma membrane – Stiff cell wall Cell wall – Plasmids: extra circular DNA – Cytoskeleton: a network 1 µm of long, thin protein filaments © 2014 Pearson Education, Inc. Plasma Membrane and External Structure § The plasma membrane – Consists of a phospholipid bilayer – Has proteins that either span the bilayer Chromosome or attach to one side § Inside the membrane, all the contents of a cell – Excluding the nucleus (eukaryotes) – Are collectively termed the cytoplasm Ribosome Cytoskeleton Most prokaryotes have a cell wall Flagellum Plasma membrane Many species have an additional layer Fimbria Cell wall 50 nm Glycolipids outside the cell wall Composed of glycolipids Flagellum Some prokaryotes have tail-like flagella Fimbriae (singular: fimbria) are needlelike projections and promote attachment to Fimbriae other cells or surfaces 0.5 µm © 2014 Pearson Education, Inc. An Introduction to Eukaryotes § Eukaryotes larger than most prokaryotic cells § Many eukaryotes are multicellular and others are unicellular § Cell component structure correlates with its function § Four key differences between eukaryotic and prokaryotic cells have been identified: 1. Eukaryotic chromosomes are found Inside a membrane-bound compartment = nucleus 2. Eukaryotic cells are often much larger 3. Eukaryotic cells contain extensive amounts of internal membrane 4. Eukaryotic cells feature a diverse and dynamic cytoskeleton © 2014 Pearson Education, Inc.  (a) Generalized animal cell Nuclear envelope Cell Nucleolus Nucleus component Chromosomes Rough endoplasmic Golgi apparatus reticulum Ribosomes Centrioles Peroxisome Smooth endoplasmic reticulum Structures that occur in animal cells but not plant cells Lysosome Mitochondrion Cytoskeletal element Plasma membrane (b) Generalized plant cell Nuclear envelope Nucleolus Nucleus Chromosomes Structures that Rough endoplasmic occur in plant cells reticulum but not animal cells Ribosomes Smooth endoplasmic reticulum Cell wall Golgi apparatus Vacuole Chloroplast Peroxisome Mitochondrion Plasma membrane Cytoskeletal element On average, prokaryotes are about 10 times smaller than eukaryotic cells in diameter and about 1000 times smaller © 2014 Pearson Education, Inc. than eukaryotic cells in volume. The Nucleus Structure: The nucleus is large and highly organized § Surrounded by a double-membrane nuclear envelope § The nuclear envelope has pore-like openings § The inside is linked to fibrous proteins forming the nuclear lamina § The nucleus has a distinct region called the nucleolus Nucleus § Function: Information storage and processing – Contains the cell’s Loosely chromosomes packed sections of chromosomes Nucleolus – Ribosomal RNA Densely packed sections synthesis (in the of chromosomes nucleolus) Nuclear envelope 2 µm © 2014 Pearson Education, Inc. Ribosomes § Structure: Ribosomes are non-membranous: Are not Ribosomes considered organelles – Have large and small subunits – Contain RNA molecules and protein – Can be attached to the rough ER – Can be free in the cytosol, the fluid part of the cytoplasm § Function: Protein synthesis 100 nm © 2014 Pearson Education, Inc. Endoplasmic Reticulum 1. The rough endoplasmic reticulum (rough ER, RER) – Structure: is a network of membrane-bound tubes and sacs studded with ribosomes and is continuous with the nuclear envelope – Function: Synthesis of specific proteins 2. The smooth endoplasmic reticulum (smooth ER, SER) – Structure: The smooth endoplasmic reticulum (smooth ER, SER) is a network of membrane-bound tubes and sacs lacking ribosomes § Function: Is a reservoir for Ca2+ ions and contains enzymes that catalyze reactions involving lipids. These enzymes may – Synthesize lipids needed by the organism – Break down lipids and other molecules that are poisonous Rough endoplasmic Smooth endoplasmic reticulum reticulum Lumen of rough ER Ribosomes on outside of rough ER Lumen of smooth ER Free ribosomes in cytoplasm 200 nm 200 nm © 2014 Pearson Education, Inc. Golgi Apparatus Structure: The Golgi apparatus Is formed by a series of stacked flat membranous sacs called cisternae and has a distinct polarity, or sidedness – The cis (“this side”) surface is closest to the nucleus – The trans (“across”) surface is oriented toward the plasma membrane Function: § Processes, sorts, and ships Golgi apparatus cis proteins synthesized in the rough ER trans § cis side of a Golgi apparatus leus nuc receives products from the rough Vesicle faces side ER cis § trans side ships them out to other Lumen of Golgi apparatus organelles or the cell surface § Membranous vesicles carry Cisternae s face ne materials to and from the n s e sid mbra tra a me organelle Vesicles plas m 100 nm © 2014 Pearson Education, Inc. Lysosomes § Structure: Lysosomes are single-membrane-bound structures – Contain approximately 40 different digestive enzymes – Found only in animal cells Lysosome § Function: Lysosomes are used for – Digestion – Waste processing § Materials are delivered to the lysosomes by three processes: 1. Phagocytosis 2. Autophagy Material being 3. Receptor-mediated digested within lysosomes endocytosis 250 nm § Endocytosis is a process: The cell membrane can pinch off a vesicle to bring outside material into the cell § A type of endocytosis, pinocytosis: Brings fluid into the cell © 2014 Pearson Education, Inc. Vacuoles Structure: Vacuoles are large, membrane-bound structures found in plants and fungi Function: Most are used for storage of water and/or ions Vacuole § Some vacuoles are specialized for digestion (contain digestive enzymes) § Inside seeds, they are filled with proteins § In flower petals or fruits, they are filled with colorful pigments Vacuole § They may be packed with noxious compounds to protect leaves and stems from being eaten by predators 1 µm © 2014 Pearson Education, Inc. Peroxisomes Structure: Peroxisomes are globular organelles bound by a single membrane – They originate as buds from the ER Function: Peroxisomes are the Peroxisome center of oxidation reactions § Liver cell peroxisomes contain enzymes that remove electrons from, or oxidize, the ethanol in alcoholic beverages Peroxisome § Specialized peroxisomes in membrane Enzyme plants, called glyoxysomes core – Are packed with enzymes Peroxisome lumen – Oxidize fats to form a compound for energy storage 100 nm © 2014 Pearson Education, Inc. Mitochondria Structure: Mitochondria Have their own DNA and manufacture their own ribosomes Mitochondria have two membranes: – The inner one is folded into a series of sac-like cristae – The solution inside the cristae is the mitochondrial matrix Mitochondrion Function: ATP production is a mitochondrion’s core function Outer and inner membranes Matrix Cristae © 2014 Pearson Education, Inc. 0.1 µm Chloroplasts Structure: Most plant and algal Chloroplast cells have chloroplasts § Have a double membrane § Contain their own DNA § Chloroplasts contain Stroma membrane-bound, flattened vesicles called thylakoids: are Thylakoids stacked into piles called grana Granum § Outside the thylakoids is the Outer and inner solution called the stroma membranes 1 µm § Function: Chloroplasts convert light energy to chemical energy: They perform photosynthesis © 2014 Pearson Education, Inc. Cytoskeleton § Structure: The cytoskeleton is composed of protein fibers that gives the cell shape and structural stability § Function: – The cytoskeleton organizes all of the organelles and other cellular structures into a cohesive whole – Aids cell movement – Transport of materials within the cell The Cell Wall § Fungi, algae, and plants have a stiff outer cell wall that protects the cell § The cell wall in plants and algae is Primary made of cellulose § The cell wall in fungi is Primary made of chitin § Some plants have a secondary cell wall containing lignin © 2014 Pearson Education, Inc. Structure and Function at the Whole-Cell Level § Cell structure correlates with cell function: Type, Size, Number of organelles § Cells are dynamic living things Have interacting parts and contain constantly moving molecules (a) Animal pancreatic cell: Exports (c) Plant leaf cell: Manufactures ATP digestive enzymes. and sugar. 0.5 µm 1 µm (b) Animal testis cell: Exports (d) Brown fat cells: Burn fat to generate lipid-soluble signals. heat in lieu of ATP. 0.5 µm 1 µm © 2014 Pearson Education, Inc. How Dynamic Are Eukaryotic Cells? § Your body’s cells use and synthesize approximately 10 million ATP molecules per second § Cellular enzymes can catalyze more than 25,000 reactions per second § Each membrane phospholipid can travel the breadth of its organelle or cell in under a minute § The hundreds of trillions of mitochondria inside you – Are replaced about every 10 days – This process continues for as long as you live § The plasma membrane composition is constantly changing © 2014 Pearson Education, Inc. The Endomembrane System The endomembrane system is the primary system for protein and lipid synthesis and composed of : 1. the smooth ER 2. The rough ER 3. The Golgi apparatus § Ions, ATP, amino acids, and other small molecules diffuse randomly throughout the cell § Movement of proteins and other large molecules is energy demanding and tightly regulated © 2014 Pearson Education, Inc. The Secretory Pathway Hypothesis The secretory pathway hypothesis proposes: Proteins intended for secretion from the cell are synthesized then packaged into vesicles when they move from the RER to the Golgi apparatus and then to the cell surface. RNA Ribosome Rough ER 1. Ribosome deposits protein in ER. cis face Protein The RER and Golgi 2. Protein exits of Golgi Golgi apparatus ER. apparatus function apparatus 3. Protein enters as an integrated Golgi for processing. endomembrane system trans face 4. Protein exits of Golgi Golgi. apparatus Plasma membrane 5. Protein exits cell. © 2014 Pearson Education, Inc. The Signal Hypothesis § The signal hypothesis predicts § Proteins bound for the endomembrane system have a zip code: a 20- amino-acid-long ER signal sequence § The ER signal sequence Binds to a signal recognition particle (SRP) § That then binds to a receptor in the ER membrane § In the RER lumen, proteins are folded and glycosylated(Carbohydrates are attached to the protein) RNA Ribosome SRP Signal Cytosol sequence Lumen of rough ER SRP receptor Protein 1. Signal sequence 2. Signal binds 3. SRP binds to 4. Growing 5. Signal is synthesized. to SRP. receptor. protein sequence is enters ER. removed. © 2014 Pearson Education, Inc. Exocytosis Lumen of 1. Proteins are tagged. Golgi apparatus 1. Exocytosis: Process where some “Tags” 2. Proteins are sorted. proteins Cytosol Receptors 3. Vesicles bud. § Are sent to the cell surface in To other organelle vesicles Transport vesicles 4. Proteins interact § Fuse with the plasma membrane To pre-lysosomal To plasma with receptors. membrane 5. Delivery. § Release their contents to the compartment for secretion exterior of the cell 1. Macromolecules bind to receptors. 2. Endocytosis (“inside-cell-act”) Recycling of membrane is: proteins Endocytic vesicle 2. Endocytic vesicle forms. § Any pinching inward off of the H+ plasma membrane Early 3. Endocytic vesicle fuses with early § Resulting in the uptake of endosome H+ endosome; protons lower pH. H+ material from outside the cell 4. Early endosome Late § The sequence of events begins Vesicle from Golgi endosome matures; digestive enzymes received. apparatus when macromolecules outside the 5. Mature lysosome; cell Bind to receptors on the Lysosome macromolecules digested. © 2014 Pearson Education, Inc. Recycling Material in the Lysosome § Recycling material using: 1. Damaged organelle 1. Autophagy (literally, “same-eating”) Damaged surrounded by membrane. Damaged organelles are enclosed within Lysosome organelle 2. Delivery to an internal membrane and delivered to a lysosome. lysosome. Components are then digested and recycled 3. Small molecules recycled. 2. Phagocytosis (“eat-cell-act”): The plasma membrane of a cell 1. Detection. – Surrounds a smaller cell or food Phagosome particle and engulfs it 2. Phagosome formation. – Forms a structure called a Lysosome phagosome 3. Delivery to lysosome and digestion. – Is delivered to a lysosome, where it is taken in and digested 4. Small molecules recycled. © 2014 Pearson Education, Inc. The Dynamic Cytoskeleton § The cytoskeleton is a dense and complex network of fibers § Three types of cytoskeletal elements: 1. Actin filaments (microfilaments) 2. Intermediate filaments 3. Microtubules © 2014 Pearson Education, Inc. Actin Filaments § Actin filaments are the smallest cytoskeletal elements and made of actin molecules § Structures that help define the cell’s shape § The two distinct ends of an actin filament are referred to as plus and minus ends § Actin filaments are involved in movement and dependent on the protein myosin § Myosin is a motor protein – Converts the potential energy in ATP – Into the kinetic energy of mechanical work § Actin–myosin interactions can cause cell movements such as – Cytokinesis (next) – Cytoplasmic streaming(next) © 2014 Pearson Education, Inc. Actin–Myosin Interactions § Cytokinesis (“cell- (a) Actin and myosin interact to cause movement. moving”) is the process of Myosin cell division ATP When myosin “head” attaches to actin “Head” § In animals it occurs by the ADP + Pi region and moves, the actin filament slides use of actin filaments + end Actin - end § Myosin causes the filaments to slide past one (b) Examples of movement caused by actin–myosin interactions another and pinch the cell Cytokinesis in animals in two Actin–myosin interactions pinch § Cytoplasmic streaming is membrane in two the directed flow of cytosol and organelles Cytoplasmic streaming § In plant cells: the in plants movement occurs along Actin–myosin interactions move cytoplasm around actin filaments and is cell powered by myosin Cell wall © 2014 Pearson Education, Inc. Intermediate Filaments § Intermediate filaments: Many types exist, each consisting of a different protein – Are defined by size rather than composition – Provide structural support for the cell – Are not involved in movement § About 20 types of keratin includes fingernails, toenails, and hair § Nuclear lamins form a dense mesh under the nuclear envelope, give the nucleus its shape, anchor the chromosomes § Form a flexible skeleton that helps – Shape the cell surface – Hold the nucleus in place © 2014 Pearson Education, Inc. Microtubule Structure Structure: – Are large, hollow tubes made of tubulin dimers – Have two polypeptides, called α-tubulin and β-tubulin §In animal cells, this center is called the centrosome – It contains two bundles of microtubules called centrioles Function: (a) In animals, microtubules originate from centrosomes. §Provide stability and are involved in New microtubules movement Centrioles §Microtubules can act as “railroad Centrosome tracks”. Transport vesicles move along Matrix these tracks § Microtubules require ATP and (b) Centrioles consist of microtubules. Centrioles (oriented Centrosome kinesin for vesicle transport to occur at 90° to each other) Centrioles § Kinesin is a motor protein that converts chemical energy in ATP into mechanical work 200 µm Microtubule triplets © 2014 Pearson Education, Inc. Microtubule § Kinesin – The head region binds to the microtubule – The tail region binds to the transport vesicle § Kinesin uses these domains to “walk” along the microtubule – Through a series of conformational changes as it hydrolyzes ATP (a) Structure of kinesin (b) Kinesin “walks” along a microtubule track. Transport vesicle Tail Kinesin Stalk Every step requires energy ATP ADP + Pi Microtubule Head 5 nm - end + end © 2014 Pearson Education, Inc. Cilia and Flagella: Moving the Entire Cell § Flagella are long, hairlike projections from the cell surface that move cells – Cells Generally have just one or two flagella § Cilia are closely related to eukaryotic flagella: are Short, filament-like projections – Cells May have many cilia Cilia Flagellum 50 µm 10 µm © 2014 Pearson Education, Inc. Cilia and Flagella Structure § Flagella and cilia have an identical organization § The axoneme of cilia and flagella is – A complex “9 + 2” arrangement of microtubules § Basal body: Where axoneme attaches to the cell § The motor protein dynein Is found in the axoneme and it changes shape when ATP is hydrolyzed to “walk” up the microtubule Central microtubules (a) Transmission electron (b) micrograph of axoneme Microtubule doublet (c) Mechanism of axoneme bending 75 nm Microtubule doublet (b) Structure of axoneme Central 9 1 microtubules Spoke 8 2 Plasma Microtubule membrane doublet 3 Dynein arms 7 Link walk along 6 4 Link Dynein 5 microtubule arms doublets on Dynein one side of arms an axoneme © 2014 Pearson Education, Inc. - end + ATP: Causes dynein to walk toward minus end and pull toward plus end