3.2 Eukaryotic Cells Flashcards
What is a eukaryotic cell?
a cell that contains a nucleus and other organelles
What is the plasma membrane (cell membrane) composed of?
phospholipid bilayer embedded with protein molecules
What is the function of the plasma membrane (cell membrane)? (2)
- a living boundary that separates the living contents of the cell from the surrounding environment
- regulates the passage of molecules into and out of cells
What is cytoplasm?
a semi-fluid medium inside the cell composed of water, salts, and dissolved organic molecules
What is the cell wall composed of?
polysaccharides
What is the function of the cell wall?
support and protection
What is the cell wall?
a permeable but protective wall in plant cells in addition to the plasma membrane
most plant cells have both a primary and secondary cell wall
What is the main constituent of the primary cell wall?
cellulose
What does cellulose do in the primary cell wall?
form fibrils that lie at right angles to one another for added strength
What is the secondary cell wall?
- if present, it forms inside the primary cell wall
- contains lignin which is a substance that makes them even stronger than primary cell walls
What are the cell walls of fungi composed of?
cellulose and chitin
What is chitin?
a polysaccharide found in the exoskeleton of insects
What are the cell walls of algae composed of?
cellulose
What is an organelle?
a well-defined subcellular structure that performs a particular function
What did the term organelle originally refer to?
only membranous structures
What are some cell structures that are found in animal cells, but not in plant cells?
- lysosomes (not commonly found)
- centrioles
What are some cell structures that are found in plant cells, but not in animal cells?
- central vacuole
- chloroplast
- cell wall (not an organelle that is INSIDE cells)
What is the nucleus composed of?
nuclear envelope
nucleoplasm
chromatin
nucleoli
What is the function of the nucleus?
- stores genetic material (DNA)
- synthesizes DNA and RNA
What does DNA contro?
the characteristics of the cell and its metabolic functions
All individuals contain the same DNA but why are we all different?
which genes are turned on and which are turned off differs among cells
What is chromatin?
consists of DNA and associated proteins within a cell
What does chromatin become and how?
CHROMOSOMES
chromatin in most eukaryotic cells is not one continuous strand
during most of the cell’s lifetime, chromatin is present but when the cell is ready to undergo cell division, it will undergo coiling and become highly condensed structures called chromosomes
What are chromosomes?
highly condensed structures with 46 in human cells that are immersed in neoplasm
What is neoplasm?
semifluid medium within a cell’s nucleus
What suggests that the nucleoplasm has a different composition
a difference in pH between the nucleoplasm and the cytoplasm
What is the composition of nuceloli?
concentrated area of chromatin, RNA, and proteins
What is the function of the nuceloli?
- rRNA (ribosomal RNA) synthesis
- rRNA joins with proteins to form the subunits of ribosomes
What is the nuclear envelope?
double membrane that separates the nucleus from the cytoplasm and is continuous with the ER
What is a nuclear pore?
a pore in the nuclear envelope to permit the bidirectional transport of proteins and ribosomal subunits
What happens to the nuclear envelope during cell division?
completely disappears and the contents of the nucleus are mixed with the cytoplasm
What happens to the nuclear envelope after cell division?
it re-forms around the chromosomes and the other contents of the nucleus are transported into the nucleus
What are ribosomes responsible for?
the synthesis of proteins using messenger RNA as a template
What are ribosomes composed of?
2 subunits called “large” and “small” because of their relative sizes
each subunit is a complex of unique ribosomal RNA (rRNA) and protein molecules
Where can ribosomes be found?
- individually in the cytoplasm
- in groups called polyribosomes
- attached to the ER
What is a polyribosome?
several ribosomes associated simultaneously with a single mRNA molecule
Where do synthesized proteins in ribosomes go?
proteins synthesized at ribosomes attaches to the ER have a different destination from that of protein synthesized at ribosomes free in the cytoplasm
What does the endomembrane consist of?
- nuclear envelope
- ER
- Golgi apparatus
- several vesicles
What are vesicles?
tiny membranous sacs
What is the endomembrane system?
transportation and processing part of the cell
compartmentalizes the cell so that particular enzymatic reactions are restricted to specific regions
How are the organelles that make up the endomembrane system connected?
directly or by transport vesicles
What is the endoplasmic reticulum?
a complicated system of membranous channels and sacs (flattened vesicles) and is physically continues with the outer membrane of the nuclear envelope
What is the function of the ER?
synthesis and/or modification of proteins and other substances, and distribution by vesicles formation
What is rough ER?
network of folded membranes studded with ribosomes on the side that faces the cytoplasm
What are the proteins formed in the ER for?
- membrane of the cell
- to be secreted from the cell
What is critical to the function of the cell regarding proteins?
proper folding, processing, and transport of proteins
What happens in cystic fibrosis regarding the ER?
a mutated plasma membrane channel protein is retained in the end plastic reticulum because it is folded incorrectly
without this protein in it’s correct location, the cell is unable to regulate the transport of the chloride ion, resulting in symptoms of cystic fibrosis
What is the structure of smooth ER?
network of folded membranes with no ribosomes
What does the smooth ER do?
synthesized the phospholipids found in cell membranes
detoxification reactions
various:
- in testes: produces testosterone
- in liver: helps detoxify drugs
- in muscle cells: stores calcium ions
also forms vesicles in which products are transported to the Golgi apparatus
What is the structure of the Golgi apparatus?
consists of a stack of 3 to 20 slightly curved small membranous sacs
What is the function of the Golgi apparatus?
collects, sorts, packages, and distributed materials such as proteins and lipids
Where are vesicles in the Golgi apparatus?
can frequently be seen at the edges of the sacs
In animal cells, what is the orientation of the stacked sacs in The Golgi apparatus?
one side of the stack (inner face) is directed toward the ER, and the other side of the stack (the outer face) is directed towards the plasma membrane
What does the Golgi apparatus receive?
protein and lipid-filled vesicles that bud from the ER
What happens to the proteins and lipid-filled vesicles received by the Golgi apparatus?
these molecules move through the Golgi from the inner face to the outer face
What is secretion?
during molecules’ passage through the Golgi apparatus, proteins and lipids can be modified before they are repackaged in secretory vesicles
secretory vesicles proceed to the plasma membrane where they discharge their contents
What else is the Golgi apparatus involved in?
the formation of lysosomes
What do the proteins made at the rough ER do?
have specific molecular tags that serve as “postal codes” to tell the Golgi apparatus whether the belong inside the cell ins one membrane-bound organelle or in a secretory vesicle
What are lysosomes?
membrane-bound vesicles produced by the Golgi apparatus that contain hydrolytic digestive enzymes
How can macromolecules sometimes be brought into the cell?
by vesicles formation at the plasma membrane
What happens when a lysosomes fuses with a vesicle?
it’s contents (ie. bacteria, parts of a cell: AUTODIGESTION) are digested by lysosomal enzymes into simpler subunits that then enter the cytoplasm
How do some white blood cells defend the body?
by engulfing pathogens via vesicle formation
What happens in Tay-Sachs disease?
the cells that surround nerve cells cannot break down the lipid gamglioside GM2, which then accumulated inside lysosomes and affects the nervous system
at about 6 months, the infant can no longer see and then gradually loses hearing and even the ability to move
death follows at about 3 years of age
What is a vacuole?
a large membranous sac (larger than a vesicle)
What cells have vacuoles?
although animal cells have vacuoles, they are much more prominent in plant cells
What is a central vacuole?
plant cells have a large central vacuole filled with a watery fluid that provides added support to the cell
What is the function of vacuoles?
stores substances
- water
- sugars
- salts
plant cells also contain pigments and toxic molecules
What are pigments responsible for?
the colours of flowers and leaves
What are the toxic substances responsible for?
help protect a plant from herbivorous animals
What do the specialized vacuoles in unicellular protozoans do?
they include
- contractile vacuoles for ridding the cell of excess water
- digestive vacuoles for breaking down nutrients
Describe the endomembrane system.
- incoming vesicle brings substances into the cell that are digested when the vesicles fuses with a lysosome
- lysosome contains digestive enzymes that break down worn-out cell parts or substances entering the cell at the plasma membrane
—————
- smooth ER synthesized lipids and also performs various other functions
- transport vesicle shuttles lipids to various locations such as the Golgi apparatus
—————
- rough ER folds and processes proteins and packages them in vesicles (vesicles commonly go to Golgi apparatus
- transport vesicle shuttles proteins to various locations such as the Golgi apparatus
—————
- Golgi apparatus modifies lipids and proteins from the ER sorts them and packages them in vesicles
- secretory vesicle fuses with the plasma membrane as secretion occurs
What are peroxisomes?
similar to lysosomes, are membrane-bound vesicles the enclose enzymes
Where are the enzymes in peroxisomes synthesized?
by cytoplasmic ribosomes and transported into a peroxisomes by carrier proteins
Typically, peroxisomes contain enzymes whose action results in what?
hydrogen peroxide H2O20
RH2 + O2 —> R + H2O2
(R = remainder of molecule)
What is catalase?
a peroxisomes enzyme that immediately breaks down hydrogen peroxide into water and oxygen
What do peroxisomes do?
various metabolic tasks
liver: break down fats or produce bile from cholesterol
Where are the enzymes in peroxisomes found?
depends on the function of the cell, they are prevalent in cells that are synthesizing and breaking down fats
What happens in ALD disease?
cells lack a carrier protein to transport an enzyme into peroxisomes resulting in a long-chain fatty acid accumulating in the brain and neurological damage
Give an example of peroxisomes in plant cells.
- in germinating seeds: oxidize fatty acids into molecules that can be converted to sugars needed by the growing plant
- in leaves: can carry out a reaction that is opposite to photosynthesis, the reaction used up oxygen and releases carbon dioxide
Why is life possible?
because of a constant input of energy that organisms use for maintenance and growth
What are the 2 eukaryotic membranous organelles that specialize inc converting energy to a form the cell can use?
chloroplasts and mitochondria
What is the structure of chloroplasts?
bounded by 2 membranes that enclose a fluid-filled space called the stroma
What is the function of chloroplasts?
allows photosynthesis
What is photosynthesis?
solar energy + co2 + h2o —> carbohydrate + oxygen
What is the structure of the mitochondria?
inner membrane (cristae) bounded by an outer membrane
What is the function of the mitochondria?
cellular respiration
break down the carbohydrates synthesized by chloroplasts to produce ATP molecules
What is cellular respiration?
carbohydrate + oxygen —> co2 + h2o + energy (ATP)
What is ATP used for?
all energy-requiring processes in cells
Where do chemicals recycle?
between chloroplasts and mitochondria in the presence of solar energy
What happens when cells use ATP?
energy dissipates as heat, most life cannot exist without a constant input of solar energy
How do cyanobacteria carry out photosynthesis?
within independent thylakoids
What organisms complete the process of cellular respiration in mitochondria?
all organisms except prokaryotes
What are plastids?
a certain group of organelles that also contain
- amyloplasts: common in roots which store starch
- chromoplasts: common in leaves which contain red and orange pigments
Why is chloroplast green?
contains the green pigment chlorophyll, a typical plant cell in a leaf may contain ~50 chloroplasts
How do chloroplasts divide?
by splitting in 2 in a manner similar to how bacteria divide
What does the stroma contain?
a single circular DNA molecule as well as ribosomes
What does chloroplast contain?
its own genetic material
Do chloroplasts make proteins?
they make most of their own proteins while others are encoded by nuclear genes and imported from the cytoplasm
How is a membrane system within the stroma organized?
into interconnected flattened sacs called thylakoids
in certain regions, the thylakoids are stacked up in structures called grana
there can be hundreds of grana in a single chloroplast
Where is chlorophyll located?
within the thylakoid membranes of grana
What does chlorophyll do?
captures the solar energy needed to enable chloroplasts to produce carbohydrates
solar energy excites an electron within the chlorophyll molecule and the energy from the electron is used to make high energy compounds
What is the the mitochondria?
the power house of the cell
What happens to subtrates broken down in the cytoplasm?
transported into the mitochondria and converted into ATP to be used by the cell for its various needs
What else are mitochondria involved in?
cellular differentiation and cell death (aging)
How do mitochondria divide?
by splitting in 2
they are bounded by a double membrane
What is the matrix?
the inner fluid-filled space in mitochondria
Do mitochondria make proteins?
like chloroplasts, they contain their own circular DNA chromosome and encode some, but not all of their own proteins
What does the matrix contain?
ribosomes and enzymes that break down carbohydrate products, releasing energy to be used for ATP production
How is the cristae formed?
the inner membrane of a mitochondrion folds inward on itself
What does cristae provide?
a much greater surface area to accommodate the protein complexes and other participants that produce ATP
What do mutations in the mitochondrial DNA usually effect?
high-energy-demand tissues such as the eye, central nervous system, and muscles
What has made mitochondrial DNA studies useful for population genetic studies?
in humans, all mitochondria come from the mother’s egg. the father’s sperm does not contribute any mitochondria to the offspring
