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Chapter 4 Cell Structure and Function
Ribosome (attached) Nucleolus Ribosome (free) Nucleus Cell Membrane Nuclear envelope Mitochondrion Smooth endoplasmic reticulum Rough endoplasmic reticulum Centrioles Golgi apparatus
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A CELL is . . . made of MOLECULES
ATOMS MOLECULES ORGANELLES _______ ___________ ___________
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WHICH IS BIGGER? _________ > _____________ > ___________
Plant cell Animal cell bacteria _________ > _____________ > ___________
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Note The shapes shown on the last slide are merely a generic version of a plant, animal, and bacteria cell. In other words, not all plants are shaped like a box and animal cells circular That is simply done to show that plants have cell walls and animal cells do not Every type of cell is shaped a particular way to fit whatever its function may be
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ALL LIVING THINGS ARE MADE OF CELLS
PROKARYOTES Lack nucleus Lack membrane bound organelles EUKARYOTES Have nucleus Have membrane bound organelles Bacterial Cell
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All cells (both prokaryotic and eukaryotic) have several basic features in common
Plasma (cell) membrane Chromosomes which carry genes made of DNA (although the shape of eukaryotic chromosomes and a prokaryotic chromosome are different) Cytoplasm Cytoskeleton Ribosomes that make proteins (although the shape of eukaryotic ribosomes and prokaryotic ribosomes are different)
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1. CELL MEMBRANE (also called plasma membrane)
Made mainly of phospholipids & proteins Controls what enters and leaves the cell Outside of cell Inside (cytoplasm) Cell membrane Proteins Protein channel Lipid bilayer Carbohydrate chains
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Cell membrane continued -PHOSPHOLIPID
Phospholipid has 2 main regions: Head negative charge, hydrophilic 2 fatty acid Tails nonpolar, hydrophobic HYDROPHILIC HYDROPHOBIC
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Cell membrane continued - PHOSPHOLIPID BILAYER
They form a two-layered sheet called the phospholipid bilayer. Hydrophilic heads face out Hydrophobic tails tucked inward. Proteins are embedded on the membrane, or attached to the surface.
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Cell membrane continued
Proteins are embedded on the membrane, or attached to the surface. Proteins that stick on the surface = PERIPHERAL (either inside or outside of cell) Proteins that stick INTO membrane = Integral (can go part way in or all the way through)
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Cell membrane continued - Permeability
Nonpolar molecules such as O2 and CO2 can easily pass through the hydrophobic interior. Proteins in the membrane form channels that allow specific molecules to cross.
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Cell membrane continued - GLYCOPROTEINS
Recognize “self” GLYCOPROTEINS are PROTEINS with carbohydrates attached. Play a role in cell-cell interactions.
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Cell membrane continued - TRANSPORT PROTEINS help move substances across the cell membrane
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Cell membranes MOVE! Molecules in cell membranes are
constantly moving and changing
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Cell membrane continued - WHAT DOES IT DO?
Acts as a boundary Controls what enters and leaves cell
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2. Chromosomes - Genetic material (DNA)
Chromatin – thin fibers of DNA and proteins that look like a diffuse mass. As the cell prepares to divide, the DNA is copied and the chromatin coils up (becoming visible with a light microscope) into the structure we know as chromosomes.
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3. CYTOPLASM (Between nucleus and cell membrane)
Organelles suspended in gel-like goo ORGANELLE- small structure with a specific function (job)
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4. CYTOSKELETON Helps cell maintain shape Help move organelles around
Network of protein fibers, found throughout the cytoplasm. Three main types of fibers make up the cytoskeleton: Microfilaments (the thinnest) Microtubules (the thickest) Intermediate filaments (in between) Helps cell maintain shape Help move organelles around
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Cytoskeleton continued -Microfilaments
Solid rods made of the protein actin, in a twisted double chain Supports the cell’s shape & involved in cell movement. Ex: Actin and another protein myosin interact to cause contraction of muscle cells. Actin subunit Microfilament
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Cytoskeleton continued - Microtubules
Straight hollow tubes made of the protein tubulin. Easily disassembled & subunits reused elsewhere. Give shape and support to the cell & acts as tracks along which organelles with motor proteins can move. Ex: lysosomes move along track to reach a food vacuole. Ex: guide chromosomes during cell division The main component of cilia & flagella Nucleus Tubulin subunit Microtubule
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Cytoskeleton continued - Intermediate filaments
Made of various proteins, and has a ropelike structure. Reinforce cell shape & anchors organelles. Ex: Nucleus is held in place by a cage of intermediate filaments. Ex: Our outer layer of skin consists of dead cells containing intermediate filaments made of keratin proteins. Nucleus Intermediate filament
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Characteristics of prokaryotic cells that are not found in eukaryotic cells
Bacterial chromosome – present as a single loop of DNA (eukaryotic chromosomes come in many pairs which we will discuss in detail later) Nucleoid – region where the prokaryotic cells DNA is located (not enclosed by a membrane like eukaryotic cells) Pili – attachment structures on the surface of some prokaryotes Cell wall – plants (which are eukaryotic cells) also have cell walls but they are made of a different structure Capsule – jellylike outer coating outside of cell wall Note: Flagella and cilia are also found in animal cells (not plants), but they are included here because the diagram shows them. Sperm have flagella, cells in your wind pipe have cilia, and so forth. Flagella (long tail like structure) and cilia (many hair like structures) used for locomotion (some types of eukaryotic cells do have flagella or cilia)
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Typical Prokaryotic cell
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Pili Nucleoid Ribosomes Plasma membrane Bacterial chromosome Cell wall
Fig. 4-3b Pili Nucleoid Ribosomes Plasma membrane Bacterial chromosome Cell wall Capsule Flagella
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Nucleoid The DNA of a prokaryotic cell is coiled into a region called the nucleoid. Unlike the eukaryotic nucleus, it has no membrane that surrounds the DNA. The DNA of a prokaryote is in a single circular loop. The DNA of eukaryotes (like you) are in chromosome form (we’ll discuss this next unit). Also, the ribosomes of prokaryotic cells are smaller. Antibiotics are designed to target (smaller) ribosomes of prokaryotic cells (bacteria), interrupting protein synthesis. Antibiotics do not harm eukaryotic cells.
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Cilia & Flagella Central microtubules Both consist of microtubules wrapped in an extension of the cell membrane. Ring of 9 microtubule “doublets” surrounds a central pair of microtubules. (called pattern) Plasma membrane Outer microtubule doublet
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Cilia – short numerous appendages that propel cell forward.
Found on cells lining the human windpipe, which sweeps mucus & trapped debris out of our lungs. Cilia
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Flagella – longer, and limited to one or a few per cell.
Sperm have flagella for movement. Flagellum Bacteria
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How did the first eukaryotic cells form?
ENDOSYMBIOSIS
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Endosymbiosis Mitochondria & chloroplasts were formerly small prokaryotes that began living within larger cells. May have occurred as undigested prey or internal parasites. Forming symbiotic relationship. Host cell uses nutrients released from photosynthetic endosymbionts. Endosymbionts are provided protection by host cell. Over time, they would become more interdependent, eventually becoming a single organism.
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Evidence of Endosymbiosis
Mitochondria & chloroplasts both contain their own DNA & ribosomes. Their ribosomes are more similar to prokaryotic ribosomes. Both reproduce by a splitting process similar to that of prokaryotes. Both are surrounded by two membranes.
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Mitochondrion Engulfing of photosynthetic prokaryote Some cells
Fig. 4-16 Mitochondrion Engulfing of photosynthetic prokaryote Some cells Engulfing of aerobic prokaryote Chloroplast Host cell Mitochondrion Host cell
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Organelles that are unique amongst eukaryotes (basically plants and animals) but not present in prokaryotes (bacteria) Nucleus Nucleolus Endoplasmic reticulum Golgi Apparatus (also called golgi body) Mitochondria Peroxisome Vacuoles
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1. NUCLEUS Contains cell’s genetic material (DNA)
Controls cell’s activity by directing protein synthesis. Largest organelle in animal cells
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1. NUCLEUS Surrounded by NUCLEAR ENVELOPE
It is a double membrane perforated with protein lined pores. (also called NUCLEAR MEMBRANE)
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1. NUCLEUS NUCLEAR PORES Openings that control the flow of materials into and out of the nucleus
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2. NUCLEOLUS Dark spot in nucleus
Site where ribosomal RNA (rRNA) is synthesized according to the instructions of DNA. Proteins brought in through the nuclear pores are assembled with the rRNA to build a subunit of ribosomes. These subunits exit through the nuclear pores where they will be joined to form functional ribosomes. Large subunit Small subunit Diagram of a ribosome
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Another type of RNA The nucleus directs protein synthesis with messenger RNA (mRNA). mRNA is a short transcription (copy) of DNA that exits through the nuclear pores where it is translated by ribosomes into amino acid sequences of proteins.
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RIBOSOMES for eukaryotes can be found in several places
Can be attached to: Nucleus Rough ER OR Free in cytoplasm
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3. ENDOPLASMIC RETICULUM
Network of flattened sacs and tubules “endoplasmic” – within the cell “reticulum” – little net Two kinds: SMOOTH or ROUGH
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Smooth ER NO ribosomes attached Has enzymes for special tasks:
Example: Cells of ovaries & testes synthesize the steroid sex hormones. Enzymes synthesize lipids (oils, phospholipids, & steroids)
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Another example (pg.60) Liver cells help process drugs and other harmful substances. Cells exposed to drugs cause the amount of smooth ER (w/ detoxifying enzymes) to increase This increases the rate of detoxification. Causing increasing tolerance to the drug. Now, dose must be increased to be effective. Another complication is that enzymes often cannot distinguish among related drugs. So an increase in tolerance in one drug, may cause one in another drug. Ex: barbiturate use can decrease effectiveness of antibiotics.
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Another example (pg.60) In muscle cells, smooth ER membrane pumps calcium ions into the interior of the ER. When a nerve signal stimulates a muscle, calcium ions rush from the smooth ER into the cytoplasm….triggering a contraction of the cell.
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Rough ER Rough ER membrane enlarges.
Phospholipids made by enzymes of the ER are inserted into the membrane. Some of this membrane is passed onto other membranes in vesicles.
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Rough ER Ribosomes attached. (rough)
These ribosomes make proteins, which are inserted into the ER membrane, where they are modified and transported to other organelles. Example: Insulin. Secreted by cells in the pancreas. 4 Ribosome 1 3 2
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After leaving the ER, many transport vesicles travel to the Golgi apparatus…
from ER Golgi apparatus Rough ER
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4. GOLGI APPARATUS (BODY)
Discovered by Camillo Golgi with a light microscope. Confirmed later with an electron microscope. Flattened sacs stacked on top of each other. Sacs are NOT interconnected like ER. Number of Golgi stacks correlates with how active the cell is in secreting proteins. Electron micrograph
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GOLGI APPARATUS (BODY)
Molecular warehouse & finishing factory. Receives & modifies products from ER. One side is receiving dock for transport vesicles Other side is shipping dock giving off vesicles. “maturation model” entire sacs mature as they move from the receiving end to the shipping end, carrying and modifying their cargo as they go. Exiting vesicles move to the cell membrane for export form the cell.
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5. Mitochondrion Mitochondria (plural)
cellular respiration - converts food energy into a molecule energy. ATP (adenosine triphosphate). The main energy source for cellular work.
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Mitochondrion’s structure
Enclosed by 2 membranes. The inner membrane is highly folded, and contains proteins that make ATP. The folds (cristae) increase membrane surface area, enhancing ability to produce ATP. Has 2 internal compartments Internal membrane space – narrow region between inner and outer membrane. Mitochondrial matrix – contains the mitochondrial DNA, ribosomes, & enzymes.
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Found in plant & animal cells!
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MITOCHONDRIA You inherit your mitochondria from your mother!
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WHAT DOES IT DO? “Powerplant of cell” Converts glucose to ATP
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6. Peroxisome Vesicle that neutralizes dangerous oxygen compounds
contains catalase that breaks down H2O2 Detoxification of alcohol Also breaks down fatty acids to be used as fuel.
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Zellweger Syndrome Defective genes reduce or eliminate the presence of peroxisomes Results in build up of iron and copper in blood and tissue Symptoms include an enlarged liver; facial deformities, and neurological abnormalities such as mental retardation and seizures. Most infants do not survive past the first 6 months, and usually succumb to respiratory distress, gastrointestinal bleeding, or liver failure.
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7. VACUOLES Membrane sacs used for storage
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VACUOLES Largest structure in plant cells Small in animal cells
Storage space for WATER, salts, proteins (enzymes), carbohydrates, and waste Maintains internal pH Largest structure in plant cells Small in animal cells No vacuoles in bacteria cells
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Contractile vacuoles Paramecium (unicellular organism, protists)
Collect excess water from cell, and expels it to the outside of cell. Without vacuole, cell fluid would become too diluted to support life, & cell would eventually swell & burst. Contractile vacuoles Nucleus
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Food Vacuole capture and digestion of food particles
Fuse with lysosomes to digest food And release nutrients. phagocytosis - the ingestion of particulate matter
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Organelles found only in plant cells
Cell wall (prokaryotes also have cell walls but they’re made of different material. Animals do not have cell walls) Chloroplast Central Vacuole
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1. CELL WALL Supports and protects cell
Outside of cell membrane Made of carbohydrates & proteins Plant cell walls are mainly cellulose
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2. Chloroplasts Photosynthesizing organelles - Use energy from sunlight to make own food (glucose)
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Chloroplasts Has an inner and outer membrane.
Inside inner membrane is a thick fluid called stroma. Stroma contains the chloroplast DNA & ribosomes.
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Chloroplasts Thylakoids (a network of connected sacs) are stacked inside the chloroplast. The stacks of thylakoids are called grana Grana are the solar power packs – site where green chlorophyll molecules trap solar energy.
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3. Central vacuole Found in plant cells.
Can take up more than half the cells volume Holds large amounts of water, food & waste Plays an important role in plant structure. Vacuoles in flower petals contain pigments to attract insects!
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Organelles found only in animal cells (not in plants or prokaryotes)
Centrioles Lysosomes – basically the “recycling center” of the cell The most common hypothesis as to why plant cells do not need lysosomes is that they have a cell wall that would prevent the majority of material broken down by lysosomes in animal cells from entering plant cells
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1. Centrioles Appear during cell division to guide chromosomes apart
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Centrioles
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2. LYSOSOMES Membrane bound sacs that contain digestive enzymes. Made by rough ER & transferred to Golgi body. Serves as a recycling center. Damaged organelles are dismantled, releasing organic molecules for reuse. * Found in animal cells only!
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2. LYSOSOMES Protists engulf food particles into vacuoles…
White blood cells ingest bacteria into vacuoles… Lysosomes fuse with these vacuoles and empties its digestive enzymes into them. Digestive enzymes Lysosome Plasma membrane Digestion Food vacuole
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Lysosomal storage disease
Lack one or more lysosomal enzymes. Lysosomes become engorged with undigested material. Example: Tay-Sachs disease Lipid digesting enzyme is missing Brain cells become impaired by accumulation of lipids. A child with Tay-Sachs disease will die within a few years.
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Apoptosis Programmed cell death Lysosomes help digest unwanted cells
Cells in developing hands and feet creates the spaces between fingers & toes. Apoptosis Dead cell engulfed and digested by adjacent cell
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Apoptosis plays a role in:
Embryonic development Normal body cell maintenance Immune system responses Cancer AIDS infection Transplant rejection
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Cell to cell communication
The vast majority of eukaryotic organisms are multicellular In order to function properly, these cells must be able to communicate with one another and to transmit information back and forth
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Extracellular matrix (ECM) – Present only in animals
Helps hold cells together in tissues. Protects and supports the plasma membrane. Main component: glycoproteins (ex: collagen) Integers - membrane proteins that interconnects the ECM to the cytoskeleton.
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Glycoprotein complex with long polysaccharide Collagen fiber
Fig. 4-20 Glycoprotein complex with long polysaccharide EXTRACELLULAR FLUID Collagen fiber Connecting glycoprotein Integrin Plasma membrane Microfilaments CYTOPLASM
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Three types of cell junctions in animal cells
Tight junction – membranes of neighboring cells are very tightly pressed against each other. Prevent leakage of extracellular fluid Example: tissue lines the digestive tract, preventing the contents from leaking into surrounding tissues. Tight junctions
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Three types of cell junctions in animal cells
Anchoring junction – functions like rivets, fastening cells together into strong sheets. Common in tissue subject to stretching or mechanical stress. Skin & heart muscle Anchoring junction
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Three types of cell junctions in animal cells
Gap junctions – channels that allow small molecules to flow through protein lined pores between neighboring cells. Ex: flow of ions through gap junctions in the cells of heart muscle coordinates their contraction. Gap junctions
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Tight junctions Anchoring junction Gap junctions Plasma membranes
Fig. 4-21 Tight junctions Anchoring junction Gap junctions Plasma membranes of adjacent cells Extracellular matrix
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Plasmodesmata – Present only in plant cells
Channels between adjacent plant cells, form a circulatory and communication system connecting the cells in plant tissue. Cell membrane & cytoplasm extend through the plasmodesmata, so water and molecules can pass cell to cell.
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Walls of two adjacent plant cells Vacuole Plasmodesmata
Fig. 4-22 Walls of two adjacent plant cells Vacuole Plasmodesmata Primary cell wall Secondary cell wall Cytoplasm Plasma membrane
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DIFFERENCES IN ANIMAL CELLS, PLANT CELLS, AND BACTERIA ANIMAL CELL
Eukaryotes Prokaryotes Cell membrane Nuclear membrane NO nuclear membrane NO cell wall Cell wall made of CELLULOSE Cell wall made of PEPTIDOGLYCAN Has ribosomes DNA in multiple chromosomes DNA in multiple chromosomes DNA is a single circular ring CYTOSKELETON Small vacuoles Really big vacuole NO vacuoles Has lysosomes NO lysosomes Has centrioles NO centrioles Has mitochondria No mitochondria NO chloroplasts Chloroplasts SMALLER SMALL SMALLEST
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USE WORDS FROM THE WORD BANKS TO COMPLETE THE VENN DIAGRAM COMPARISON
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NUCLEUS: Rough endoplasmic reticulum Nuclear envelope Chromosome
Fig. 4-4b NUCLEUS: Rough endoplasmic reticulum Nuclear envelope Chromosome Ribosomes Nucleolus Smooth endoplasmic reticulum Golgi apparatus CYTOSKELETON: Central vacuole Microtubule Chloroplast Intermediate filament Cell wall Plasmodesmata Microfilament Mitochondrion Peroxisome Plasma membrane Cell wall of adjacent cell
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NUCLEUS: Nuclear envelope Chromosomes Smooth endoplasmic reticulum
Fig. 4-4a NUCLEUS: Nuclear envelope Chromosomes Smooth endoplasmic reticulum Nucleolus Rough endoplasmic reticulum Lysosome Centriole Ribosomes Peroxisome Golgi apparatus CYTOSKELETON: Microtubule Plasma membrane Intermediate filament Mitochondrion Microfilament
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Fig. 4-UN3 a. l. b. c. k. j. i. h. d. g. e. f.
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