Eukaryotes Flashcards
1
Q
Eukaryotes
A
- Eukarya
- Much more complex than prokaryotic cells
2
Q
Endosymbiont Theory
A
- 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
3
Q
Evidence of Endosymbiont Theory
A
- 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
4
Q
Cytosol
A
- The cytosol or cytoplasmic matrix is the liquid found inside cells
5
Q
Cytoplasm
A
- The area within the plasma membrane, which comprises of the cytosol, the mitochondria, plastids, and other organelles, but not the nucleus
6
Q
Endomembrane System
A
- 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
7
Q
Nucleus
A
- Stores the DNA
8
Q
Nuclear Envelope
A
- Defines the boundary of the nucleus
- Consists of two membranes (inner and outer) each is a separate lipid bilayer
- Also contains the nuclear pores
9
Q
Nucleous
A
- Appears as a mass of densely stained granules and fibers
- Site where rRNA is synthesized
- Assembly site of large and small ribosomal subunits
10
Q
Nuclear Pores
A
- Act as gateways allowing molecules to enter and leave the nucleus
11
Q
Ribosomes
A
- 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
12
Q
Endoplasmic Reticulum
A
- 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
13
Q
Rough Endoplasmic Reticulum
A
- Studded with ribosomes on the surface of the membrane
- Synthesis of proteins that are to be secreted
- Synthesis of membranes
14
Q
Smooth Endoplasmic Reticulum
A
- 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
15
Q
Golgi Apparatus
A
- 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
16
Q
Vesicles
A
- 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
17
Q
Lysosome
A
- 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)
18
Q
Phagocytosis
A
- 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
19
Q
Autophagy
A
- Lysosomes also use their hydrolytic enzymes to recycle the cell’s own organic material, a process called autophagy
- “Self-eating”
- Cleaning up the cell!
20
Q
Vacuoles
A
- Large vesicles derived from the endoplasmic reticulum and golgi apparatus
- Perform a variety of functions (food vacuole, contractile vacuole, central vacuole)
21
Q
Mitochondria
A
- 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)
22
Q
Chloroplast
A
- 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!)
23
Q
Thylakoid
A
- Internal membrane-bound compartments inside chloroplasts
- Thylakoid membrane contains specialized light-collecting molecules (such as chlorophyll II)
24
Q
Cytoskeleton
A
- 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
25
Microtubules
- 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
26
Centrosome
- 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
27
Microfilaments
- 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
28
Myosin
- 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
29
Intermediate Filaments
- 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
30
Cell Adhesion
- 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
31
Extracellular Matrix
- 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
32
Why is cell size limited?
- 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
