BIOL #05

Question 1

Grouping Cells

Answer 1

According to morphology, there are two broad groupings of life:

1. Prokaryotes, lack a membrane-bound nucleus
2. Eukaryotes, have a membrane-bound nucleus

According to phylogeny, or evolutionary history, there are three domains:

1. Bacteria - prokaryotic
2. Archaea - prokaryotic
3. Eukarya – eukaryotic

Question 1

Prokaryotic Cells: Genetic Information

Answer 1

• Most prokaryotic species have one supercoiled circular chromosome found in the nucleoid region of the cell.
– The chromosome contains a long strand of DNA and a few supportive proteins.

• In addition to the large chromosome, many bacteria contain plasmids.
– Small, supercoiled, circular DNA molecules
– Plasmids usually contain genes for adapting to unusual environmental conditions.

Question 2

Prokaryotic Cells: Internal Structure

Answer 2

• In addition to the nucleoid chromosome and plasmids, other structures are contained within the cytoplasm:
– All prokaryotic cells contain ribosomes, consisting of RNA molecules and protein, for protein synthesis.
– The inside of many prokaryotic cells is supported by a cytoskeleton of long, thin protein filaments.

Question 3

Prokaryotic Cells: External Structure

Answer 3

• Some prokaryotes have tail-like flagella on the cell surface that spin around to move the cell.
– Bacterial and eukaryotic flagella do not share many structural characteristics, and likely arose independently.

• Most prokaryotes also have a cell wall.
– Bacterial and archaeal cell walls are a tough, fibrous layer that surrounds the plasma membrane
– Maintains shape and protect the cell

• The cell wall of bacteria is made of the polysaccaride peptidoglycan
• Archaea cell walls contain polysaccarides and proteins but lack peptidoglycan

Question 4

Gram staining

Answer 4

used to classify bacteria into groups based on differences in their cell walls
• Gram-positive bacteria: simplier walls
with large amounts of peptidoglycan
• Gram-negative bacteria: more complex
walls, less peptidoglycan, plus an extra
outer membrane

Question 5

Glycolipids or Lipopolysaccharides

Answer 5

• The extra outermembrane in gram-negative bacteria is composed of glycolipids or lipopolysaccharides
• Glycolipids are carbohydrates bonded to lipids
• These structures cause toxic reactions (fever, shock) in humans and provide protection from many types of antibiotics.

Question 6

Bacteria Capsule

Answer 6

• Some bacteria have a sticky layer of polysaccharide or protein surrounding the cell wall called a bacteria capsule
• Used for aggregation or protection

Question 7

Fimbriae

Answer 7

• Some bacteria attach to each other or substrates with fimbriae (hair-like appendages)

Question 8

What limits cell size?

Answer 8

• Limitations to cell size apply to both prokaryotes and eukaryotes
• Even larger eukaryotic cells cannot surpass a certain size threshold (with few exceptions)

• Metabolic requirements of the cell impose a limit on size because only a limited amount of any substance can cross a cell’s membrane in a fixed amount of time
– Cell’s must shuttle oxygen, nutrients, and wastes in and out of the cell in order to perform
vital cellular functions

• The ratio of the surface area to volume is critical to cell functioning

Question 9

The Nucleus

Answer 9

• STRUCTURE:
– Large and highly organized
– The nucleus is surrounded by a double-membrane nuclear envelope.
– The nucleus has a distinct region called the nucleolus.

• FUNCTION:
– Information storage and processing
• Contains the cell’s chromosomes ( structures carrying genetic information)
• Directs protein synthesis (makes messenger RNA)
– Ribosomal RNA synthesis (in the nucleolus)

Question 10

The Endomembrane System

Answer 10

The endomembrane system is composed of the smooth and rough ER, the Golgi apparatus, lysosomes, the nuclear envelope, and the plasma membrane and is the primary system for protein and lipid synthesis and transport.

Ions, ATP, amino acids, and other small molecules diffuse randomly throughout the cell, but the movement of proteins and other large molecules is energy demanding and tightly regulated.

Question 11

Rough Endoplasmic Reticulum

Answer 11

• STRUCTURE:
– The rough endoplasmic reticulum (rough ER, RER) is a network of membrane-bound tubes and sacs studded with ribosomes.
• The interior is called the lumen.
– The rough ER is continuous with the nuclear envelope.

• FUNCTION:
– Ribosomes associated with the rough ER synthesize proteins.
– New proteins (particularly proteins to be secreted by the cell) are folded and processed in the rough ER lumen.
– Builds more membrane

Question 12

Ribosomes

Answer 12

• STRUCTURE:
– Ribosomes are non-membranous (they are not
considered organelles).
– Have large and small subunits, both containing RNA
molecules and protein (subunits made in nucleolus)
– Ribosomes can be attached to the rough ER or free in the cytosol, the fluid part of the cytoplasm.

• FUNCTION:
– Protein synthesis

Question 13

Smooth Endoplasmic Reticulum

Answer 13

• STRUCTURE:
– The smooth endoplasmic reticulum is a network of membranebound tubes and sacs.
• The interior is called the lumen.
• No ribosomes are attached to its exterior

• FUNCTION:
– Synthesize lipids and steroids, drug/toxin detoxification, and several other functions.
– Serves different functions in different types of cells
• Hormone production in testes and ovarian cells
• Detoxification in liver cells

Question 14

Golgi Apparatus

Answer 14

• STRUCTURE:
– The Golgi apparatus is formed by a series of stacked flat membranous sacs called cisternae.

• FUNCTION:
– The Golgi apparatus processes, sorts, and ships
proteins synthesized in the rough ER.
– Membranous vesicles carry materials to and from the organelle.

Question 15

Lysosomes

Answer 15

• STRUCTURE:
– Lysosomes are single-membrane-bound structures containing approximately 40 different digestive enzymes.
– Lysosomes are only found in animal cells.

• FUNCTION:
– Lysosomes are used for digestion and waste processing
• Hydrolyze macromolecules
• Contain an acidic environment ptimal for the enzymes present inside

Question 16

How Are Materials Delivered to Lysosomes?

Answer 16

• Materials are delivered to the lysosomes by three processes:
– Autophagy: break down own cell material
– Phagocytosis: endocytosis of solid material
– Receptor-mediated endocytosis

• Endocytosis is a process by which the cell membrane can pinch off a vesicle to bring outside material into the cell.
– These vesicles merge with lysosomes to digest the material
– In addition to phagocytosis and receptor-mediated endocytosis, a third type of endocytosis called pinocytosis brings fluid into the cell.

Question 17

Vacuoles

Answer 17

• STRUCTURE:
– Vacuoles are large vesicles derived from the ER and golgi apparatus

• FUNCTION:
– Selectively transports solutes
– Performs different function in different cells
• Transportation of food in animal cells
• Large central reservoir for ion and water storage in plants
• In plant cells, vacuoles can perform functions similar to the lysosomes of animal cells (hydrolytic vacuoles)

Question 18

Peroxisomes

Answer 18

• STRUCTURE:
– Peroxisomes are globular organelles bound by a single membrane.

• FUNCTION:
– Center of oxidation reactions (especially breaking down long fatty acid chains so the fatty acids can be sent to the mitochondria to produce energy )
– Breaks down hydrogen peroxide – H2O2 – a harmful by-product of fatty acid break-down
• Uses the enzyme catalase

• Specialized peroxisomes in plant seeds called glyoxysomes are packed with enzymes that oxidize fats to form a compound that can be used to store energy for the cells in the seeds.

Question 19

Mitochondria: Powerhouse

Answer 19

• STRUCTURE:
– Mitochondria have two membranes; the inner one is folded into a series of sac-like cristae. The solution inside the cristae is called the mitochondrial matrix.
– Mitochondria have their own DNA and manufacture their own ribosomes.

• FUNCTION:
– ATP production is a mitochondrion’s core function (via cellular respiration)
– Some of the enzymes in the mitochondrial matrix catalyze steps of cellular respiration, others that function in ATP production are built into the inner membrane

Question 20

Chloroplasts

Answer 20

• STRUCTURE:
– Chloroplasts are lens-shaped organelles found in leaves and other green organs of plants and algae
– Consists of a two-membrane envelope with another membranous system of flattened interconnected sacs (thylakoids) inside
– A fluid called the stroma surrounds the thylakoids and contains chloroplast DNA, ribosomes, and many enzymes

• FUNCTION:
– Contain the green pigment, chlorophyll, along with enzymes and other molecules that function in the photosynthetic production of sugar

Question 21

Cytoskeleton

Answer 21

• The cytoskeleton
– composed of protein fibers
– gives the cell shape and structural stability
– aids cell movement and transport of materials within the cell.

• Cytoskeleton organizes all of the organelles and other cellular structures into a cohesive whole.

Question 22

The Dynamic Cytoskeleton

Answer 22

• The cytoskeleton is a complex network of fibers that helps maintain cell shape by providing structural support
• The cytoskeleton is dynamic – it changes to alter the cell’s shape, to transport materials in the cell, or to move the cell itself.

• There are three types of cytoskeletal elements:
– Actin filaments (microfilaments)
– Intermediate filaments
– Microtubules

Question 23

Actin Filaments (microfilaments)

Answer 23

• Actin filaments are the smallest cytoskeletal elements.

• Actin filaments form by polymerization of
individual actin protein molecules.

• Actin filaments are grouped together into long bundles or dense networks that are usually found just inside the plasma membrane and help define the cell’s shape.

Question 24

Actin-Myosin Interactions

Answer 24

• Actin filaments can also be involved in
movement by interacting with the motor protein myosin.

• Actin-myosin interactions can cause
cell movements such as cell crawling, cytokinesis, and cytoplasmic streaming.

Question 25

Intermediate Filaments

Answer 25

• Intermediate filaments are defined by size rather than composition. Many types of intermediate filaments exist, each consisting of a different protein.
• Intermediate filaments provide structural support for the cell. They are not involved in movement.

• Intermediate filaments form a flexible skeleton that helps shape the cell surface and hold the nucleus in place.
– These are more permanent structures than microfilaments and microtubules, which can be disassembled and reassembled around the cell

Question 26

Microtubule Structure & Function

Answer 26

• Microtubules are large, hollow tubes made of the protein tubulin and formed into dimers (compounds with two-subunits)
• Microtubules have polarity, are dynamic, and usually grow at their positive ends.
• Microtubules provide a stable, structural framework for the cell as well as individual organelles.

• Also involved in movement
– Microtubules can act as “railroad tracks” to carry vesicles
– Involved in chromosome separation during cell division

Question 27

Microtubule Organizing Center

Answer 27

• Microtubules originate from the microtubule organizing center and grow
outward, radiating throughout the cell.

• Animal cells have a microtubule organizing center called the centrosome
– Centrosomes contain two bundles of microtubules called centrioles

• Although the cells of other eukaryotes have well-organized microtubules, almost all lack centrosomes with centrioles

Question 28

Microtubule Function

Answer 28

• Transport vesicles move through the cell along microtubule tracks in an energy-dependent process (require ATP and kinesin)
– Kinesin is a motor protein that converts chemical energy in ATP into mechanical work

Question 29

Cilia and Flagella

Answer 29

• Flagella are long, hair-like projections from the cell surface that move cells.
– Bacterial flagella are made of flagellin and rotate like a propeller.
– Eukaryotic flagella are made of microtubules and wave back and forth.

• Closely related to eukaryotic flagella are cilia, which are short, filament-like projections.
• Cells generally have just one or two flagella but may have many cilia.

Question 30

Cilia and Flagella Structure

Answer 30

• The structure of cilia and flagella are due to a specialized arrangement of microtubules, called the axoneme
• The axoneme is a complex “9 + 2” arrangement of microtubules connected by links and spokes.
• The axoneme of cilia and flagella attaches to the cell at a structure called the basal body.

Question 31

Dynein

Answer 31

• The motor protein dynein forms the arms between doublets and changes shape when ATP is hydrolyzed – dynein “walks” up the microtubule.
• When the dynein arms on just one side of the axoneme move, cilia and flagella bend instead of elongating because the links and bridges constrain movement of the microtubule doublets.