Cell structures Flashcards
Features of the nucleus
nuclear envelope surrounds
nuclear pores perforate envelope
contains DNA organised into chromosomes
nucleolus - complex of rRNA and proteins - ribosoomes
Features of the nuclear envelope
Surrounds nucleus
Double membrane – each a lipid bilayer with proteins
Each membrane separated by a narrow space (20-40 nm)
Perforated by pore structures
Pore structures lined by pore complex which controls the entry and exit of proteins, RNA and macromolecules
What is the nucleolus made from?
rRNA (ribosomal RNA) and proteins
a region rather than bound
proteins come from the cytosol
Does every cell have a nucleolus?
only visible in non dividing cells (disappears during mitosis)
Sometimes there are two or more nucleoli - the number depends on the species and the stage of the cells cell’s reproductive cycle
what is the function of the nucleolus
synthesises ribosomal RNA from instructions in the DNA
Proteins imported from the cytosol are assembled with rRNA into the small and large units of the ribosomes
Ribosome subunits exit through nuclear pores to cytoplasm where they join to form a ribosome
Where are ribosomes made?
Ribosomes are synthesised in the nucleolus
In the nucleolus proteins and rRNA are assembled into large and small subunits of the ribosomes
Subunits are then exported through nuclear pores to the cytoplasm
Are ribosomes organelles?
Ribosomes are not membrane bound and so are not considered to be organelles
What is the nuclear lamina
The nuclear lamina is a netlike array of proteins filaments found on the nuclear side of the nuclear envelope
Maintain the shape of the nucleus
May help organise genetic material
what is the nuclear matrix
The nuclear matrix is a framework of protein fibres extending throughout the nuclear interior
May help organise genetic material
what is the function of ribosomes
protein synthesis
rRNAs carry out peptidyl transferase activity - protein synthesis
What is the structure of ribosomes
large and small units
Are ribosomes present in all cells
Eukaryotic cells have ribosomes
Prokaryotes have some ribosomes but they are smaller
cells that have high rates of protein synthesis have more ribosomes as well as prominent nucleoli e.g. pancreatic cells which need to produce a lot of insulin and other digestive enzymes
what is the difference between free and bound ribosomes
Free ribosomes are found floating in the cytosol
Bound ribosomes are attached to the ER or the nuclear envelope
Proteins made in free ribosomes function in the cytosol e.g. enzymes
Proteins made in bound ribosomes – used in membranes / lysosomes or exit the cell e.g. digestive enzymes
Bound and free ribosomes are structurally identical and can play either role at different times
What role do ribosomes play in carrying out genetic instructions?
Ribosomes translate the genetic message carried from the DNA in the nucleus by mRNA into a polypeptide chain
What cellular structures make up the endomembrane system?
Nuclear envelope Endoplasmic reticulum Golgi apparatus Lysosomes Vesicles and vacculoles Plasma membrane
where are bound ribosomes located
bound ribosomes are attached to the outside of the endoplasmic reticulum or the nuclear envelope
where are free ribosomes located
free ribosomes are located in the cytosol
What happens to proteins made in free ribosomes?
free ribosomes are suspended in the cytosol and most of the proteins they make are used within the cytosol for example enzymes that catalyse the first steps of sugar breakdown
what happens to proteins made in bound ribosomes
bound ribosomes (attached to ER and nuclear envelope) are inserted into membranes/ for packaging into certain organelles like the lysosomes or for export out of the cell
what is the structure of the ER
Network of membranous tubules and sacs called cisternae
The ER membrane separates the internal compartment of the ER – called the ER lumen (cavity) or cisternal space from the cytosol
The Er membrane is continuous with the nuclear envelope
what are cisternae?
Sacs in the ER
What is the ER lumen?
internal compartment of the ER
cisternal space
separated from cytosol
because the ER membrane is continuous with the nuclear envelope, the space between the two membranes of the envelope is continuous with the lumen of the ER
how are the nuclear envelope and the ER connected
the ER membrane is continuous with the nuclear envelope
the space between the two membranes of the nuclear envelope is continuous with the ER lumen
what are the two regions of the ER
smooth Er and rough ER
how are the smooth ER and rough ER different?
smooth ER lacks ribosomes
rough ER studded with ribosomes on the outer surface of the membrane
where are ribosomes found in the cell
ribosomes attach to the outer surface of the rough ER and also to the cytoplasmic side of the nuclear envelope
Free ribosomes also found in cytosol
what are the functions of the smooth ER
synthesis of lipids
metabolism of carbohydrates
detoxification of drugs and poisons
storage of calcium ions
what types of lipids are produced in the smooth ER
oils
steroids e.g. sex hormones
new membrane phospholipids
what are the functions of the rough ER?
aids in the synthesis of secretory and other proteins on bound ribosomes
adds carbohydrates to proteins to make glycoproteins
produces new membrane
how does the rough ER function in making secretory proteins
polypeptide chain forms from ribosome
enters the lumen and folds to functional shape
in the lumen carbohydrates are attached to form glycoproteins (enzymes built into the ER membrane)
ER membrane keeps new proteins separate from cytosol
ER makes vesicles
what are transport vesicles
Vesicles that transit from one part of the cell to another
transport vesicles bud off from a region of the rough ER called the transitional ER
after leaving the ER many transport vesicles travel to the golgi apparatus
what is the function of the golgi apparatus
modifies products of ER stores products sends products to other destinations receives and dispatches transport vesicles manufactures some macromolecules
what is the structure of the golgi apparatus?
group of associated flattened membranous sacs - cisternae (unlike ER these sacs are not connected)
membrane separates internal space from cytosol
what are the two sides of the golgi?
cis face - located near the ER / receiving vesicles containing ER products
trans face - shipping department - dispatches vesicles that pinch off and travel to other sites
How does the golgi function to modify products
products are modified as they move from the cis to the trans region
glycoproteins formed in the ER have their carbohydrates modified (glycosolation)
membrane phospholipids also altered
what macromolecules are made in the golgi apparatus?
many polysaccarides secreted by cells are made in the golgi e.g. pectins
how does the golgi sort products before dispatch
the golgi sorts products and targets them for various parts of the cell
attach molecular identification tags like phosphate groups
transport vesicles may have external molecules that recognise docking sites on the surface of organelles or on the plasma membrane
what is the structure of cell membranes
cell membranes consist of a double layer of phospholipids
hydrophillic parts are in contact with the aqueous solutions inside and outside the cell
hydrophobic parts are inside and not in contact with liquids
embedded within and attached to the surface are diverse proteins
How does the plasma membrane contribute to cellular metabolism
many enzymes built into membranes
what is the structure of a lysosome?
membranous sac filled with hydrolytic enzymes
how is a lysosome made
hydrolytic enzymes and lysosome membranes form in the rough ER
transferred to golgi for further processing
lysosomes bud from the trans face of the golgi
what is phagocytosis?
lysosomes digest (hydrolyse) materials taken into the cell
vacuole taken into the cell fuses with a lysosome whose enzymes digest the food
e.g. amoeba and other unicellular eukaryotes eat by engulfing smaller organisms - make vacuoles
some human cells carry out phagocytosis e.g. white blood cells destroy bacteria
what is autophagy?
lysosomes recycle intracellular materials / cell’s organic material
a damaged organelle or small amount of cytosol becomes surrounded by double membrane and the lysosome fuses with it
what is a vacuole?
large vesicle derived from the endoplasmic reticulum and golgi apparatus
part of the cell’s endomembrane system
compartment that has different conditions to cytosol
what are contractile vacuoles
unicellular eukaryotes living in fresh water
pump excess water out of the cell
maintain concentration of ions and molecules inside the cell
do plant and fungi cells have lysosomes?
No - enzymatic hydrolysis is carried out in vacuoles
what are the functions of vacuoles?
food particles - digestion contractile vacuoles act like lysosomes in plants - break down wastes in plants may store compounds - storage cell growth and protection
what is the central vacuole
found in plant cells
largest compartment in plant cells
contains cell sap (store of inorganic ions)
enlarge as the plant absorbs water
what are the distinctions between the rough and smooth ER?
presence of ribosomes on rough ER
both types of ER make phospholipids
membrane proteins and secretory proteins are produced on the ribosomes of the rough ER
the smooth ER functions in detoxification, carbohydrate metabolism and storage of calcium ions
how are mitochondria and chloroplasts similar
both convert energy to forms that cells can use for work
mitochondria - cellular respiration
chloroplasts - photosynthesis
what is evidence for the endosymbiont theory
both mitochondria and chloroplasts are bound by two membranes (in contrast to other organelles bound by single membrane)
both contain ribosomes
both contain circular DNA
both are autonomous organelles that grow and reproduce within the cell
what cells contain mitochondria
mitochondria are found in nearly all eukaryotic cells
some cells have one but more often a cell has hundreds
How many mitochondria in a cell
some cells have only one but most have hundreds or even thousands
how many a cell has depends on its level of metabolic activity
describe the membranes of the mitochondria
two membranes
each membrane is a phospholipid bilayer
outer membrane is smooth
inner membrane folded called cristae
intermembrane space is the space between the inner and outer membrane
mitochondrial matrix - the compartment enclosed by the inner membrane
what is cristae
infoldings of the mitochondria
what is the inner membrane space
the space between the inner and outer membranes of the mitochondria
what is the mitochondrial matrix
enclosed by the inner membrane of the mitochondria
contains different enzymes
contains mitochondrial DNA and ribosomes
enzymes that function in cellular respiration embedded into the inner membrane
why is the cristae folded?
gives a larger surface area for cellular respiration
what does a chloroplast contain?
a chloroplast contains chlorophyll (green pigment) along with enzymes and other molecules that function in photosynthesis
where are chloroplasts located
in leaves and other green parts of plants and algae
describe the structure of a chloroplast
two membranes separated by a narrow intermembrane space
inner membranes divide the chloroplast into 3 compartments -
intermembrane space
thylakoids (stacks called granum)
fluid outside the thylakoids called stroma - contains chloroplast DNA and ribosomoes
what is a plastid?
plant organelle
chloroplast is one kind of plastid
describe two characteristics shared by chloroplasts and mitochondria
both involved in energy production
both have multiple membranes that separate their interiors into compartments
both have inner membranes that give large surface area - cristae in mitochondria and thylakoids in chloroplasts
both have embedded enzymes
Do plant cells have mitochondria?
Yes
plant cells are able to make their own sugar by photosynthesis but mitochondria are needed to make ATP
are mitochondria and chloroplasts part of the endomembrane system
No
different structure to membranes - double membrane for mitochondria and chloroplasts / single for others
not derived from ER
what is a peroxisome
bound by s single membrane
contain enzymes for metabolism
different functions
cooperate with mitochondria and chloroplasts
what is the function of peroxisomes
remove hydrogen atoms from various substrates and transfer them to oxygen producing hydrogen peroxide
peroxisoomes contain enzymes that convert hydrogen peroxide to water
what structures make up the cytoskeleton?
microtubules microfilaments and intermediate filament
what are the functions of the cytoskeleton?
structural support
maintain shape
provides anchorage for organelles
in some cells facilitates motility - changes in cell location and movement of cell parts
what is the structure of microtubules
globular proteins called tubulins
microtubules are hollow rods made of tubulin protein subunits
describe tubulin
hollow tubes
a dimer made from alpha tubulin and beta tubulin
what is a dimer
a molecule made up of two components
what is the function of microtubules
shape cell
support cell
tracks along which motor proteins can move - guide vesicles from the ER to Golgi and from golgi to plasma membrane
microtubules are also involved in the separation of chromosomes during cell division
cilia and flagella
what is a centrosome?
microtubules grow out of the centrosome
located near the nucleus
what is a centriole
found within the centrosome (where microtubules grow)
nine sets of three microtubules arranged in a ring
what is a primary cilium?
in vertebrate animals almost all cells have a primary cilium
signal receiving antenna
how are cilia and flagella different
usually large numbers of cilia (except primary cilium)
usually only one or a few flagella
flagella are longer
different beating pattern
what is the structure of cilia and flagella
group of microtubules sheathed in an extension of the plasma membrane
9 doublets of microtubules in a ring with 2 in centre (9+2)
anchored by a basal body
dyneins (motor proteins) involved in movement
what are microfilaments made from
actin (also called actin filaments)
what is the role of microfilaments
support cell shape (network inside the plasma membrane)
cell motility - allow cell to contract e.g. amoeboid crawling / cytoplasmic streaming in plants
what are pseudopodia
some cells (amoeba and white blood cells) move along by crawling movement. The cell crawls along a surface by extending cellular extensions called pseudopodia and moving towards them made possible by microfilaments and myosin
what is cytoplasmic streaming?
in plant cells
circular flow of cytoplasm
made possible by microfilaments
speeds up the movement of organelles and the distribution of materials within the cell
what cells have intermediate filaments
only the cells of some animals including vertebrates
microtubules and microfilaments found in all eukaryotes
what is the role of intermediate filaments
play an important role in reinforcing cell shape and fixing the position of organelles (permanent framework for the cell)
sturdy and more permanents than microtubules and microfilaments
what brings about cell movement
interaction between actin filaments (microfilaments ) and myosin
e.g. muscle cells
amoeba movement (pseudopodia)
cytoplasmic streaming
what cells have cell walls
this is one feature that distinguishes plant and animal cells
prokaryotes fungi and some unicellular eukaryotes (protists)
functions of the cell wall
protects the plant cell
maintains its shape
prevents excessive uptake of water
hold the plant upright
what are cell walls made from
cellulose fibres embedded in other polysaccharides and proteins
in fungi - chitin
what is the structure of the cell wall
young plant cell secretes a thin and flexible cell wall (around one cell) called the primary cell wall
the primary cell walls of adjacent cells is glued together by the middle lamella (pectins)
when the plant stops growing it strengthens its cell wall by secreting hardening substances
what is the middle lamella
a layer of sticky polysaccharides (pectins) that glue the cell walls of plant cells together
what is the extracellular matrix
like the cell wall of animal cells
what is the extracellular matrix made of
glycoproteins - collagen
proteoglycans
proteins and sugars
what are integrins
cell surface receptor proteins
built into the plasma membrane
attach to microfilaments of the cytoskeleton
transmit signals between the extracellular matrix and cytoskeleton - can result in changes in cell behaviour
what is fibronectin
glycoproteins that attach cells to the extracellular matrix
bind to integrins
helps ECM to communicate with cell - mechanical signalling
what are plasmodesma
perforate cell walls
channels that connect plant cells
cytosol can pass through plasmodesma to other cells
water and some solutes can pass freely from cell to cell
what types of cell junctions exist in animal cells
tight junctions
desmosomes
gap junctions
what are tight junctions
plasma membranes of neighbouring cells are bound together by proteins
continuous seal
prevents leakage of extracellular fluid
e.g. skin cells are watertight
what are desmosomes
like rivets fasten cells together (hinges)
attach muscle cells to each other
what are gap junctions
found in animal cells
also called communicating junctions
provide cytoplasmic channels from one cell to an adjacent cell (similar to plasmodesma in plants)
allows ions, sugars, amino acids and other small molecules to pass
pores surrounded by membrane proteins
necessary for communication between cells in many types of tissues - heart/muscle/ animal embryos
what are membrane proteins and what are their function
proteins embedded in the plasma membrane or other cellular membranes
transport substances across membranes
conduct signals
e.g. proton pump / calcium channel / aquaporin
Which cells have ribosomes
all living organisms have ribosomes
Eukaryotic ribosomes are called 80s ribosomes
Prokaryotic (bacteria/archaea) ribosomes are 70s - smaller
Mitochondria in cells also have ribosomes - these are smaller than those in the cytoplasm and are made separately to them
s - relates to centrifugiing
what are cell wall’s made of?
primary cell wall - cellulose in a gel like matrix
secondary cell wall - cellulose and polysaccharides
which organisms have mitochondria
all eukaryotic cells
not in prokaryotes - they don’t have membrane bound organelles
what do mitochondria , chloroplasts and nuclei have in common
all have functional DNA
