Chapter 4 A Tour of the Cell

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Transcript Chapter 4 A Tour of the Cell

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
Prokaryotic cells are older than eukaryotic cells.
• Prokaryotes appeared about 3.5 billion years ago.
• Eukaryotes appeared about 2.1 billion years ago.
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
• Only eukaryotic cells have organelles, membranebound 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
• 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
• hydrophobic
– Phosphate group in 3rd
• Charged, hydrophilic
• Phopholipid bilayer
– 2-layered membrane
– Proteins embedded in
• 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
– Flesh eating disease!!
Cell Surfaces
• Plant cells have rigid cell wall surrounding plasma
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
Cell Surfaces
• Animal cells lack cell wall
– 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 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
• Responsible for protein synthesis
• In eukaryotic cells, ribosomes make in nucleus
and transported into cytoplasm
– Suspended in fluid making proteins that remain in
– 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
• As ribosomes move along mRNA, genetic
message translated into protein with specific
amino acid sequence.
How DNA Directs Protein Production
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
Endoplasmic Reticulum (ER)
• Main functioning facility in cell
• Rough ER
– Ribosomes stud the surface
– Produce membrane and secretory proteins (i.e. salivary
– 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
• Receiving dock and shipping dock
• Modifications by enzymes as products move
from receiving to shipping
– Phosphate groups added as tags for different
The Golgi Apparatus
• Sac of digestive enzymes (animal cells)
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
• Sacs that bud from ER, Golgi or plasma
• 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
Review of Endomembrane System
Chloroplasts and Mitochondria
• Energy Conversion
• Cellular power stations
• Photosynthetic cells of plants and algae
• 3 compartments
– Space between membranes that surround
– Stroma: thick fluid
– Network of disks and tubes
• Grana: interconnected stacks of disks
• Solar power pack
• 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
The Cytoskeleton
• Network of fibers extending throughout
• 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
– 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