Chapter 4 - Cell Structure and Function

Robert Hooke-First person to see cells, he coined the term "cell" for the great many boxes he saw under the microscopeAnton van Leeuwenhoek saw first living single celled organisms (animalcules)

The Cell Theory

( Shwann | Shleiden | Virchow )

1. Every living organism is made of one or more cells2. Cells are the functional unit of multicellular organisms3. Cells arise from pre-existing cells

Cell Size

atoms --> DNA --> virus --> bacteria (Prokaryotes) -->mitochondria--> Eukaryotic cells

Cells must remain small in size due to the ratio of surface area and volumeAs the cell increases in size, its surface area becomes too small to support its internal structures. Oxygen and other important substances cannot diffuse fast enough. Cells that get too large, may divide.

All Cells Have Three Basic Features: Cell Membrane, Genetic Material, Cytoplasm

1. Plasma Membrane (aka Cell Membrane)Isolates cytoplasm from external environment2. regulates flow or material into and out of the cell3. allows interaction with other cells2. Genetic Material1. provides cellular "blueprint" that controls the functions of the cell2. In the form of DNA (Deoxyribonucleic acid)3. DNA is universal for all cells, an all living things - evidence of common ancestry4. Chromatin is the complex of proteins and DNA, it condenses into chromosomes before cell division3. Cytoplasm (aka cyosol)1. inside plasma membrane2. contains water, salts, and other chemicals3. organelles float within this jelly-like substance

Prokaryote vs Eukaryote CellsProkaryotes

no membrane bound nucleus, chromosomes grouped together in an area called the "nucleoid"

no membrane bound organelles

smaller than eukaryotes

have cell wall and cell membrane, some have a capsule on the outside

ribosomes make protein

consist of bacteria and archaebacteria

Appendages include: fimbriae, pili, flagella

Eukaryotes

has a membrane bound nucleus

has membrane bound organelles in cytoplasm

Organelles perform specific functions

much larger than prokaryotes

animals, plants, fungi, protists

Endosymbiosis theory:All organelles seem to share many properties with bacteria. Lynn Margulis proposed endosymbiont hypothesis: that organelles derived from ancient colonization of large bacteria (became the eucaryotic cell) by smaller bacteria (became the mitochondria, chloroplast, etc.) Symbiosis = living together.he Parts of the CellThe Nucleus--nuclear envelopecontainsnuclear poresfor some things to enter and exit (nucleoplasmwithin)--chromatinis DNA and proteins, when the cell begins to divide, chromatin condenses and formschromosomes--DNA remains in the nucleus, it sends instructions to the cytoplasm viamessenger RNA--RNA directs the synthesis of proteins onribosomesin the cytoplasm--Nucleolusassembles ribosomes within the nucleus, ribosomes contain the "tools" to construct proteins

Endoplasmic Reticulum-- Transport System(endoplasm means "within cytoplasm", reticulum means "little net"--divides cell into compartments--channels molecules through the cell's interior, like a little highwayRough ER--has ribosomes which give it its "rough" appearance--functions in protein synthesis--ER transports newly assembled proteins to the Golgi ApparatusSmooth ER--mostly contains enzymes that unction in lipid synthesis (such as hormones like estrogen and testosterone)

Golgi Apparatus -- Delivery System--flattened stacks of membranes--functions in collection, packaging and distribution of molecules made in the cell and used elsewhere-- front end (cis) faces the ER, and the back end (trans) faces the cell membrane --the folded stacks are called cisternae--unprocessed proteins enter the Golgi apparatus from ER proteins are packaged and exported near membrane

Jobs of the Golgi Apparatus (aka Golgi Complex)1. separates proteins according to their destinations2. modifies proteins (adds sugar and makes glycoproteins)3. packages materials intovesicleswhich are exported outside the cell -secretion

Lysosomes - Intracellular Digestion Centers--vesicles that are used to digest--contain high levels of degrading enzymes (to "lyse" means to dissolve)--recycle old and worn out cell parts--"suicide sac" -apoptosis--digest other particles taken in byphagocytosis--this "food" is stored in food vacuoles, the lysosomes fuse with the vacuoles and release digestive enzymes--found in animal cells

TAY-SACHS disease missing an enzyme of the lysosomes that breaks down a fatty substance. Over time this fat builds up in the brain and nervous tissue, smothering the cells. Results in degeneration and death.Ribosomes - Sites of Protein Synthesis--each is composed of two subunits, one large and one small--mRNA is "read" by the ribosomes and amino acids are assembled into proteins--ribosomes are manufactured by the nucleolus inside the nucleus--polyribosomes strings of ribosomes in the cytoplasm that work to make a protein

Other Organelles

--Peroxisomes result in hydrogen peroxide, broken down by catalase--Vacuole -- mainly storage or specific functions (contractile vacuole)-- Plant cells have aCENTRALVACUOLE - used for storage and help to maintain hydrostatic pressure

ENERGY RELATED ORGANELLESMitochondria - The Cell's Chemical Furnaces--contains its own DNA, support for Endosymbiosis Theory--singular is "mitochondrion"--2 membranes, one smooth outer membrane, and an inner membrane folded into layers calledcristae--Cristae has two compartments: thematrixand the intermembrane space--mitochondria divide before cell division, they are not synthesized like other cell parts--function to store energy for cell use. Energy is stored in the form ofATP- adenosine triphosphate

Chloroplasts - Where Photosynthesis Takes Place--only found in plant cells--has its own DNA, like mitochondrion--functions to convert light energy tocarbohydrates--carbohydrates then broken down in mitochondria to produce ATP--consists of grana, closed compartments that are stacked--thylakoidsare the individual disk shaped compartments that make up thegrana(stack of thylakoids)--stromais the fluid surrounded the thylakoids*Chloroplasts are a type ofplastidChromoplasts red, yellow and orange pigmentLeucoplasts colorless (potatoes)

Cytoskeleton - Support SystemMicrofilaments (now calledactin filaments) occur in bundles, form tracks within the cell for the movement of organelles, used to formpseudopods (ameba)Intermediate filaments - support membrane, cell to cell junctionsMicrotubules -(little pipe) regulated by theMTOC(microtubule organizing center), radiate from thecentrosome -form thespindleduring cell divisionCentrioles used during cell division to move and separate chromosomes, only found in animal cell

Related to MovementPseudopod extensions of the cell that allow for movement (ameba), depend on actin filamentsCilia(hair) &Flagella(whip)--function in movement-- 9+ 2 Arrangement of microtubules

Chapter 5 - Membrane Structure and Function

The Plasma Membrane

--the fluid mosaic model (S.J Singer)-- semi-permeable--fluid portion is a double layer of phospholipids, called the phospholipid bilayer

Jobs of the cell membrane

Isolate the cytoplasm from the external environment

Regulate the exchange of substances

Communicate with other cells

Identification

The Plasma Membrane is also called thePhospholipid bilayerPhospholipids contain a hydrophilic head and a nonpolar hydrophobic tail

Hydrogen bonds form between the phospholipid "heads" and the watery environment inside and outside of the cellHydrophobic interactions force the "tails" to face inwardPhospholipids are not bonded to each other, which makes the double layer fluid

Cholesterol embedded in the membrane makes it stronger and less fluid

Proteins embedded in membrane serve different functions

1. Channel Proteins - form small openings for molecules to difuse through2. Carrier Proteins- binding site on protein surface "grabs" certain molecules and pulls them into the cell3. Receptor Proteins - molecular triggers that set off cell responses (such as release of hormones or opening of channel proteins)4. Cell Recognition Proteins - ID tags, to idenitfy cells to the body's immune system5. Enzymatic Proteins - carry out metabolic reactions

Transport Across Membrane

The membrane is differentiallty permeable (also called semipermeable ) - which means

Passive Transport

Simple Diffusion - water, oxygen and other molecules move from areas of high concentration to areas of low concentration, down a concentration gradientFacilitation Diffusion - diffusion that is assisted by proteins (channel or carrier proteins)

Osmosis - diffusion of water. Salt SucksOsmosis affects the turgidity of cells, different solution can affect the cells internal water amounts

Contractiles Vacuoles are found in freshwater microorganisms - they pump out excess water

Turgor pressure occurs in plants cells as their central vacuoles fill with water.

Active Transport - involves moving molecules "uphill" against the concentration gradient, which requires energy

Endocytosis - taking substances into the cell (pinocytosis for water, phagocytosis for solids)Exocytosis - pushing substances out of the cell, such as the removal of wasteSodium-Potassium Pump - pumps out 3 sodiums for ever 2 potassium's taken in against gradient

Demo - Starch in the baggie, iodine in the beaker. What happens and why?Observation of elodea cells in salt water. What happens and why?

Modification of Cell Sufaces

Tight junctions are composed of protein fibers that seal adjacent cells to prevent leakage, something which can be useful in organs such as the bladder and the lining of the digestive tract. Tight junctions literally fuse the cells together forming a sheet of cells restricting molecules to one side of the sheet or the other.

Tight junctions can also partition the cells in which they are found. Certain membrane proteins can be restricted to one side of the junction, as well, since the tight junction prevents protein migration within the membrane.

Gap junctions are protein channels, called connexons, between adjacent cells that permit the transfer of small molecules, such as nutrient monomers, between the cells. They are common in brain cells, forming the synapse, in many glands, and in cells in the heart muscle that coordinate contraction for heartbeat. Gap junctions can be gated.

Desmosomes anchor adjacent cells together by making connections that work like staples or rivets that attach to components of the cytoskeleton. Many epithelial cells must adhere to adjacent membranes to prevent free passage or free movement, and to not break apart under stress. Desmosome filaments are composed of specialized glycoproteins proteins. Intermediate filaments of keratin in the desmosomes help strengthen the junction. Actin microfilaments can also attach to desmosomes, but have less strength

*Plants have plasmodesmata - channels between the cell wall that cytosol can pass through

Top of Form

Quiz: Cell Membrane and the Parts of the Cell

1. The door to your house is like the ___ of a cell membrane?phospholipid bilayergated channelreceptor proteinrecognition protein

2. The phospholipid bilayer of the cell membrane is like a(n):screen doorplate glass windowhot water heateroven

3. Facilitated diffusion ____ require energy and uses the help of ______does, transport proteinsdoes, cytoplasmdoes not, transport proteinsdoes not, sodium pumps

4. A semi permeable membrane is stretched across a chamber filled with water. The membrane is only permeable to water. 60 mg of salt is added to the left side of the chamber. Which of the following will happen?water will move toward the right sidesalt will move toward the right sidewater will move toward the left sidesalt will move toward the left side

5. The lipid bilayer keeps the inside of the cell membrane:bipolarprotein saturateddrywet

6. Which of the following could be found in BOTH the nucleus and the cytoplasmnucleolusribosomesRNAboth RNA & ribosomes

7. Amino acid chains built by the ribosomes then move to the:golgi apparatuslysosomeendoplasmic reticulummitochondria

8. Which of the following structures has a 9 + 2 arrangement?flagellaribosomemitochondriagolgi apparatus

9. The centriole is most like the:lysosomeflagellamitochondriachromatin

10. Which of the following is composed of a large and a small subunit?golgi apparatusendoplasmic reticulummitochondriaribosome

11. A cell that is missing lysosomes would have difficulty doing what?digesting foodstoring energypackaging proteinsmoving cytoplasm

12. Which of the following cell parts is described as a "fluid mosaic"?chloroplastvacuolecell membraneendoplasmic reticulum

13. Some cells take in large molecules through the process of:protein synthesisendocytosiscytoplasmic streamingATP

14. Which of the following organelles would NOT be found in a plant cell?chloroplastDNAfood vacuolecell membrane

Score =Correct answers:

Bottom of Form

Related Quizzes:Cell Quiz|Parts of the Cell|The Cell TheoryComparing Plant and Animal Cells

Check if present

Plant CellAnimal CellProkaryotesFunction (Sketch)

Plasma Membrane

Nucleus

Chromatin

Nucleolus

Lysosomes

Smooth Endoplasmic Reticulum

Rough Endoplasmic Reticulum

Golgi Apparatus

Mitochondria

Cytoskeleton

Centrioles

Flagella

Tight Junctions

Central Vacuole

Vacuole

Desmosomes

Plasmodesmata

Cell Wall

Chloroplasts

Additional Resources:Cell Label SheetCheck if present

Plant CellAnimal CellProkaryotesFunction

Plasma MembraneXXXBarrier, homeostasis

NucleusXXContains DNA

ChromatinXXXDNA and proteins, genetic code

NucleolusXXMakes ribosomes

LysosomesXXContains digestive enzymes

Smooth Endoplasmic ReticulumXXIntracellular transport

Rough Endoplasmic ReticulumXXIntracellular transport, mainly proteins

Golgi ApparatusXXPackaging proteins

MitochondriaXXProvides energy (ATP)

CytoskeletonXXXSupport within the cell

CentriolesXXMoves chromosomes during cell division

FlagellaXXXMovement, like a tail

Tight JunctionsXXHolds individual cells together

Central VacuoleXHolds water

VacuoleXXHolds water or enzymes

DesmosomesXXAnchors the cell to other cells

PlasmodesmataXChannels between the cell walls

Cell WallXXExtra support and protection

ChloroplastsXPhotosynthesis

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