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Cell Structure and Function Chapter 4 Biology 100. Discovery of the Cell. Robert Hooke used a simple kind of microscope to study slices of cork in 1664. He saw many cubicles fitting neatly together Hooke called these cells.

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Cell structure and function chapter 4 biology 100

Cell Structure and FunctionChapter 4Biology 100

Discovery of the cell
Discovery of the Cell

  • Robert Hooke used a simple kind of microscope to study slices of cork in 1664.

  • He saw many cubicles fitting neatly together

    • Hooke called these cells.

  • van Leeuwenhoek was the first to see living cells and later was first to see bacteria

Van Leeuwenhoek’s microscope

The cell theory
The Cell Theory

  • Schleiden and Schwann came up with the theory in the 1830’s

    • All living things are made of cells

  • Virchow added in 1855 to the cell theory

    • New cells are formed only from division of pre-existing cells, not spontaneous generation

Differences and similarities of cells
Differences and Similarities of Cells

  • All cells are surrounded by a plasma membrane (cell membrane) which is selectively permeable to materials.

  • Prokaryotes lack a true nucleus as well as internal membrane-bound organelles.

    • Bacteria

  • Eukaryotes have a true nucleus and have at least one membrane-bound organelle

    • Include plant, animal, fungi, protozoa and algae cells

Cell size
Cell Size

  • Prokaryotic cells can be 1-10 μm, while eukaryotic cells are 10-100 μm.

  • Some eukaryotic cells are quite large, like the yolk of a chicken egg

  • Two organelles found in eukaryotes, the mitochondrion and the chloroplast, are similar in size to most bacteria.

Cell size1
Cell Size

  • The ratio of surface area to cell volume limits cell size because it reflects the balance between supply rate and supply demand.

    • The surface area determines the rate at which materials diffuse into or out of the cell.

  • For a cell of a constant shape, for every time the surface area increases by L2, volume increases L3


  • Prokaryotes have no true nucleus or membrane-bound organelles, have a nucleoid region

  • Has a Cell Wall, and some may have a capsule, which encloses the cell wall

  • Forms of movement are the flagella and/or the pilli

  • Contains ribosomes where protein synthesis occurs


  • Bacteria cells have different shapes

    • Rod-shape

    • Spherical shape

    • Spiral


  • Eukaryotes, unlike prokaryotes, have a true, membrane-bound nucleus.

    • Contain a variety of organelles, specialized membrane-bound structures where cell processes occur

Endoplasmic reticulum
Endoplasmic Reticulum

  • Endoplasmic Reticulum (ER) is where proteins and lipids are synthesized

    • Large surface area

    • Rough ER is embedded with ribosomes

      • Ribosomes are nonmembranous organelles that help with synthesis of proteins

    • Smooth ER is where lipids are synthesized, detox

Golgi apparatus
Golgi Apparatus

  • Golgi Apparatus are smooth, flattened membranous sacs

    • Collects, packages and distributes molecules manufactured in the cell

    • Animals contain around 20 complexes, plants have hundreds.

Vesicles and vacuoles
Vesicles and Vacuoles

  • Tiny, membranous sacs known as vesicles deliver molecules to and from the Golgi Complex, vacuoles are larger structures that perform the same tasks

    • Some go from ER to the Golgi Complex

    • Some go to other organelles in cell

    • Others will go to plasma membrane and combine with it

      • May contain insulin, enzymes, etc. to go outside the cell

      • In plants, some vesicles have cellulose to make new cell wall material

    • Some vesicles contain enzymes to breakdown various molecules


Fig. 4.11, pg. 77.


  • A lysosome is a tiny vesicle that buds off the Golgi Apparatus and contains enzymes that break down macromolecules, for digestion and destruction

    • These enzymes function best at a pH of 5

      • Hydrogen ions are transported into lysosome to create this acidic environment

    • Will also destroy bacteria, viruses and fungi


  • A peroxisome is an organelle that has the enzyme, catalase, that breaks down hydrogen peroxide, H2O2

    • Breaks down fatty acids into 2 carbon fragments

    • n addition it includes enzymes which synthesize cholesterol and bile acids.

  • Is not formed in the Golgi apparatus

  • Aids chemical reactions, including the breakdown of fatty acids, synthesis of cholesterol and synthesis of lipid molecules


  • Ribosomes are constructed from two subunits, which are composed of ribosomal RNA and proteins.

  • Ribosomes synthesize polypeptides from free amino acids, according to the instructions on messenger RNA.

  • Ribosomes are like CD players, producing music (proteins) according to the instructions on the CD (mRNA).


  • The nucleus is surrounded by two membranes, the nuclear envelope

  • Protein complexes at nuclear pores regulate the entry of large macromolecules into and out of the nucleus

  • The nucleus contains most of the DNA in a cell.


  • The primary function of the nucleus is to transfer the information for the synthesis of proteins from DNA to RNA.

  • The nucleolus is a dense area within the nucleus with DNA fragments, ribosomal RNA, and proteins.

  • The nucleolus organizes the RNA and proteins into the ribosomal subunits.


  • Mitochondrion (singular) has two membranes

  • Outer membrane is relatively simple, but the inner membrane is highly folded, a structure called cristae

  • Cristae are rich in enzymes for electron transfer and ATP synthesis


  • The matrix is a fluid filled space inside the inner membrane

  • It contains soluble enzymes for aerobic cellular respiration.

  • The matrix also contains DNA (mtDNA), RNA, and ribosomes.


  • Known as the powerhouse of the cell

  • It converts the energy stored in organic molecules to forms usable to the cells, especially production of ATP

  • Food + O2 → CO2 +H20 + Energy (ATP)


  • Chloroplasts are also surrounded by two membranes.

  • The outer and inner membranes, and intermembrane space are barriers, but play no specific functional role in photosynthesis.

  • Inside the inner membrane is the stroma, an aqueous space.

  • Floating in the stroma are thylakoids, flat membranous sac.


  • The thylakoid membrane contains chlorophyll and other pigments, electron transfer molecules, and enzymes that trap the energy in sunlight - photosynthesis.

  • This energy is used to generate ATP and high energy electrons in the light-dependent phase of photosynthesis.

  • These molecules pass to the stroma where CO2 and H2O are converted into sugars.


  • The stroma also contains DNA (chDNA), RNA, and ribosomes.

  • In the stroma, DNA is transcribed to RNA and RNA is translated into some chloroplast proteins.


  • Intermediate filaments are semi-permanent components of the cytoskeleton.

  • Intermediate filaments are semi-permanent components of the cytoskeleton.

  • Intermediate filaments maintain cell shape and attach to proteins in the cell membrane


  • Microfilaments are built with the beadlike protein actin

  • During cell division, motor proteins pull actin filaments together, slicing the cytoplasm in half like string around a ball of dough.

  • In muscle cells, the motor protein myosin pulls together microfilaments during contraction.


  • Microtubules are small tubes that are built with the protein tubulin.

  • During normal conditions, one of their functions is to act as roadways for motor proteins.


  • Microtubules are also the central supports for cilia and flagella.

  • Covered by just the cell membrane, cilia and flagella extend from the cell.

  • Motor proteins push/pull on the tubules within the cilium/flagellum.

  • This causes them to move back and forth.

Cell membranes
Cell Membranes

  • Phospholipids are the dominant molecule in membranes.

  • Phospholipids naturally assemble into a bilayer

  • The membrane’s center is hydrophobic because of the fatty acid tails.

  • The outer edges are hydrophilic because of the phosphate groups.

Cell transport
Cell Transport

  • A membrane is a selectively permeable barrier

  • Single molecules that are nonpolar or only slightly polar can pass through the hydrophobic core without problems.

  • These include O2, N2, CO2, steroids, alcohols, fatty acids, and pesticides.

  • The cell cannot regulate movement of these molecules as they follow the rules of simple diffusion

Cell transport1
Cell Transport

  • Single molecules that are polar or charged require a transport protein or channel protein to pass through the core.

  • These include H20, ions, sugars, amino acids, and proteins.

  • Their movements

    into / out of the cell

    can be regulated by

    modifying the

    proteins involved.


  • Materials can move pass membranes:

    • A) as single molecules (diffusion and active transport) or in large quantities (vesicular transport)

    • B) without input of energy (passive transport) or requiring energy (active transport)

    • C) without the help of a protein (simple diffusion) or with the help of a protein (facilitated and channel-mediated diffusion).


  • During diffusion, molecules move from areas of higher concentration to areas of lower concentration, “down” the concentration gradient.

  • At equilibrium, movements of molecules in one direction are balanced by movements in the opposite direction.


  • Diffusion rates depend on:

    • a) the distance over which molecules must move:

      • shorter (thinner membrane) = faster

    • b) the size of the molecule:

      • smaller = faster

    • c) the surface available for diffusion:

      • wider = faster

    • d) the speed that molecules are moving = temperature:

      • higher = faster

    • e) the concentration gradient between two points

      • greater concentration difference = faster.


  • Diffusion rates also depend on how permeable the membrane is to a particular kind of molecule

  • The diffusion rates of one type of molecule are independent of the concentrations of any other types of molecules

  • In simple diffusion, molecules move

    past the membrane through the lipid



  • In channel mediated diffusion, molecules pass the membrane through a protein pore.


  • Osmosis is the movement of “free” water down its concentration gradient.

  • Some water molecules surround solutes as part of spheres of hydration.

  • If a membrane is not permeable to that solute, then these water molecules cannot pass either.

  • A solution with few dissolved molecules (low osmolarity) will have more free water molecules than a solution with more dissolved molecules (high osmolarity).


  • Imagine that we have a selectively permeable membrane separating a 40% sugar solution from a 10% sugar solution.

  • There are more “free” water molecules on the 10% sugar side than there are on the 40% sugar side.

  • Because there are more “free” water molecules in the 10% side, water will move by osmosis (diffusion of water) to the 40% side.


  • If the concentration of dissolved materials is equal in the surrounding solution as in the cell, then no net movement of water occurs.


  • If the concentration of dissolved materials is greater in the solution than in the cell, then water will leave the cell. The solution is hypertonic compared to the cell.

  • If the concentration of dissolved materials is lower in the solution than in the cell, then water will enter the cell. The solution is hypotonic compared to the cell.


  • Specific carrier proteins allow materials that are not hydrophobic to pass through a membrane.

  • In facilitated diffusion, the carrier protein allows molecules to move from high concentration to low concentration.

  • Osmosis, facilitated diffusion, and standard diffusion are all examples of passive transport.

    • movement of materials down a concentration gradient without expenditure of energy

Active tranpsort
Active tranpsort

  • Active transport is the movement of materials across a membrane against its concentration gradient.

  • Molecules are pumped from low concentration to higher concentration.

  • Active transport requires metabolic energy to do the pumping.

  • In exocytosis a membrane-bound sac (a vesicle) fuses with a membrane and dumps the fluid contents outside the membrane (usually outside the cell).

  • Endocytosis is the reverse of exocytosis.

    • A region of membrane forms a pocket around the external materials, pinches off a vesicle, and transports this material inside.

  • In phagocytosis, the materials being brought insides are solid particles.

  • In pinocytosis, the materials being brought inside are fluids.

Endocytosis and exocytosis
Endocytosis membrane and dumps the fluid contents outside the membrane (usually outside the cell). and exocytosis

  • White blood cells actively use endocytosis and exocytosis in their role as defenders of the body from invaders.

  • When they detect a microbe, they extend fingers of membrane and cytoplasm to surround it.

  • When the membrane fingers meet, they fuse.