Prokaryotes Vs. Eukaryotes (1.2)

Question 1

Cells are either…? Include examples

Answer 1

Prokaryotic or Eukaryotic.

Bacteria and archaea are prokaryotes. All other life, including plants, animals, fungi, and protists, are eukaryotes.

Question 2

Outline the major differences between prokaryotic and eukaryotic cells.

Answer 2

Prokaryotic Cells
- Smaller (about 0.2 - 2 um)
- DNA in the nucleoid region (no nuclear membrane)
- No membrane bound organelles
- Cell wall (of peptidoglycan)
- Smaller ribosomes (70s) in the cytoplasm
- DNA is circular and without histone proteins
- Has plasmid DNA
- Asexual cell division-binary fission

Eukaryotic Cells
- Bigger (10-100 um)
- DNA in a true nucleus
- Membrane-bound organelles present
- Cell wall of cellulose (plants) or chitin (fungus)
- Larger ribosomes (80s) in the cytoplasm and on ER
- //also has 70s ribosomes within mitochondria and chloroplasts//
- DNA is linear with histone proteins
- Do not have plasmid DNA
- Asexual or sexual cell division

Question 3

List the functions of the cell membrane.

Answer 3

• Forms the boundary of the cell
• Acts as a selective barrier, allowing certain materials to pass into and out of the cell but not others (composition regulator).

Question 4

List the functions of the nucleoid.

Answer 4

• Location of the genetic material for inheritance and protein coding;
• Circular DNA
• Not associated with histone proteins
  DNA with ends that come together to form a circle and is NOT wrapped around proteins (termed “naked”)

Question 5

List the functions of the plasmid.

Answer 5

• Smaller, circular DNA is not associated with DNA in the nucleoid.
• Often contains genes for antibiotic resistance
• Extra piece(s) of small, circular DNA that can be shared between bacteria,

Question 6

List the functions of the cytoplasm.

Answer 6

• Gel-like fluid made up of primarily water and dissolved molecules
• Stage/site of many metabolic reactions

Question 7

List the functions of the Pilus (singular).

Answer 7

• Found in some (not all) prokaryotic cells
• Hair-like structures
• Help the cell attach to surfaces
• Enable the cell to swap DNA with other cells, and may be used to harpoon DNA in the environment

Question 8

List the functions of the Flagella.

Answer 8

• Found in some (not all) prokaryotic cells
• Long extension used for cell locomotion

Question 9

List the functions of the Cell Wall

Answer 9

• Provides shape and allows the cell to withstand turgor pressure without bursting

Question 10

List the functions of the Capsule.

Answer 10

• Found in some (not all) prokaryotic cells
• Helps the cell maintain moisture and adhere to surfaces.
• Protects the cells from other organisms

Question 11

What are the external organelles of a prokaryotic cell?

Answer 11

• Cell wall
• Pili
• Capsule
• Flagellum

Question 12

What organelles strengthen the Endosymbiotic Theory and how?

Answer 12

Both mitochondria and chloroplasts also have 70s ribosomes. This serves as genetic evidence for the Endosymbiotic Theory which states that chloroplasts and mitochondria evolved from small symbiotic prokaryotes that lived within other, larger host cells.

Both mitochondria and chloroplasts also reproduce independently of the host cell through a process similar to binary fission. This serves as genetic evidence for the Endosymbiotic Theory which states that chloroplasts and mitochondria evolved from small symbiotic prokaryotes that lived within other, larger host cells

Question 13

State the meaning and advantages of eukaryotic cells being “compartmentalized.”

Answer 13

• Compartmentalization is the presence of membrane-bound partitions (organelles) within the eukaryotic cell. The compartments allow for:
• Specialization of regions within the cell for specific functions.
• Molecules are needed for a specific function to be concentrated in a region within the cell.
• An organelle creates a compartment with controlled conditions inside. These micro-environments are often distinct from the environment of the surrounding cytosol and are tailored to the specific functions of the organelle
• Higher efficiency, allowing each part of the cell to
  flourish in its tiny environment.

Question 14

What are some examples of compartmentalized structures and how do they become more efficient?

Answer 14

• Lysosomes: maintain an environment that is more acidic than the surrounding cytosol, because its enzymes require a lower pH to catalyze reactions. Similarly, pH is regulated within mitochondria, which helps them carry out their function of producing energy.
• Some proteins require an oxidative environment for proper folding and processing, but the cytosol is generally reductive. Therefore, these proteins are produced by ribosomes in the endoplasmic reticulum (ER), which maintains the necessary environment. Proteins are often then transported within the cell through membrane-bound vesicles.
• The genetic material of eukaryotic cells is compartmentalized within the nucleus, which is surrounded by a double membrane called the nuclear envelope. The nucleus represents an additional protective enclosure of the DNA. As a result, eukaryotic DNA is less susceptible to mutations.

Question 15

State structural differences between plant and animal cells.

Answer 15

Animal Cells
- No cell wall
- No chloroplasts
- No large vacuole
- Not a fixed shape
- Stores carbohydrates as glycogen

Plant Cells
- Cell wall
- Chloroplasts
- Large vacuole
- Fixed shape
- Stores carbohydrates as starch

Question 16

Define asexual reproduction

Answer 16

• Asexual reproduction creates offspring from a single-parent organism.
• The offspring are genetic clones of that parent.
• Binary fission and mitosis are mechanisms of asexual reproduction.

Question 17

Outline the four steps of binary fission.

Answer 17

1. The cell must prepare first, it must have enough resources and energy to divide.
2. The nucleoid DNA replicates to create an exact duplicate copy.
3. The nucleoid DNAs attach to the cell membrane. The cell membrane (and wall, if present) grow, causing the cell to elongate and the DNA molecules to move apart from each other.
   - 4. The cell membrane pinches inward, creating furrows at the end of the cell until they combine (called the septum) and make genetically identical cells.

Finally, Daughter Cells: The two daughter cells that result from binary fission are genetically identical to the single cell from which they arose.

Question 18

Define resolution

Answer 18

The smallest interval distinguishable by the microscope, which then corresponds to the degree of detail visible in an image created by the instrument.

Question 19

Compare the functionality of light and electron microscopes.

Answer 19

• LIGHT MICROSCOPES*
  
  • Use lenses to bend light and magnify images.
  • Used to study dead or living cells in color.
  • Cell movement can be studied.
  • Larger field of view.
  • Objects can be magnified up to 2000X.
  • Can resolve objects 200 nm apart.
• ELECTRON MICROSCOPES*
  
  • Uses electron beams focused by electromagnets to magnify and resolve.
  • Requires cells to be killed and chemically treated before viewing.
  • No movement can be seen.
  • Without stain or dye, no color can be seen.
  • Smaller field of view.
  • Can magnify objects up to 250,000 times.
  • Can resolve objects that are 0.2 nm apart.

Question 20

State the function of an exocrine gland cell.

Answer 20

• Exocrine gland cells synthesize molecules (often proteins) for secretion from the cell into an external space by a way of duct.
• Exocrine gland cells of the pancreas secrete enzymes that function in digestion in the small intestine.

Question 21

Why is the exocrine cells different from others?

Answer 21

The exocrine gland cells of the pancreas secrete digestive enzymes, which travel into the small intestine and help break down nutrients from food. In order to carry out this job, the cells have to get those enzymes shipped from their site of synthesis—inside the cell—to their place of action—outside the cell. It should come as no surprise that the exocrine gland cells will have differentiated into cells with specific compartmentalized structures, unique shapes, and specific chemistry that collectively allow the cell to perform its function with the highest efficiency possible.

Question 22

Describe the function of the following structures in an exocrine gland cell: plasma membrane, nucleus, mitochondria, Golgi apparatus, lysosomes, vesicles and endoplasmic reticulum.

Answer 22

• Plasma membrane: Forms the boundary of the cell and acts as a selective barrier allowing certain materials to pass into and out of the cell. The fluidity of the membrane allows for the secretion of substances via exocytosis from the exocrine gland cell
• Nucleus: contains most of the genes that control the eukaryotic cell, contains the nucleolus and chromatin.
• Mitochondria: The location of aerobic cellular respiration used to make ATP. The ATP is then used to fuel the
  exocrine gland cell’s protein synthesis, active transport, and exocytosis
• Golgi apparatus: Consists of flattened membranous sacs; receives transport vesicles from the ER, modifies proteins produced in the ER, produces secretory vesicles. Depending on the contents the vesicle is despatched to one of three destinations:
  - Within the cell, to organelles called lysosomes.
  - The plasma membrane of the cell.
  - Secretion to the outside of the cell.
• Lysosome: Contains digestive enzymes that are used to break apart cellular debris and waste (The enzymes digest large nutrient molecules, and/or degrade and recycle the components of the cell’s organelles when they are old or damaged, or if the cell is ‘starving’ in the absence of nutrients).
• Vesicles: Transport materials within the cell and out of the cell via exocytosis. Secretory vesicles are also how new phospholipids are added to the cell membrane, during exocytosis

Peroxisome: Store enzymes that require oxygen (oxidative enzymes). Contain enzymes that break down fatty acids, amino acids, and alcohol, resulting in the production of the toxic substance, hydrogen peroxide. Also contain high levels of the enzyme catalase which breaks down the hydrogen peroxide into harmless products, O2 and H2O.

Rough Endoplasmic Reticulum: Series of connected flattened membranous sacs that play a central role in the synthesis and transport of proteins. Has bound ribosomes, which are protein-synthesizing structures. The RER membrane is continuous with the nuclear envelope, which surrounds the cell nucleus; is involved with the production, folding, quality control, and despatch of some proteins

Smooth Endoplasmic Reticulum: In contrast to the RER, the smooth endoplasmic reticulum lacks ribosomes and is not involved in protein synthesis. The main functions of SER are the synthesis of phospholipids and cholesterol and the synthesis and repair of membranes. Series of connected flattened membranous sacs that are continuous with the RER.

Question 23

State the function of a palisade mesophyll cell.

Answer 23

Palisade mesophyll cells are found on the upper surface of a leaf and have the primary job of performing photosynthesis. They are rectangular cells just under the upper surface of the leaf. These cells contain the largest number of chloroplasts per cell, which makes them the primary site of photosynthesis, converting the energy in light to the chemical energy of carbohydrates. Beneath the palisade mesophyll are the spongy mesophyll cells, which also perform photosynthesis and have many intercellular spaces that allow the passage of gases into and out of the leaf stoma

Question 24

Why are the palisade mesophyll cells differentiated?

Answer 24

The palisade mesophyll cells of the leaf perform photosynthesis. It should come as no surprise that the palisade mesophyll cells have differentiated into cells with specific compartmentalized structures, a unique shape, and specific chemistry that collectively allow the cell to perform its function with the highest efficiency possible.

Question 25

Describe the function of the following structures in a palisade mesophyll cell: cell wall, plasma membrane, chloroplasts, vacuole, nucleus, and mitochondria.

Answer 25

• Cell wall: The cell wall is a rigid layer that is found outside the cell membrane and surrounds the cell. The cell wall is primarily made of the structural polysaccharide cellulose. The cell wall provides structural support and protection. The cell wall prevents the plant cell from bursting when water enters the cell.
• Plasma membrane: Forms the boundary of the cell and acts as a selective barrier allowing certain materials to pass into and out of the cell. The cell membrane is flexible, allowing the plant cell to expand and contract under different environmental conditions as it loses and gains water.
• Chloroplasts: Location of photosynthesis, which captures light energy and uses it with water and carbon dioxide to produce glucose. Within the chloroplasts are light-absorbing pigments such as chlorophyll, which give the chloroplast its characteristic green color. The structure of the chloroplast is related to its function in photosynthesis.
• Vacuole: Mature plant cells have a central vacuole that occupies 30% - 90% of the volume of the cell.
  In addition to water storage, the main role of the vacuole is to maintain turgor pressure against the cell wall. The turgor pressure is the mechanism the plants use to remain upright.
• Nucleus: Contains most of the genes that control the eukaryotic cell, contains the nucleolus and chromatin.
• Mitochondria: The location of aerobic cellular respiration used to make ATP.

Question 26

Explain why cells with different functions will have different structures.

Answer 26

• Cells will have different types and/or quantities of organelles depending on the primary function of the cell type.
• This allows for cells to specialize for a specific task.