Chapter 4 A Tour of the Cell SC 101 General Biology Essential Biology CM Lamberty

The Microscopic World of Cells Cells are marvels of complexity Trillions of cell in human body Many specialized types Main tool for exploration--Microscope

Microscopes as Windows on the World of Cells Light Microscope (LM) Visible light projected through specimen Lenses enlarge the image and project to eye View living cells Magnification Increase in size, depends on lens Resolving Power Clarity of magnified image Electron Microscope (EM) beam of electrons Scanning Electron Microscope (SEM) View cell surfaces Transmission Electron Microscope (TEM) View internal structures

Microscopes as Windows on the World of Cells

Microscopes as Windows on the World of Cells

The 2 Major Categories of Cells The countless cells on earth fall into two categories: Prokaryotic cells — Bacteria and Archaea Eukaryotic cells — plants, fungi, and animals All cells have several basic features. They are all bound by a thin plasma membrane. All cells have DNA and ribosomes, tiny structures that build proteins

The 2 Major Categories of Cells Prokaryotic and eukaryotic cells have important differences. Prokaryotic cells are older than eukaryotic cells. Prokaryotes appeared about 3.5 billion years ago. Eukaryotes appeared about 2.1 billion years ago. Prokaryotes Are smaller than eukaryotic cells Lack internal structures surrounded by membranes Lack a nucleus Have a rigid cell wall

Idealized Prokaryotic Cell

The 2 Major Categories of Cells Eukaryotes Only eukaryotic cells have organelles, membrane-bound structures that perform specific functions. The most important organelle is the nucleus, which houses most of a eukaryotic cell’s DNA.

Idealized Eukaryotic Cell

Overview of Eukaryotic Cells Eukaryotic cells are fundamentally similar. The region between the nucleus and plasma membrane is the cytoplasm. The cytoplasm consists of various organelles suspended in fluid. Unlike animal cells, plant cells have Protective cell walls Chloroplasts, which convert light energy to the chemical energy of food

Membrane Structure Separates living cell from nonliving surroundings Regulates traffic of chemicals in and out of cell Key to how it works is the structure

Plasma Membrane: Lipids & Proteins Phospholipids Related to dietary fats Only 2 fatty acid tails not 3 hydrophobic Phosphate group in 3rd position Charged, hydrophilic Phopholipid bilayer 2-layered membrane Proteins embedded in bilayer Regulate traffic

Plasma Membrane: Lipids & Proteins Fluid Mosaic Not static (fluid) Diverse proteins (mosaic) Phospholipids and proteins free to drift about in the plane of the membrane Illness can result if membrane is compromised Superbugs: staphylococcus aureus MRSA Flesh eating disease!!

Cell Surfaces Plant cells have rigid cell wall surrounding plasma membrane Made of cellulose Protect the cells Maintain cell shapes Keep cells from absorbing too much water Cells connected via channels through cell walls Join cytoplasm of each cell to neighbor Allow water and small molecules to move between cells

Cell Surfaces Animal cells lack cell wall Cells junctions Extracellular matrix Sticky coating to hold cells together Protects and supports cells Cells junctions Connect cells togther Allow cells in tissue to function in coordinated way

Genetic Control of Cell Nucleus chief of the cell Genes store information necessary to produce proteins Proteins do most of the work of the cell

Structure and Function of Nucleus Nuclear Envelope Double membrane that surrounds nucleus Similar in structure to plasma membrane Pores allow transfer of materials Nucleolus Prominent structure Where ribosomes are made Chromatin Fibers formed from long DNA and associated proteins Chromosome One chromatin fiber

The nucleus

DNA, chromatin and chromosomes

Ribosomes Responsible for protein synthesis In eukaryotic cells, ribosomes make in nucleus and transported into cytoplasm Suspended in fluid making proteins that remain in fluid Attached to outside of endoplasmic reticulum, making proteins incorporated into membranes or secreted by cell

How DNA Directs Protein Production DNA programs protein production in cytoplasm via mRNA mRNA exits through pores in nuclear envelope, travels to cytoplasm, and binds to ribosomes As ribosomes move along mRNA, genetic message translated into protein with specific amino acid sequence.

How DNA Directs Protein Production DNA RNA Protein

The Endomembrane System Cytoplasm of eukaryotic cells partitioned by organelle membranes Some are connected Directly by membranes Indirectly by transfer of membrane segments Together form endomembrane system Includes nuclear envelope, endoplasmic reticulum, Golgi apparatus, lysosomes and vacuoles

Endoplasmic Reticulum (ER) Main functioning facility in cell Rough ER Ribosomes stud the surface Produce membrane and secretory proteins (i.e. salivary glands) Products transferred via transport vesicles Smooth ER Lacks ribosomes on surface Synthesis of lipids (steroids) Helps liver detoxify drugs

Endoplasmic Reticulum (ER)

The Golgi Apparatus Refinery, warehouse and shipping center Products made in ER reach Golgi in transport vehicles Receiving dock and shipping dock Modifications by enzymes as products move from receiving to shipping Phosphate groups added as tags for different destinations

The Golgi Apparatus

Lysosomes Sac of digestive enzymes (animal cells) Proteins Polysaccharides Fats Nucleic acids Develop from vesicles budding from Golgi Food vacuoles fuse with lysosomes, exposing food to enzymes for digestion Small molecules from digestion leave the lysosome and nourish the cell. Breakdown damaged organelles Sculpturing feature Digest webbing between fingers and toes

Lysosomes

Vacuoles Sacs that bud from ER, Golgi or plasma membranes Variety of size and function Contractile vacuoles of protists pump out excess water in the cell. Central vacuoles of plants Store nutrients Absorb water May contain pigments or poisons

Vacuoles

Review of Endomembrane System

Chloroplasts and Mitochondria Energy Conversion Cellular power stations

Chloroplasts Photosynthetic cells of plants and algae 3 compartments Space between membranes that surround chloroplast Stroma: thick fluid Network of disks and tubes Grana: interconnected stacks of disks Solar power pack

Chloroplasts

Mitochondria Site of cellular respiration Harvest E from food MQ and converts to ATP Found in all eukaryotic cells Structure Enveloped by 2 membranes filled with matrix Inner membrane has several infoldings (cristae) Contain DNA that encodes their own protein

Mitochondria

The Cytoskeleton Network of fibers extending throughout cytoplasm Skeleton and muscles Support and movement

Maintaining Cell Shape Series of fibers Microtubules Straight hollow tubes composed of proteins Guide movement of chromosomes when cells divide Intermediate filaments and Microfilaments Both thinner and solid Anchorage and reinforcement for organelles Dynamic cytoskeleton (amoeboid movements)

Maintaining Cell Shape

Cilia and Flagella Mobile appendages Aid in movement Flagella Cilia Generally occur singly Propel cell Undulating whiplike motion Cilia Shorter and more numerous than flagella Promote movement by back and forth motion Some function to move fluid over tissue surfaces

Cilia and Flagella