Biology 2e Chapter 4 Cell Structure PDF

BIOLOGY 2E Chapter 4 CELL STRUCTURE Lecture PowerPoint Slides This work is licensed under a Creative Commons Attribution-NonCommercial- ShareAlike 4.0 International License.  CHAPTER 4 : CELL STRUCTUR...

BIOLOGY 2E Chapter 4 CELL STRUCTURE Lecture PowerPoint Slides This work is licensed under a Creative Commons Attribution-NonCommercial- ShareAlike 4.0 International License.  CHAPTER 4 : CELL STRUCTURE 4.1 Studying Cells 4.2 Prokaryotic Cells 4.3 Eukaryotic Cells 4.4 The Endomembrane System and Proteins 4.5 The Cytoskeleton 4.6 Connections between Cells and Cellular Activities 4.1 Studying Cells Learning Objectives By the end of this section, you will be able to do the following: ▪ Describe the role of cells in organisms ▪ Compare and contrast light microscopy and electron microscopy ▪ Summarize cell theory THE FUNDAMENTAL UNITS OF LIFE Cells are the building blocks of all organisms In single-celled organisms the cell is everything  Multicellular organisms are organized in a hierarchy Cells are the basic unit Tissues are composed of interconnected cells with a common function Several tissues combine to form an organ Organs working together make up an organ system Multiple systems that function together form the entire organism Biological levels of organization Cell size varies. Most are too small to be seen by the naked eye Microscopes make small cells easier to see. Magnification and Resolving Power: The two parameters most important in microscopy.  Magnification Magnification is the process of enlarging an object's appearance https://www.microbehunter.com/how-much-magnification-do-i-need/  Resolution Resolving power is the ability of a microscope to distinguish two adjacent structures as separate. The higher the resolution, the better the clarity and detail of the image Microscopes with different optical systems produce images for different studies Compound light microscopes bend visible light to provide magnification Transparent objects (like cells) must be treated with chemical stains to distinguish different parts  Electron Microscopes Electron microscopes achieve higher magnification and resolution using beams of electrons Transmission electron microscopes can show fine detail within cells Scanning electron microscopes provide 3-D exterior views  Cell Theory An underlying principle of biology – Cells are basic units of life – All living organisms made of cells – All cells come from preexisting cells  Cells have 4 common components 1) An enclosing plasma membrane which separates the cell’s interior from the environment 2) Cytoplasm made of cytosol in which other components of the cell are found 3) DNA -- the genetic material of the cell 4) Ribosomes which synthesize proteins 4.1 Studying Cells Learning Objectives You should now be able to do the following: ▪ Describe the role of cells in organisms ▪ Compare and contrast light microscopy and electron microscopy ▪ Summarize cell theory 4.2 Prokaryotic Cells Learning Objectives By the end of this section, you will be able to do the following: Name examples of prokaryotic and eukaryotic organisms Compare and contrast prokaryotic and eukaryotic cells Describe the relative sizes of different cells Explain why cells must be small  Characteristics of Prokaryotes Organisms in the domains Archaea & Bacteria are prokaryotes Prokaryotes lack membrane-enclosed internal compartments (e.g. nucleus) Most have a cell wall containing peptidoglycan Prokaryotes are believed to be much like the first cells Generalized structure of a prokaryotic cell Chromosomal DNA is localized in a nucleoid Ribosomes are in the cytoplasm The cell membrane is surrounded by a cell wall The other structures shown may be present in some, but not all, bacteria Prokaryotic cells are smaller than eukaryotic cells Reasons for small size of prokaryotic cells: – Surface area to volume ratio is more favorable for moving material in and out of the cell – They lack modifications found in eukaryotes that aid internal transport Factors Limiting Cell Size Ratio of surface to volume – As cells get bigger, volume increases faster than surface area – Materials such as oxygen and carbon dioxide require the surface area of the cell membrane to efficiently move in and out of the cell. 4.2 Prokaryotic Cells Learning Objectives You should now be able to do the following: Name examples of prokaryotic and eukaryotic organisms Compare and contrast prokaryotic and eukaryotic cells Describe the relative sizes of different cells Explain why cells must be small 4.3 Eukaryotic Cells Learning Objectives By the end of this section, you will be able to do the following: Describe the structure of eukaryotic cells Compare animal cells with plant cells State the role of the plasma membrane Summarize the functions of the major cell organelles  Eukaryotic Cells Eukaryotic organisms include plants, animals, fungi, and many microorganisms. Cells of eukaryotes have internal membranes modification of work by Rl/Wikimedia Commons. “mushroom”: modification of work by Chris Wee; Glaucocystis. (credit: By ja:User:NEON / commons:User:NEON_ja - Own work, CC BY-SA 2.5, https://commons.wikimedia.org/w/index.php?curid=1706641 Eukaryotic plasma membrane Phospholipid bilayer with embedded proteins. Cytoplasm: Region between the plasma membrane and the nuclear envelope This consists of organelles suspended in gel-like cytosol plus the cytoskeleton. 70-80% of the cytoplasm is water but it has semi-solid consistency due to proteins within it.  Nucleus Usually only one per cell – Usually the largest organelle – Bigger itself than most prokaryotic cells  Nuclear Envelope Nuclear envelope is a double membrane (two phospholipid bilayers) – Separates DNA from cytoplasm Nuclear pores perforate this membrane – Connect nucleoplasm to cytoplasm – Regulate flow of molecules back & forth  Nucleolus This is a region inside nucleus where ribosomal RNA (rRNA) is synthesized and ribosomes are assembled from rRNA & proteins  Ribosomes Made of two different-sized subunits Made of rRNA and proteins During protein synthesis, ribosomes assemble amino acids into proteins  Mitochondrion Converts chemical energy in glucose to more useful form (ATP) (cellular respiration, Chapter 7) Inner membrane is folded – Folds are called cristae – Area enclosed is the mitochondrial matrix Mitochondria have their own DNA and ribosomes (distinct from the ribosomes in the cytoplasm and from the nuclear DNA)  Chloroplasts Chloroplasts are double-membrane organelles; have their own ribosomes and DNA like mitochondria do The inner membrane encloses an aqueous fluid (stroma) that contains a set of interconnected and stacked fluid-filled membrane sacs called thylakoids Each stack of thylakoids is a granum (plural = grana) Chloroplast is the site of photosynthesis in plants (to be covered in Chapter 8)  Endosymbiosis It is hypothesized that mitochondria and chloroplasts originated as independent prokaryotic organisms. These became endosymbionts of the prokaryotic ancestors of the eukaryotes. This explains why mitochondria and cloroplasts have their own distinct DNA and ribosomes, with structure similar to the DNA and ribosomes in prokaryotic cells Also, the size of these organelles is similar to that of independent prokaryotes.  Centrosome The centrosome consists of two centrioles that lie at right angles to each other Each centriole is a cylinder made up of nine triplets of microtubules Non-tubulin proteins (indicated by the green lines) hold the microtubule triplets together Contrasting Animal and Plant Cells Plant cells have – cell wall – chloroplasts – large central vacuole Animal cells do not have these structures Animal Cell Plant Cell  Plant Cell Walls The cell wall is a rigid protective structure external to the plasma membrane Plant cell walls differ from prokaryotes because they are made up of cellulose rather than peptidoglycan. Cellulose molecule  The Central Vacuole Plant cells have a large vacuole that occupies most of the area of the cell This central vacuole helps regulate water concentration under changing environmental conditions, and contributes to cell expansion. 4.3 Eukaryotic Cells Learning Objectives You should now be able to do the following: Describe the structure of eukaryotic cells Compare animal cells with plant cells State the role of the plasma membrane Summarize the functions of the major cell organelles 4.4 The Endomembrane System and Proteins Learning Objectives By the end of this section, you will be able to do the following: List the components of the endomembrane system Recognize the relationship between the endomembrane system and its functions  The Endomembrane System The endomembrane system consists of internal membranes and organelles in eukaryotic cells that work together to modify, package, and transport lipids and proteins. Endomembrane system includes – nuclear envelope – lysosomes – vesicles – endoplasmic reticulum – Golgi apparatus – plasma membrane  Lysosomes Lysosomes in animal cells contain digestive enzymes Lysosomes break down large biomolecules and worn-out organelles See in the illustration how the lysosome fuses with another organelle and digests the contents:  Endoplasmic reticulum (ER) Interconnected membranous sacs and tubules. The hollow portion of the ER tubules is called the lumen or cisternal space. The membrane of the ER is continuous with the nuclear envelope. Rough ER (RER) modifies proteins. Smooth ER (SER) synthesizes lipids.  Rough Endoplasmic Reticulum Ribosomes attached to the cytoplasmic surface manufacture proteins New proteins are modified (by folding or the acquisition of side chains) in the lumen of the RER Modified proteins are either incorporated into cellular membranes or secreted from the cell Smooth Endoplasmic Reticulum The SER is continuous with the RER but has few or no ribosomes on its cytoplasmic surface.  Functions of the Smooth ER Synthesis of – Carbohydrates – Lipids – Steroid hormones Detoxification of medications and poisons Storage of Ca++ In muscle cells, a specialized SER called the sarcoplasmic reticulum stores Ca++ needed for contractions of the muscle cells.  Golgi Apparatus Lipids or proteins within transport vesicles still need to be sorted, packaged, and tagged so that get to the right place This occurs in the Golgi apparatus (also called the Golgi body or Golgi complex) which consists of a series of flattened membranes  Golgi Apparatus The receiving side of the Golgi apparatus is called the cis face; the opposite side is the trans face. Transport vesicles from the ER fuse with the cis face and empty their contents into the lumen of the Golgi apparatus. As the proteins and lipids travel through the Golgi, they are further modified so they can be sorted. This often involves adding short chains of sugar molecules 4.4 The Endomembrane System and Proteins Learning Objectives You should now be able to do the following: List the components of the endomembrane system Recognize the relationship between the endomembrane system and its functions 4.5 The Cytoskeleton Learning Objectives By the end of this section, you will be able to do the following: Describe the cytoskeleton Compare the roles of microfilaments, intermediate filaments, and microtubules Compare and contrast cilia and flagella Summarize the differences among the components of prokaryotic cells, animal cells, and plant cells  The Cytoskeleton The cytoskeleton is a network of protein fibers with several functions – It helps maintain the shape of the cell; – Holds some organelles in specific positions – Allows movement of cytoplasm and vesicles within the cell – Enables cells within multicellular organisms to move Three Components of Cytoskeleton Microfilaments Intermediate filaments Microtubules Microfilament Microtubule Intermediate filament These components have different sizes and different functions Wikimedia commons  Microfilaments Involved in movement – Whole cell or internal parts Determine & stabilize shape Made from actin monomers  Intermediate Filaments Tough, flexible fibers assembled from protein subunits Provide mechanical strength and help stabilize cell shape  Microtubules Form rigid internal skeleton for some cells Provide framework for motor proteins to move structures within cell Made of tubulin dimers – 13 chains of dimers surround central cavity of microtubule  Cilia & Flagella Ultrastructure – 9+2 array of microtubules 9 doublets on outside 2 unfused in center Spokes connect doublets to middle Cilia shorter and more numerous 4.5 The Cytoskeleton Learning Objectives You should now be able to do the following: Describe the cytoskeleton Compare the roles of microfilaments, intermediate filaments, and microtubules Compare and contrast cilia and flagella Summarize the differences among the components of prokaryotic cells, animal cells, and plant cells 4.6 Connections between cells and Cellular activities Learning Objectives By the end of this section, you will be able to do the following: Describe the extracellular matrix List examples of the ways that plant cells and animal cells communicate with adjacent cells Summarize the roles of tight junctions, desmosomes, gap junctions, and plasmodesmata  Extracellular Structures Plant cell wall – Support – Barrier to infection – Plasmodesmata connect cells Extracellular matrix in animals – 3 components Collagens & other fibrous proteins Glycoproteins called proteoglycans Linking proteins  Tight Junctions Tight Junctions are watertight seals between animal cells that prevent materials from leaking between cells These are found in epithelial cells that line internal organs and cavities.  Desmosomes Desmosomes are short proteins (cadherins) in the plasma membrane that act as spot welds These join adjacent cells in tissues that stretch (e.g. heart, lungs, muscles) Only present animals  Intercellular Junctions Intercellular junctions provide direct channels of communication between cells Plants and animals do this differently  Plasmodesmata Plasmodesmata are channels that pass between cell walls in plants to connect cytoplasm and allow materials to move from cell to cell (singular: plasmodesma plural: plasmodesmata) Gap Junctions connect animal cells – Gap junctions are found in animals and resemble plasmodesmata because they form channels that allow ions, nutrients and other material to move between cells – They develop when 6 proteins (connexins) form an elongated doughnut-like structure (connexon) in the plasma membrane – When connexons of adjacent cells are aligned, it completes the channel (credit: modification of work by Mariana Ruiz Villareal) 4.6 Connections between cells and Cellular activities Learning Objectives You should now be able to do the following: Describe the extracellular matrix List examples of the ways that plant cells and animal cells communicate with adjacent cells Summarize the roles of tight junctions, desmosomes, gap junctions, and plasmodesmata