Unit 2 Chapter 7: Cells Flashcards
What are chromosomes (in prokaryotes)
- the most prominent structure in bacterial cells
- usually have 1 circular one (large DNA molec with some proteins)
How does DNA fit into small cells
DNA double helix coils on itself with the help of enzymes to form the highly compacted “super coil structure”
Where are bacterial chromosomes found
in the nucleoid (usually in center/20% of cells volume)
NOTE: nucleoid is enclosed by a membrane
What are plasmids (prokaryotes)
small, circular, usually super-coiled DNA molecs found in bacteria that contain genes but are physically independent of the main circular chromosome
-can be considered auxiliary genetic elements as the genes inside them are not usually required
What are ribosomes
- structures that manufacture proteins
- in bacteria they contain RNA and proteins
Describe the photosynthetic membranes in prokaryotes
- contain the enzymes and pigment molecs required for photosynthesis to occur and develop as infoldings of the plasma membrane
- sometimes vesicles pinch off as membrane folds in
- sometimes flattened stacks of photosyn membrane form the infolds in the plasma membrane
- large surface area allows for more reactions to occur
What are 4 key tasks of bacterial organelles
- storing calcium ions or other key molecs
- holding magnetite crystals which act as a compess and sense a magnetic field and swim in a directed way
- organizing enzymes in charge of making carbon compounds from CO2
- hiding enzymes that generate chemical energy from ammonium ions
What is the cytoskeleton (prokaryotes)
long thin fibres made of long polymers of globular proteins that serve as structural support
-responsible for shape, cell division, transport of plasmids and organization of cell interior
What are flagella (prokaryotes)
- enable species to swim by rotating like a propeller
- tail-like structure
- few in # and located on cell surface
- made of flagellin
- no membrane
Describe the structure and function of the cell wall in prokaryotes
- structure: tough, fibrous layer that surrounds the plasma membrane
- resists pressure that is exerted due to inward water flow from osmosis. protects cell and gives it shape and rigidity
Why is compartmentalization beneficial?
- incompatible chem reactions can be separated
- chemical reactions become more efficient
What is the nucleus
- brain of cell
- contains chromosomes and is the info storage and processing centre
- enclosed by a DOUBLE membrane
What is the nuclear envelope
double membrane that encloses nucleus and is studded with openings/inside surface is linked to fibrous proteins that form a sheet called the nuclear lamina
-continuous with endomembrane system
What does the nuclear lamina do
stiffens structure and maintains shape
Do chromosomes float freely in the nucleus
no, each has a distinct spot and is attached nuclear lamina in at least one spot
What is the nucleolus
distinct region in nucleus where RNA found in ribosomes are made and small ribosomal subunits are assembled
What is the ER
extensive series of membrane bound sacs extending from nuclear envelope into cytoplasm
What is the difference between smooth and rough ER
rough=has attached ribosomes that make proteins to be inserted into the plasma membrane, secreted to the outside of the cell or shipped to an organelle; rough ER products are packaged into vesicles and transported
smooth=no ribosomes, contains enzymes that catalyze lipid reactions, manufactures phospholipids, reservoir for Ca ions (signalling)
What is the golgi apparatus
flattened membranous sacs (cisterna) which are stacked
- organizes, packages and ships proteins (processing and sorting)
- cis-faces ER
- trans-faces membrane
What does the cis side of the golgi body do
receives products from rough ER
What dies the trans side of the golgi body do
ships the products away towards cell surface
What are ribosomes (eukaryotes)
made of 4 rRNAs and 80 proteins, make proteins, NOT classified as an organelle because not surrounded by a membrane
What are peroxisomes
globular organelles: contain enzymes, centres for oxidation reactions, have a single membrane and originate as buds from the ER
What are lysosomes
digestive centres
What is autophagy
- a damaged organelle is brought in and delivered to a lysosome
- its digested
- small molecs from the digestion are released into the cytosol
What is phagocytosis
cell eating
- plasma membrane detects a cell or particle and engulfs it creating a phagosome
- delivered to lysosome and digested
- small molecs from the digestion are released into the cytosol
What is pinocytosis
cell drinking
- fluid brought into cell via tiny vesicles that form infoldings of plasma membrane
- fluid used elsewhere in cell
What is receptor mediated endocytosis
think claw machine
- molec binds to membrane proteins that act like receports
- membrane folds off and pinches in to form an early endosome
- endosome undergoes processing ie;. activation of proton pumps that lower pH
- early endosome matures into a late one and recieves digestive enxymes from golgi body
- late endosome turns into lysosome
What are vacuoles
large storage depot usually for water or ions
What is the mitochondria
powerhouse of cell
- has 2 membranes
- contains DNA (chromosomes) which allows them to make some of their own proteins
- have own ribosomes
- plastids
- have cristae which increase SA to fill membrane with proteins and make ATP
What are chlroroplasts
- has DNA
- in plants, mature form of plastids, convert solar energy into chemical energy for photosynthesis
- has a double membrane
- thylakoids stacked into grana which are all in stroma
- larger than mitochondria
What is lignin
forms a branching cave like network that is impossible for enzymes to attack
in the secondary cell wall that some plants produce
Why are cells small
surface area to volume ratio, most reactions require diffusion and diffusing molecules don’t travel long distances due to their random walk
What is included in the endomembrane system
ER, golgi body, vesicles, nuclear and cell mebranes
What happens in the nucleus
DNA is replicated, DNA is transcribed in to mRNA and rRNA, mRNA is translated rRNA is not
Why is rRNA not translated
it directly folds into a 3D structure
What does the animal pancreatic cell do
exports digestive enzymes
What does the animal testis cell do
exports lipid soluble signals
What is the evidence that mitochondria and chloroplasts are descendants of bacteria (endosymbiont theory)
- double membrane
- own genome
- own ribosomes more similar to eubacteria
- genes more similar to eubacteria genes
What was the Pulse-Chase experiment
used to research the secretory path way:
pulse=expose exp. cells to a high concentration of a labelled molec for a short time
chase=larger amounts of unlabelled version of the same molec for a longer time
results support the secretory path way that proteins move from ER to golgi to secretetion
What is the signal hypothesis
- ribosome synthesizes ER signal sequence
- signal sequence binds to a signal recognition particl:SRP
- ribosome+SRP+ signal sequence attaches to SRP receptor in ER membrane
- once receptor and SRP connect, SRP is released
- signal sequence removed and protein synthesis is completed
What are the possible “fates” for proteins
stay in endomembrane system, sent to lysosomes, plasma membrane for exocytosis or outside of the cell
What are actin filaments and what is their function
-microfilaments
-made of actin
-polar, has a + and - end
-treadmilling=the addition or subtracting of actin molecs to each end (tend to grow at + end)
-structure resembles two long strands coiled around eachother
Function: structural support, cell shape by resisting tension, movement (myosin head binds to actin for movement), divide cells, move organelles
What are intermediate filaments and what is their function
- non-polar
- fibres wound into thicker cables
- purely for structure: resist tension (pull), anchor nucleus and organelles
- made of keratin, vimentin or lamin
What are microtubules
- hollow tubes of alpha and beta tubulin
- largest cytoskeletal components
- polar, usually grow at their + end
- originate from MTOC, which contains centrosome that contain 2 bundles of microtubules called called centrioles
- provide stability + movement via flagella/cilia, resist compression, move chromosomes during division, move organelles, intracellular transport, formation of cell plate in plant division
What happens if microtubules are prevented from forming
ER no longer assembles in its normal network-like config
What is kinesin
like actin it is a motor protein, which acts like a delivery truck to move transport vesicles down the microtubule tracks
-it “walks” along the tracks when it’s head region binds to ATP
What are flagella (eukaryotes)
- made of microtubules
- move cell by whipping back and forth
- plasma membrane
- evolved independently from bacteria flagella
- closely related to cilia
What is dynein
-a motor protein
-changes shape when phosphate from ATP binds to it
-change in shape moves molecule along microtubule
-when dynein reattaches it has succeeded in walking a step along the microtubule doublet
(allows microtubule doubles to slide past eachother)
-walks in opposite direction of kinesin
-bends cilia and flagella
What allows microtubules/axonemes to bend
if dynein arms on one side of axoneme walk and cause some doublets to slide while those on the other side are at rest
-in cilia/flagella this causes swimming
How are molecular postal codes read
they bind to receptor proteins
Where does translation always begin
in the cytosol
