Eukaryotic Cell Structure Flashcards
what are eukaryotic cells
eukaryotic cells have a more complex ultrastructure than prokaryotic cells
their cytoplasm is divided into membrane-bound compartments called organelles - bound by a single or double membrane
why is the compartmentalisation of eukaryotic cells advantageous
it allows
- enzymes and substrates to be localised and therefore available at higher concentrations
- damaging substances are separated (e.g: digestive enzymes)
- optimal conditions to be maintained for certain processes (e.g: pH for digestion)
- numbers and location of organelles can be altered depending on requirements of the cell
what structures do animal and plant eukaryotic cells share
- membrane bound organelles including a nucleus, RERs, SERs, golgi apparatus, vesicles, lysosomes, mitochondria, plasma membrane
- 80S ribosomes
- cytoskeletons, cytoplasm
what are some key differences between animal and plant cells
animal cells contain
- centrioles
- microvilli
plant cells contain
- cellulose cell walls
- large permanent vacuoles
- chloroplasts
what can eukaryotic cells do in complex multicellular organisms
become specialised for specific functions and have specific adaptations (cells can look very different in shape and in terms of what organelles it contains)
- e.g: rbs are biconcave and don’t have a nucleus
plasma membrane function
- lipid bilayer of phospholipids that functions as a barrier between aqueous solutions
- thin line surrounding the cell
- tends to show darker on micrographs (proteins)
- controls the exchange of materials between the internal cell environment and the external environment (partially permeable)
nucleus function
- where DNA is replicated and transcribed
- contains DNA as well as enzymes needed to make DNA
- contains chromatin (make chromosomes, which are made of linear DNA wound around histones)
- usually surrounded by endoplasmic reticulum
- stains dark but may have internally lighter areas (difference in density), darker regions are nucleoli - ribosome production
- double membrane with many pores (transport) - nuclear envelope
- pores allow for mRNA and ribosomes to travel out of the nucleus as well as enzymes and signalling molecules to travel in
- sphere-ish
- pores may be visible
rough endoplasmic reticulum function
- central role in the synthesis and transport of polypeptides
- bound 80S ribosomes which synthesise the polypeptide and release it to the inside of the RER
- series of connected, flattened membranous sacs, formed from folds of membrane continuous with nuclear envelope
- usually found near the nucleus (amount depends on cell type)
- ribosomes on RER process material from the nucleus to make proteins
- proteins move from ribosomes to cisternae, then bud off to vesicles that carry then to golgi apparatus before being secreted out of the cell
smooth endoplasmic reticulum function
- central role in the synthesis of phospholipids and cholesterol
- for the formation and repair of membranes
- series of connected, flattened, membranous sacs
- usually found further from the nucleus that RER
- visible as pockets
- don’t synthesise proteins!!!
free ribosomes function
- synthesise polypeptides during translation to become proteins that function WITHIN the cell
- often the smallest structure in an electron micrograph
- found freely in cytoplasm of all cells
- complex of ribosomal RNA and proteins, constructed in the nucleolus
- made of 2 subunits (60S and 40S)
- site of translation
mitochondria function
- adapted for the production of ATP by aerobic cellular respiration
- evolved from prokaryotic cells
- bound by a double membrane
- circular or oval
- stain dark
- have infoldings of inner membrane called cristae
- matrix is formed by cristae - contains enzymes needed for aerobic respiration, like a cytoplasm
- small bits of DNA and ribosomes found in the matrix
golgi apparatus function
- modifies polypeptides (proteins and lipids) into their functional state
- sorts, concentrates and packs proteins into vesicles to be transported
- flattened stacks with a clear inside, made of cisternae
- proteins that go through the golgi apparatus are usually exported (e.g. hormones such as insulin), put into lysosomes (such as hydrolytic enzymes) or delivered to membrane-bound organelles
- have vesicles on their ends
vesicles function
- contain/store and transport materials within cells
- membrane bound
- circular
- stain dark (proteins stored)
- may be clumped to one side in secretory cells
- membrane fuses with plasma membrane for out and in transport
lysosome function
- specialist form of vesicles which contain hydrolytic enzymes (break down bio molecules)
- degrade and eject or recycle waste materials such as worn out organelles or pathogens that have been engulfed by phagocytes
- used by cells of the immune system and in apoptosis (programmed cell death)
- small spherical organelles
chloroplasts function
- adapted for photosynthesis (light energy and water and carbon dioxide –> glucose)
- bound by a double membrane
- in plant cells
- membrane-bound compartments called thylakoids containing chlorophyll stack to form structures called grana
- grana are joined together by lamellae (thin and flat thylakoid membranes)
- site of photosynthesis: light-dependent stage takes place in the thylakoids, light-independent stage (calvin cycle) takes place in the stroma
- also contain small circular pieces of DNA and ribosomes used to synthesise proteins needed in chloroplast replication and photosynthesis
large permanent vacuoles function
- stores water and/or metabolic waste
- plant cells: maintains turgor pressure
- bound by a single membrane: tonoplast
- clear (fluid inside)
- fill most of plant cell
- have cell sap
cell wall function
- extra-cellular component (not an organelle)
- fungi and plant cells
- helps develop turgor pressure
- protects the cell
- external to plasma membrane, offers structural support
- thicker line, light grey colour
- structural support given by cellulose (plants) and peptidoglycan in bacterial cells
- narrow threads of cytoplasm (surrounded by a cell membrane) called plasmodesmata connect the cytoplasm of neighbouring plant cells
flagellum function
- found in specialised cells
- similar in structure to cilia, made of longer microtubules
- long protrusion of cell membrane
- usually only 1-2 present
- microtubules in a 9+2 pattern
- contract to provide cell movement through a solution (e.g: sperm cells)
centrioles function
- hollow fibres made of microtubules (filaments and proteins) that can expand and contact
- two centrioles at right angles to each other form a centrosome which organises the mitotic spindle fibres during cell division
- serve as anchor points for microtubules in the cytoplasm and for cilia and flagella (when modified to become a basal body)
- paired, cylindrical
- 9 groups of 3 microtubules organised with radial symmetry
- not found in flowering plants and fungi
microtubules/cytoskeleton function
- makes up the cytoskeleton of the the cell, about 25 nm in diameter
- made of α and β tubulin combined to form dimers, the dimers are then joined into protofilaments
- thirteen protofilaments in a cylinder make a microtubule
- the cytoskeleton is used to provide support and movement/division abilities to the cell, it helps to organise cell parts
- long fibrous strands
- stained using fluorescence
microvilli function
- cell membrane projections
- used to increase the surface area of the cell surface membrane → +SA → + rate of exchange of substances
- shorter and more tightly packed than cilia
- do not have a 9+2 arrangement of microtubules
cilia function
- hair-like projections made from microtubules
- allows movement of substances over cell surface
- move regularly back and forth, can move cell or things across the cell surface
- microtubules arranged in a 9+2 pattern
- dark centre - microtubules
draw a plant and an animal eukaryotic cell
see photo flash cards