Eukaryotes Flashcards
Eukaryotes
Protists, fungi, animals and plants all consist
of eukaryotic cells
Eukaryotes vs. Prokaryotes:
Similarities
Both have plasma membranes enclosing
them, cytosol, DNA and proteins
Eukaryotes vs. Prokaryotes:
Differences
• Location of DNA o Eukaryotes: located in nucleus with a double membrane o Prokaryotes: concentrated in a region not membrane bound called nucleoid
• Cytoplasm:
o Eukaryotes have a variety of organelles
of specialized form and function
o Prokaryotes have organized regions
• Eukaryotes are larger -> can carry out more
functions
Compartmentalisation and the Endomembrane
system
• Eukaryotic cells have an elaborate and extensive
internal membrane system
• This divides cell into compartments
• Compartmentalization provides different local
environments for specific metabolic reactions to occur
o Incompatible processes can occur at the same
time
• Plasma membranes and organelle membranes also
participate in the cell’s metabolic activities as well as a
variety of functions based on the composition of the
membranes -> See cell membrane section
• Membranes in this system may be related through
direct physical continuity, or by transfer of membrane
segments (vesicles)
• However, the various membranes are not identical
Parts of endomembrane system:
- Nuclear envelope
- ER (rough and smooth)
- Lysosomes
- Vesicles that bud off ER
- Golgi body
- Vesicles that bud off Golgi
- Plasma membrane
Cell nucleus and nuclear envelope
• Nucleus contains most of the genes in the eukaryote à some found in mitochondria • 5μm in diameter • Nuclear envelope encloses the nucleus, separating its contents from cytoplasm o Has a double membrane o Each a lipid bilayer o Contains pores for exit and entry of RNAs and proteins
• Nuclear lamina maintains shape of nucleus • Within nucleus DNA is organized into chromosomes à carries genetic info o Chromosomes are made up of DNA strand wrapped around a core of proteins o Together chromosomes for the chromatin network o Chromosomes are only distinguishable during cell division
• Nucleolus
o Synthesis of mRNA occurs
o Assembly of ribosomes
Overall functions of nucleus
• Carries hereditary information
• Controls all activities of the cell
Ribosomes
• Ribosomes are the protein factories of cells • Made from mRNA and protein • Not an organelle as does not contain membrane • Aids in protein synthesis • Are either free (suspended in cytosol) or bound (attached to outside of ER) • Type of ribosome determines the functioning of the protein created
The endoplasmic reticulum
• ER is an extensive network of membranes that accounts for half of the total membrane in eukaryotic
cells
• Endoplasmic -> inside the cytoplasm
• Reticulum -> little net(work)
• Consists of a network of membranous tubules and sacs called cisternae
• ER membrane separates the internal compartment of the ER (lumen/cisternal space) from the cytosol
• ER is continuous with nuclear envelope, therefore, space between two membranes of envelope is
continuous with lumen
• Two distinct but connected regions of ER:
o Smooth ER -> smooth outer surface that lacks ribosomes
o Rough ER -> rough outer surface studded with ribosomes
Smooth ER
Functions
• Synthesis of lipids (oils, phospholipids and
steroids (and hormones))
o Made by enzymes of smooth ER
o Sex hormones produced as well as steroid of
adrenal glands
• Metabolism of carbohydrates
o Enzymes covert glycogen into glucose used
in cellular respiration
• Detoxification of poisons à liver
o Drug enters body, Smooth ER detoxifies it by
adding a hydroxyl (OH) group onto drug,
making it soluble, making it easier to be
flushed from body
o Results in the proliferation of smooth ER à
large amounts of smooth ER produced à
faster right of detoxification
o Results in an increase in drug tolerance,
therefore, higher doses required to achieve
same effect
• Stores calcium ions in muscle cells
o Aids in muscle contraction
Rough ER
Functions
• Synthesis of secretory proteins by ribosomes attached to rough ER o Cell then secretes these proteins o E.g. secretion of insulin protein by pancreas into bloodstream • Membrane factory for cell o Grows by adding membrane proteins and phospholipids to its own membrane
The Golgi Apparatus
• Secretory proteins depart from ER wrapped in membranes of vesicles that bud from the region
called the transitional ER
o These are known as transport vesicles
• Some of these vesicles travel to the Golgi body
• At the Golgi body products of the ER (such as proteins) are modified and stored before being sent to
other destinations
• Golgi apparatus consists of flattened membranous sacs (cisternae), looking like a stack
• There are many stacks of Golgi present in cells that are specialized for secretion of proteins
• Separation of internal space of cisternae from cytosol by membrane
• The membranes of cisternae on either side of the stack differ in thickness and molecular
composition
• The two sides of a Golgi stack have distinct polarity and are known as the cis and trans regions
• Cis = receiving end (usually closer to ER)
o Transport vesicles add their membranes and the contents of their lumen to the cis by fusing
with Golgi membrane
• Trans = transport/shipping end
o Gives rise to vesicles that pinch off and travel to other sites
• The products of ER are modified during the transition through Golgi body, from the cis to the trans
ends
Lysosomes
• A lysosome is a membranous sac of hydrolytic enzymes that many eukaryotic cells use to digest
macromolecules
• Lysosomal enzymes work best in acidic environments such as the one found in lysosomes
o If lysosome bursts, the enzymes are inefficient due to the neural pH of cytosol
o Excessive leakage can destroy a cell by self digestion
• Lysosomes and their contents are made by rough ER and then transferred to Golgi apparatus for
processing
o Some arise from the budding off the trans face of the Golgi body
• Lysosomes carry out intercellular digestion in a variety of circumstances, for example during
phagocytosis, the food vacuole fuses with the lysosome, whose enzymes digest the food
o Digestion products then move into the cytosol and are used as nutrients
o Human cells that carry out phagocytosis are white blood cells (macrophages)
• Lysosomes also undergo a process known as autophagy -> where the cell’s own organic material is
recycled
o Damaged organelles are fused with the lysosome where they are broken down and the
products released back into the cytosol for reuse
o In this way cell constantly renews itself -> liver cells in humans
• Inherited lysosomal storage disease lack functioning hydrolytic enzymes -> indigestible material
interferes with cell activities
o Tay Sachs (non-functional hydrolytic enzymes – brain becomes impaired due to accumulation
of lipids in cells)
Mitochondria & Chloroplasts
• Considered separate from endomembrane system -> no connected physically or by means of
vesicles to endomembrane system
• Both organelles enclosed by membranes (at least two membranes)
• Contain their own DNA that encodes some of their proteins
• Semi-autonomous -> grow and reproduce within cell
• Covert energy to forms that the cells can use
• Mitochondria are the sites of cellular respiration, the metabolic process that uses oxygen to drive
the generation of ATP by extracting energy from sugars, fats, and other fuels
• Chloroplast are involved in photosynthesis -> solar into chemical energy
The Cytoskeleton
• Cytoskeleton -> network of fibres that extends throughout the cytoplasm
o Involved in maintaining and organizing structure of cell
• Cytosol -> h2O and dissolved ions, proteins, carbohydrates, nucleic acids
Roles of cytoskeleton
• Mechanical support -> maintains shape
oImportant in animal cells due to lack of cell wall
• Provides anchorage for cell organelles
• Dynamic structure
oCan be disassembled, or de-polymerized, in one part of the cell and then reassembled in
another part -> Changes shape of cell
• Involved in cell motility -> changes to cell location and movement of cell parts
oRequires interaction between cytoskeleton elements and motor proteins
oAbove two work with plasma membrane and cause cells to move along fibre networks outside
of cell
oInside cells organelles and vesicles often use motor proteins to walk along tracks provided by
cytoskeleton to their destinations
