Eukaryotes

Question 1

Eukaryotes

Answer 1

• Eukarya
• Much more complex than prokaryotic cells

Question 2

Endosymbiont Theory

Answer 2

• States that the creation of eukaryotes was a singular and highly unlikely event
• Eukaryotic cells were created when an ancestral archaea cell engulfed an ancestral bacterial cell
• Instead of consuming the bacteria, the two cells fused
• This fusion resulted in Eukaryotic cells
• Double the number of organelles and DNA necessary for life
• Redundant organelles and DNA: two copies in the cell, only one is required for life
• The cell can undergo mutations in the second set of organelles/DNA and keep on functioning with the first set of organelles

Question 3

Evidence of Endosymbiont Theory

Answer 3

• Both mitochondria and chloroplasts have some of their own DNA, not DNA from the cell’s nucleus
• Both mitochondria and chloroplasts have double layered membranes, as if one membrane (eukaryotic) engulfed a second membrane (bacteria)
• Both mitochondria and chloroplasts still superficially resemble some free-living bacteria

Question 4

Cytosol

Answer 4

• The cytosol or cytoplasmic matrix is the liquid found inside cells

Question 5

Cytoplasm

Answer 5

• The area within the plasma membrane, which comprises of the cytosol, the mitochondria, plastids, and other organelles, but not the nucleus

Question 6

Endomembrane System

Answer 6

• Composed of the nucleus, nuclear membrane, nucleolus, nuclear pore, ribosome, rough endoplasmic reticulum, smooth endoplasmic reticulum, golgi apparatus, vesicle, lysosome, plasmid, vacuole
• Eukaryotic cells are highly structured and divided into multiple internal compartments by internal membranes: these internal compartments are not isolated from each other, they communicate
• This system of communication utilizing membranes is called the endomembrane system

Question 7

Nucleus

Answer 7

• Stores the DNA

Question 8

Nuclear Envelope

Answer 8

• Defines the boundary of the nucleus
• Consists of two membranes (inner and outer) each is a separate lipid bilayer
• Also contains the nuclear pores

Question 9

Nucleous

Answer 9

• Appears as a mass of densely stained granules and fibers
• Site where rRNA is synthesized
• Assembly site of large and small ribosomal subunits

Question 10

Nuclear Pores

Answer 10

• Act as gateways allowing molecules to enter and leave the nucleus

Question 11

Ribosomes

Answer 11

• Complexes made of rRNA and proteins
• Sites of proteins synthesis, in which amino acids are assembled into polypeptides
• Ribosomes can be free in the cytosol or bound with the endoplasmic reticulum membrane

Question 12

Endoplasmic Reticulum

Answer 12

• Continuous with the nuclear envelope
• Accounts for more than half of the total membrane in many eukaryotic cells
• Network of membranous tubules and cisternae
• Two distinct regions of the endoplasmic reticulum that differ in structure and function: rough and smooth

Question 13

Rough Endoplasmic Reticulum

Answer 13

• Studded with ribosomes on the surface of the membrane
• Synthesis of proteins that are to be secreted
• Synthesis of membranes

Question 14

Smooth Endoplasmic Reticulum

Answer 14

• Outer surface lacks ribosomes
• Functions in diverse metabolic processes, which vary with cell type
• Synthesis of: lipids, metabolism of carbohydrates, detoxification of drugs and poisons, storage of calcium ions

Question 15

Golgi Apparatus

Answer 15

• Looks like a series of flattened membrane sacs, called cisternae
• Stacked cisternae are surrounded by many small vesicles
• Not physically continuous with the endoplasmic reticulum
• Next stop for most vesicles budding from the endoplasmic reticulum
• Three primary roles: Further modifies the lipids and proteins produced by the endoplasmic reticulum, acts as a sorting station, synthesis of carbohydrates

Question 16

Vesicles

Answer 16

• Structure composed of a lipid bilayer
• Used to move items within the cell (or take items from the environment which cannot pass through the plasma membrane)
• Can be derived from other organelles containing membranes
• Can contain messenger signals for communication between organelles

Question 17

Lysosome

Answer 17

• Specialized vesicles derived from the golgi apparatus
• Responsible for intracellular digestion (phagocytosis and autophagy)
• Membrane-bound proton pumps keep the internal environment at an acidic pH of around 5 (optimal pH for degrading enzymes)

Question 18

Phagocytosis

Answer 18

• Amoebas (and other protists) and certain white blood cells are able to extend their plasma membranes and engulf smaller organisms (such as bacteria or damaged cells)
• Engulfed material fuses with a lysosome, using the acidic pH of the lysosome to digest the material

Question 19

Autophagy

Answer 19

• Lysosomes also use their hydrolytic enzymes to recycle the cell’s own organic material, a process called autophagy
• “Self-eating”
• Cleaning up the cell!

Question 20

Vacuoles

Answer 20

• Large vesicles derived from the endoplasmic reticulum and golgi apparatus
• Perform a variety of functions (food vacuole, contractile vacuole, central vacuole)

Question 21

Mitochondria

Answer 21

• Found in all eukaryotic cells
• Sites of cellular respiration
• Some cells have a single large mitochondrion
• More often a cell has hundreds to thousands of mitochondria
• Greater activity in cell = more mitochondria!
• Enclosed by two membranes; outer membrane is smooth, inner membrane is convoluted, with infoldings called cristae
• Inner membrane divides mitochondrion into: inner membrane space (narrow region between inner and outer membrane) and mitochondrial matrix (contains enzymes, mitochondrial DNA, and ribosomes)

Question 22

Chloroplast

Answer 22

• Chloroplasts capture the energy of sunlight to synthesize sugars; a process known as photosynthesis
• Surrounded by a double membrane and also have internal membrane-bound compartments called thylakoid
• Chloroplasts are found in most plants and some protists
• Some plants have lost chloroplasts through evolution (these species live as parasites draining sugars from their hosts… without chloroplasts, they can’t make sugars of their own!)

Question 23

Thylakoid

Answer 23

• Internal membrane-bound compartments inside chloroplasts
• Thylakoid membrane contains specialized light-collecting molecules (such as chlorophyll II)

Question 24

Cytoskeleton

Answer 24

• Complex internal structures of eukaryotic cell (not just floating freely inside the cell)
• Network of proteins and fibers supporting organelles and facilitating movement within the cell
• This network is a kind of internal ‘skeleton’ for the cell, referred to as the cytoskeleton
• Composed of microtubules, microfilaments, and intermediate filaments

Question 25

Microtubules

Answer 25

• Found in all eukaryotes
• Hollow rods constructed from protein dimer called tubulin
• α-tubulin and β-tubulin
• Shape and support the cell (compression resistant)
• Serve as tracks along which organelles with motor proteins can move
• Form cilia and flagella in eukaryotes
• Involved in separating the chromosomes during mitosis

Question 26

Centrosome

Answer 26

• Region located near the nucleus of animal cells considered to be a “microtubule-organizing center”
• Are composed of 2 centrioles
• Function as compression resistant girders
• Are responsible for moving organelles and pulling the cell apart during division

Question 27

Microfilaments

Answer 27

• Found in all eukaryotes
• Solid rods
• Also called actin filaments as they are built from molecules of actin
• Can form structural networks
• Tension bearing
• 3D networks support cell shape
• Involved in cell motility
• Serve as tracks along which organelles with motor proteins can move

Question 28

Myosin

Answer 28

• A motor protein (moves things) associated with microfilaments
• It uses microfilaments as tracks to move vesicles throughout the cell
• In a muscle cell, pulls microfilaments closer together (contraction)
• The energy required comes from the energy stored in ATP

Question 29

Intermediate Filaments

Answer 29

• Found ONLY in animal cells
• Not as frequently disassembled or reassembled as microtubules or microfilaments
• Especially sturdy (remain intact in cells after cell death)
• Tension-bearing
• Reinforce the cell’s shape and fixes the position of certain organelles

Question 30

Cell Adhesion

Answer 30

• Occurs in extracellular space
• Tight function: prevent leakages of extracellular fluid across a layer of epithelial cells by forming continuous seals around the cell
• Desmosome: function like rivets, fastening cells together in strong sheets (intermediate filaments anchor desmosomes together), attach muscle cells to each other
• Gap junction: provide cytoplasmic channels from one cell to an adjacent cell, channels can open and close

Question 31

Extracellular Matrix

Answer 31

• Occurs in extracellular space
• Found in most tissues (abundant in connective tissue)
• Mainly composed of glycoproteins and other carbohydrate-containing “fibrous” molecules (elastin, collagen)
• Many roles, including…
• Helps cells remain attached
• Cell-to-cell communication
• Cell movement
• Cell growth

Question 32

Why is cell size limited?

Answer 32

• Cell size is limited because of requirements for homeostasis (exchanges of gases, nutrients, waste through the plasma membrane of the cell)
• Metabolic demands: determined by volume, but transport of materials is determined by surface area
• Volume increases faster than surface area
• After a certain size, the cell membrane is not large enough to import enough material to meet the metabolic needs of the cell