How Cells Are Put Together Chapter 4

Smallest unit of life Can survive on its own or has potential to do so Is highly organized for metabolism Senses and responds to environment Has potential to reproduce Smallest unit of life Can survive on its own or has potential to do so Is highly organized for metabolism Senses and responds to environment Has potential to reproduce The Cell

Structure of Cells All start out life with: Plasma membrane Region where DNA is stored Cytoplasm All start out life with: Plasma membrane Region where DNA is stored Cytoplasm Two types: Prokaryotic Eukaryotic

Why Are Cells So Small? Surface-to-volume ratio The bigger a cell is, the less surface area there is per unit volume Above a certain size, material cannot be moved in or out of cell fast enough Surface-to-volume ratio The bigger a cell is, the less surface area there is per unit volume Above a certain size, material cannot be moved in or out of cell fast enough

Surface-to-Volume Ratio

Mid 1600s - Robert Hooke observed and described cells in cork Late 1600s - Antony van Leeuwenhoek observed sperm, microorganisms 1820s - Robert Brown observed and named nucleus in plant cells Mid 1600s - Robert Hooke observed and described cells in cork Late 1600s - Antony van Leeuwenhoek observed sperm, microorganisms 1820s - Robert Brown observed and named nucleus in plant cells Early Discoveries

Cell Theory 1) Every organism is composed of one or more cells 2) Cell is smallest unit having properties of life 3) Continuity of life arises from growth and division of single cells 1) Every organism is composed of one or more cells 2) Cell is smallest unit having properties of life 3) Continuity of life arises from growth and division of single cells

Create detailed images of something that is otherwise too small to see Light microscopes Simple or compound Electron microscopes Transmission EM or Scanning EM Create detailed images of something that is otherwise too small to see Light microscopes Simple or compound Electron microscopes Transmission EM or Scanning EM Microscopes

Limitations of Light Microscopy Wavelengths of light are nm If a structure is less than one-half of a wavelength long, it will not be visible Light microscopes can resolve objects down to about 200 nm in size Wavelengths of light are nm If a structure is less than one-half of a wavelength long, it will not be visible Light microscopes can resolve objects down to about 200 nm in size

Electron Microscopy Uses streams of accelerated electrons rather than light Electrons are focused by magnets rather than glass lenses Can resolve structures down to 0.5 nm Uses streams of accelerated electrons rather than light Electrons are focused by magnets rather than glass lenses Can resolve structures down to 0.5 nm

Electron Microscope incoming electron beam condenser lens (focuses a beam of electrons onto specimen) specimen objective lens intermediate lens projector lens viewing screen (or photographic film)

Main component of cell membranes Gives the membrane its fluid properties Two layers of phospholipids Main component of cell membranes Gives the membrane its fluid properties Two layers of phospholipids Lipid Bilayer

Fluid Mosaic Model Membrane is a mosaic of Phospholipids Glycolipids Sterols Proteins Most phospholipids and some proteins can drift through membrane Membrane is a mosaic of Phospholipids Glycolipids Sterols Proteins Most phospholipids and some proteins can drift through membrane

Membrane Proteins Adhesion proteins Communication proteins Receptor proteins Recognition proteins Adhesion proteins Communication proteins Receptor proteins Recognition proteins

Archaea and eubacteria DNA is not enclosed in nucleus Generally the smallest, simplest cells No organelles Archaea and eubacteria DNA is not enclosed in nucleus Generally the smallest, simplest cells No organelles Prokaryotic Cells

Prokaryotic Structure bacterial flagellum pilus plasma membrane DNA in nucleoid region cytoplasm, with ribosomes Most prokaryotic cells have a cell wall outside the plasma membrane, and many have a thick, jellylike capsule around the wall. bacterial flagellum

Eukaryotic Cells Have a nucleus and other organelles Eukaryotic organisms Plants Animals Protistans Fungi Have a nucleus and other organelles Eukaryotic organisms Plants Animals Protistans Fungi

Keeps the DNA molecules of eukaryotic cells separated from metabolic machinery of cytoplasm Makes it easier to organize DNA and to copy it before parent cells divide into daughter cells Keeps the DNA molecules of eukaryotic cells separated from metabolic machinery of cytoplasm Makes it easier to organize DNA and to copy it before parent cells divide into daughter cells Functions of Nucleus

Components of Nucleus Nuclear envelope Nucleoplasm Nucleolus Chromatin

Cell’s collection of DNA and associated proteins Chromosome is one DNA molecule and its associated proteins Appearance changes as cell divides Cell’s collection of DNA and associated proteins Chromosome is one DNA molecule and its associated proteins Appearance changes as cell divides

Nuclear Envelope Two outer membranes (lipid bilayers) Innermost surface has DNA attachment sites Pores span bilayer Two outer membranes (lipid bilayers) Innermost surface has DNA attachment sites Pores span bilayer one of two lipid bilayers (facing nucleoplasm) NUCLEAR ENVELOPE one of two lipid bilayers (facing nucleoplasm) nuclear pore (protein complex that spans both lipid bilayers)

Nucleolus Dense mass of material in nucleus May be one or more Cluster of DNA and proteins Materials from which ribosomal subunits are built Subunits must pass through nuclear pores to reach cytoplasm Dense mass of material in nucleus May be one or more Cluster of DNA and proteins Materials from which ribosomal subunits are built Subunits must pass through nuclear pores to reach cytoplasm

Group of related organelles in which lipids are assembled and new polypeptide chains are modified Products are sorted and shipped to various destinations Group of related organelles in which lipids are assembled and new polypeptide chains are modified Products are sorted and shipped to various destinations Endomembrane System

Components of Endomembrane System Endoplasmic reticulum Golgi bodies Vesicles Endoplasmic reticulum Golgi bodies Vesicles

Endoplasmic Reticulum In animal cells, continuous with nuclear membrane Extends throughout cytoplasm Two regions: rough and smooth In animal cells, continuous with nuclear membrane Extends throughout cytoplasm Two regions: rough and smooth

Rough ER Arranged into flattened sacs Ribosomes on surface give it a rough appearance Some polypeptide chains enter rough ER and are modified Cells that specialize in secreting proteins have lots of rough ER Arranged into flattened sacs Ribosomes on surface give it a rough appearance Some polypeptide chains enter rough ER and are modified Cells that specialize in secreting proteins have lots of rough ER

Smooth ER A series of interconnected tubules No ribosomes on surface Lipids assembled inside tubules Smooth ER of liver inactivates wastes, drugs Sarcoplasmic reticulum of muscle is a specialized form A series of interconnected tubules No ribosomes on surface Lipids assembled inside tubules Smooth ER of liver inactivates wastes, drugs Sarcoplasmic reticulum of muscle is a specialized form

Golgi Bodies Put finishing touches on proteins and lipids that arrive from ER Package finished material for shipment to final destinations Material arrives and leaves in vesicles Put finishing touches on proteins and lipids that arrive from ER Package finished material for shipment to final destinations Material arrives and leaves in vesicles

Vesicles Membranous sacs that move through the cytoplasm Lysosomes Peroxisomes Membranous sacs that move through the cytoplasm Lysosomes Peroxisomes

Central Vacuole Fluid-filled organelle Stores amino acids, sugars, wastes As cell grows, expansion of vacuole as a result of fluid pressure forces cell wall to expand In mature cell, central vacuole takes up percent of cell interior Fluid-filled organelle Stores amino acids, sugars, wastes As cell grows, expansion of vacuole as a result of fluid pressure forces cell wall to expand In mature cell, central vacuole takes up percent of cell interior

ATP-producing powerhouses Double-membrane system Carry out the most efficient energy-releasing reactions These reactions require oxygen ATP-producing powerhouses Double-membrane system Carry out the most efficient energy-releasing reactions These reactions require oxygen Mitochondria

Mitochondrial Structure Outer membrane faces cytoplasm Inner membrane folds back on itself Membranes form two distinct compartments ATP-making machinery is embedded in the inner mitochondrial membrane Outer membrane faces cytoplasm Inner membrane folds back on itself Membranes form two distinct compartments ATP-making machinery is embedded in the inner mitochondrial membrane

Chloroplasts Convert sunlight energy to ATP through photosynthesis

Structure of a Chloroplast Two outer membranes around semifluid interior (stroma) – bathes inner membrane Often, this single membrane is folded back on itself as a series of stacked, flattened disks Each stack is called a thylakoid, which contains chlorophylls and other substances involved in photosynthesis Two outer membranes around semifluid interior (stroma) – bathes inner membrane Often, this single membrane is folded back on itself as a series of stacked, flattened disks Each stack is called a thylakoid, which contains chlorophylls and other substances involved in photosynthesis

Like Bacteria? Both mitochondria and chloroplasts resemble bacteria Have own DNA, RNA, and ribosomes Both mitochondria and chloroplasts resemble bacteria Have own DNA, RNA, and ribosomes

Plant Cell Features

Animal Cell Features

Present in all eukaryotic cells Basis for cell shape and internal organization Allows organelle movement within cells and, in some cases, cell motility Present in all eukaryotic cells Basis for cell shape and internal organization Allows organelle movement within cells and, in some cases, cell motility Cytoskeleton

Cytoskeletal Elements microtubulemicrofilament intermediate filament

Microtubules Largest elements Composed of the protein tubulin Arise from microtubule organizing centers (MTOCs) Polar and dynamic Involved in shape, motility, cell division Largest elements Composed of the protein tubulin Arise from microtubule organizing centers (MTOCs) Polar and dynamic Involved in shape, motility, cell division

Microfilaments Thinnest cytoskeletal elements Composed of the protein actin Polar and dynamic Take part in movement, formation and maintenance of cell shape Thinnest cytoskeletal elements Composed of the protein actin Polar and dynamic Take part in movement, formation and maintenance of cell shape

Accessory Proteins Attach to tubulin and actin Motor proteins Crosslinking proteins Attach to tubulin and actin Motor proteins Crosslinking proteins

Intermediate Filaments Present only in animal cells of certain tissues Most stable cytoskeletal elements Six known groups Desmins, vimentins, lamins, etc. Different cell types usually have 1-2 different kinds Present only in animal cells of certain tissues Most stable cytoskeletal elements Six known groups Desmins, vimentins, lamins, etc. Different cell types usually have 1-2 different kinds

Length of microtubules or microfilaments can change Parallel rows of microtubules or microfilaments actively slide in a specific direction Microtubules or microfilaments can shunt organelles to different parts of cell Length of microtubules or microfilaments can change Parallel rows of microtubules or microfilaments actively slide in a specific direction Microtubules or microfilaments can shunt organelles to different parts of cell Mechanisms of Movement

Flagella and Cilia Structures for cell motility internal structure Structures for cell motility internal structure

False Feet Some free-living cells, such as amoebas, form pseudopods (“false feet”) These temporary, irregular lobes project from the cell and function in locomotion and prey capture Pseudopods move as microfilaments elongate inside them – motor proteins attached to the microfilaments drag the plasma membrane with them Some free-living cells, such as amoebas, form pseudopods (“false feet”) These temporary, irregular lobes project from the cell and function in locomotion and prey capture Pseudopods move as microfilaments elongate inside them – motor proteins attached to the microfilaments drag the plasma membrane with them

Structural component that wraps around the plasma membrane Occurs in plants, some fungi, some protistans Structural component that wraps around the plasma membrane Occurs in plants, some fungi, some protistans Cell Wall Primary cell wall of a young plant Plasma membrane

Plant Cell Walls Primary cell wall Secondary cell wall (3 layers)

Plant Cuticle Cell secretions and waxes accumulate at plant cell surface Semi-transparent Restricts water loss Cell secretions and waxes accumulate at plant cell surface Semi-transparent Restricts water loss

Matrixes between Animal Cells Animal cells have no cell walls Some are surrounded by a matrix of cell secretions and other material Animal cells have no cell walls Some are surrounded by a matrix of cell secretions and other material

Cell Junctions Plants Plasmodesmata Animals Tight junctions Adhering junctions Gap junctions Plants Plasmodesmata Animals Tight junctions Adhering junctions Gap junctions plasmodesma

Animal Cell Junctions