Cellular Biology Notes

 

I. Syllabus answers

 

1.1.1 Discuss the theory that living organisms are composed of cells.

  • All living things are made of cells, and that cells arise from other cells.
  • It is important to note that all "rules" have exceptions. Skeletal muscles and some fungal hyphae are not divided into cells but have a multinucleate cytoplasm. Some biologists consider unicellular organisms to be acellular.

1.1.2 State that a virus is a non-cellular structure consisting of DNA or RNA surrounded by a protein coat.

  • A virus is a non-cellular structure consisting of DNA or RNA surrounded by a protein coat.

1.1.3 State that all cells are formed from other cells.

  • All cells are formed from other cells.

1.1.4 Explain three advantages of using light microscopes.

  • Advantages of using a light microscope include: color images instead of monochrome images (one color), easily prepared sample material, the possibility of observing living material and movement, and a larger field of view.

1.1.5 Outline the advantages of using electron microscopes.

  • Since the resolution is higher in an electron microscope than a light microscope, one can see more separate particles and have a clearer picture of those particles. Also, an electron microscope has a higher magnification than a light microscope, so one would be able to see smaller objects.

1.1.6 Define organelle.

  • An organelle is a discrete structure within a cell that has a specific function; it also needs to be covered by its own membrane.

1.1.7 Compare the relative sizes of molecules, cell membrane thickness, viruses, bacteria, organelles and cells, using appropriate SI units.

  • 1000 nm(nanometer) = 1 um, 1000 um = 1mm
  • Molecules are 1 nm while the thickness of a membrane is 10 nm. Viruses are 100 nm, bacteria are 1 um, organelles can be up to 10 um, and most cells can be up to 100 um. The cell is much larger than all these when taken into consideration the three-dimensional shape.

1.1.8 Calculate linear magnification of drawings.

 

1.1.9 Explain the importance of the surface area to volume ratio as a factor limiting cell size.

  • When a cell grows, the volume increases at a faster rate than the surface area. Thus, as the cell grows the surface to volume ratio decreases. A cell needs surface area in order to carry out metabolic functions (chemical reactions need a surface), and as a cell grows it needs to carry out more and more reactions. Therefore, since a cell must maintain a certain surface area to volume ratio, its size is limited.

1.1.10 State that unicellular organisms carry out all the functions of life.

  • Unicellular organisms carry out all the functions of life.

1.1.11 Explain that cells in multicellular organisms differentiate to carry out specialized functions by expressing some of their genes but not others.

  • In multicellular organisms, all the cells contain all the genes, but they do not use all of them. The cells of a multicellular organism differentiate to carry out specialized functions by only expressing some of their genes.

1.1.12 Define tissue, organ, and organ system.

  • A tissue is an integrated group of cells that have a common structure and function. An organ is a center of body function specialized for that one function that is composed of several different types of tissue. An organ system is a group of organs that specialize in a certain function together.

1.2.1 Draw a generalized prokaryotic cell as seen in electron micrographs.

 

1.2.2 State one function for each of the following: cell wall, plasma membrane, mesosome, cytoplasm, ribosomes and naked DNA.

  • One function of the cell wall is that it maintains the shape of the cell. The plasma membrane acts as a selective membrane that lets sufficient amounts of oxygen and other nutrients to enter and leave the cell as needed. A mesosome increases the cell's surface area for metabolic reactions to occur. The cytoplasm holds and suspends the organelles of specialized function. Ribosomes are the main site for protein synthesis and naked DNA contain genes which control the cell and contain its genotype.

1.2.3 State that prokaryotes show a wide range of metabolic activity including fermentation, photosynthesis and nitrogen fixation.

  • Prokaryotes show a wide range of metabolic activity including fermentation, photosynthesis and nitrogen fixation.

1.3.1 Draw a diagram to show the ultrastructure of a generalized animal cell as seen in electron micrographs.

 

1.3.2 State one function of each of these organelles: ribosomes, rough endoplasmic reticulum, lysosome, Golgi apparatus, mitochondion and nucleus.

  • The ribosomes are the main site for protein synthesis. The proteins made by ribosomes can be used inside the cell, or be sent out of the cell. One function of the rough endoplasmic reticulum is the portion of the endoplasmic reticulum that is studded with ribosomes. The proteins made in these ribosomes are packaged in the rough ER and are usually sent outside of the cell. A lysosome uses hydrolytic enzymes to digest macromolecules. The Golgi apparatus receives many of the products of the rough endoplasmic reticulum and it modifies them. Later these proteins are transported to other destinations in packages of membrane. A mitochondrion is the site of cellular respiration. The nucleus contains the DNA which controls and contains the genotype for the cell.

1.3.3 Compare prokaryotic and eukaryotic cells.

  • Both prokaryotic and eukaryotic cells have cell membranes and both carry out functions of cells (metabolic functions, reproduction etc).
  • In contrast to eukaryotes, prokaryotic cells have no organelles (no nucleus, no mitochondria, etc.). Prokaryotes have one circular loop of DNA that is located in the cytoplasm, whereas eukaryotic DNA is arranged in a very complex manner with many proteins and is located inside a nuclear envelope. Because the prokaryotic DNA is associated with very little protein, it is considered naked. Also, eukaryotic cells are much larger than prokaryotic cells. In addition, the ribosomes in prokaryotes and eukaryotes are structurally different. Prokaryotes have 70S ribosomes, whereas eukaryotes have 80S ribosomes.

1.3.4 Describe three differences between plant and animal cells.

  • Plant cells contain a cell wall while animal cells do not.
  • Plant cells have chloroplasts while animal cells do not. Animal cells contain mitochondria and plant cells do not.
  • Most animal cells do not contain large central vacuoles while most plant cells do.

1.3.5 State the composition and function of the plant cell wall.

  • The plant cell wall contains cellulose microfibrils which help to maintain the cell's shape.

1.4.1 Draw a diagram to show the fluid mosaic model of a biological membrane.

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1.4.2 Explain how the hydrophobic and hydrophilic properties of phospholipids help to maintain the structure of the cell membrane.

o        The head of the phospholipid is polar and hydrophilic (water-loving), and these heads make up the outside of the phospholipid bilayer. The tail of the phospholipid that is located inside the membrane is nonpolar and hydrophobic(water-fearing). Because one end of the phospholipid is hydrophobic and the other is hydrophilic, phospholipids naturally form bilayers in which the heads are facing outward (toward the water), and the tails are facing inward (away from the water). Therefore, the characteristics of phospholipids enable the phospholipids to form a stable structure.

1.4.3 List the functions of membrane proteins including hormone binding sites, enzymes, electron carriers, channels for passive transport and pumps for active transport.

o        Membrane proteins perform many tasks which help the cell with its functions. They act as hormone binding sites, enzymes, electron carriers, channels for passive transport and pumps for active transport.

1.4.4 Define diffusion and osmosis.

o        Diffusion is the total movement of particles from a region of higher concentration of that particle to a region of lower concentration of that particle. The difference in concentration that drives diffusion is called a concentration gradient. Osmosis is the passive movement of water molecules, across a partially permeable membrane, from a region of lower solute concentration to a region of higher solute concentration.

1.4.5 Explain passive transport across membranes in terms of diffusion.

o        Passive transport happens naturally (it requires no energy from the cell) if there is a concentration gradient between one side of the membrane and the other. This concentration gradient drives diffusion across the membrane.

1.4.6 Explain the role of protein pumps and ATP in active transport across membranes.

o        During active transport across membranes, the substance being transported goes against the gradient (it is going from where there is a lesser concentration to a greater concentration), and so energy is required to transport it in the form of ATP. Proton pumps in the cell membrane function in transporting particles across a membrane against concentration membranes with energy from ATP.

1.4.7 Explain how vesicles are used to transport materials within a cell between the rough endoplasmic reticulum, Golgi apparatus and plasma membrane.

o        Vesicles are membranous sacs in which materials are stored and transported throughout the cell. In order for the materials within a vesicle to go through a membrane (the membranes of organelles, or the cell's plasma membrane), the membranous vesicle becomes part of the organell's membrane or the plasma membrane, releasing the materials inside. The materials that were inside the vesicle are now free on the opposite side of the membrane.

1.4.8 Describe how the fluidity of the membrane allows it to change shape, break and reform during endocytosis and exocytosis.

o        Endocytosis is the movement of material into a cell by a process in which the plasma membrane engulfs extracellular material, forming membrane-bound sacs that enter the cytoplasm. Exocytosis is the movement of material out of a cell by a process in which intracellular material is enclosed within a vesicle that moves to the plasma membrae and fuses with it, releasing the material outside the cell.

o        The cell membrane is fluid in that it is constantly in motion. The movement of the phospholipids changes the membrane's shape, and allows for temporary holes in the membrane that let materials flow in and out of the cell. If the membrane were not fluid in nature, it would not be able to fuse with vesicles in endocytosis and exocytosis.

1.5.1 State that the cell-division cycle involves interphase, mitosis and cytokinesis.

  • The cell-division cycle involves interphase, mitosis and cytokinesis.

1.5.2 State that interphase is an active period in the life of a cell when many biochemical reactions occur, as well as DNA transcription and DNA replication.

  • Interphase is an active period in the life of a cell when many biochemical reactions occur, as well as DNA transcription and DNA replication.

1.5.3 Describe the events that occur in the four phases of mitosis (prophase, metaphase, anaphase and telophase).

  • Mitosis contains four phases which are prophase, metaphase, anaphase, and telophase. During mitosis, chromatin fibers become tightly coiled and can be seen as chromosomes. The chromosomes appear as two identical sister chromatids joined at the centromere. The mitotic spindle begins to from in the cytoplasm. Some of the microtubules that make up the spindle attach to the chromosomes. In metaphase the chromosomes line up on the cell equator, with each sister chromatid facing a different pole of the cell. During anaphase, the centromere replicates and the sister chromatids separate. These news chromosomes move to opposite poles, so that each pole of the cell contains a complete set of chromosomes. During telophase, the microtubules elongate the cell, further separating the two poles. Then the parent cell's nuclear envelope is broken down and fragments are used to form new nuclear envelopes.

1.5.4 Explain how mitosis produces two genetically identical nuclei.

  • During mitosis, pairs of two identical chromosomes are pulled to opposite ends of the cell. These identical chromosomes contain the same genetic information as the chromosomes of the parent cell, so they are genetically identical. The two identical sets of chromosomes become the nuclei of the two daughter cells.

1.5.5 Outline the differences in mitosis and cytokinesis between animal and plant cells.

  • The differences in plant and animal cell mitosis exist because the plant cell has a cell wall. Mitosis in plant cells involves the formation of a cell plate that separates the two daughter cells, while animal cells use a cleavage furrow to separate the two new cells. Also, plant cells lack the centrioles involved in animal cell mitosis.

1.5.6 State that growth, tissue repair and asexual reproduction involve mitosis.

  • Growth, tissue repair and asexual reproduction involve mitosis.

1.5.7 State that tumors (cancers) are the result of uncontrolled cell division and that these can occur in any organ.

  • Tumors (cancers) are the result of uncontrolled cell division and these can occur in any organ.

II. Class Notes

 

§         In eukaryotic cells, Histone Proteins attract to each other to form a ball of DNA called a chromosome.  Prokaryotic Cells lack Histones.  See picture.

§         The Mesosome increases cellular surface area for more metabolic reactions.  See picture.

§         Sizes:

Structure/Cell

Specific Example

1 Dimensional Size

Surface Area

Volume

Molecule

Triglyceride

1 nm

6 x 10-6 µm2

1 x 10-9 µm3

Membrane Thickness

Plasma Membrane

10 nm

6 x 10-4 µm2

1 x 10-6 µm3

Virus

Influenza

100 nm

6 x 10-2 µm2

1 x 10-3 µm3

Bacterium

Cholera

1 µm

6 µm2

1 µm3

Organelle

Mitochondrion

10 µm

600 µm2

1000 µm3

Eukaryotic Cell

Neuron

100 µm

600000 µm2

1000000 µm3

 

§         Protein Synthesis and Secretion

 

§         Membrane Proteins

    • Hormone Binding Sites – Insulin binding site
    • Membrane-Bound Enzymes

Ø      Villi enzymes: Aminopeptidases attack amino terminal of peptides with amino acids in order to digest.  (Act as digestive catalyst).

o       Electron Carriers

Ø      Part of photosynthesis.  Electron carriers in the electron transport system pass electrons from one to another in producing ATP (Phosphospherylation).

o       Transport Channels

Ø      Selectively permeable and only allow certain molecules to enter.  Ions can’t move between cytoplasm and intercellular fluid without transport proteins (dialysis).

o       Membrane Pumps

Ø      Sodium Potassium pump actively pumps Na out of the cell and K into the cell, creating an electrical gradient across the cell membrane.  Outside becomes positively charged and the inside becomes negatively charged.  Important for electrical conductivity along neurons.

§         Transport Mechanisms

o       Active (uses ATP across concentration gradient)

Ø      Protein pump (ex. NaK pump)

Ø      Endocytosis

v     Phenocytosis: small molecules

v     Phagocytosis: large molecules

v     Pinocytosis: liquids

Ø      Exocytosis/Secretion

o       Passive (diffusion)

Ø      Dialysis: Small molecules (not H2O) anywhere through membrane [ex. ions]

Ø      Facilitated Diffusion: Medium-sized molecules (not H2O) through channels [ex. glucose]

Ø      Osmosis: H2O through semi permeable membrane following its own concentration gradient

v     Water Potential = Water movement + Built up pressure

v     Turgor pressure – Water pressure within cell

v     In animal cells, which lack cell walls, cytolysis can occur with too much pressure:

§         Endosymbiosis – a theory stating that at one time Chloroplasts and Mitochondria were prokaryotic cells

§         Fluid Mosaic Theory – theory stating that plasma membranes’ phospholipid bilayers allow movement (fluid) while being comprised of proteins and other molecules (mosaic).

 

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