Cells, cell junctions, transport Flashcards
Define eukaryotic cell.
Eukaroyte cells have membrane bound organelles, linear DNA found in nucleous, DNA with intrones and exones bound on histone proteins.
Why are cells the fundamental building blocks of life?
the basic structural, functional, and biological unit of all known living organisms
Give 2 functions of the Golgi-apparatus.
Transport of lipids from smooth ER and proteins from rough ER. Modification of proteins such as phosphorylarion and glucosylation.
Which cell organelles are surrounded by a double membrane layer?
Mitochondria has smooth outer layer and folded inner layer.
What are the similarities and differences between a lysosome and a peroxisome?
Lysosome breaks down macromolecules (intracellular digestion)
Peroxisome is a membrane-bound organelles (excreted
by Golgi) that contain enzymes for
oxidation (oxidase) of amino acids and
detoxifying (catalase) harmful
substances
deals with free radicals, has catalase and peroxidase.
What are the main functions of the cytoskeleton? Describe its composition.
Actin filament, long peptides. Microtubule which can act as intracellular transport but costs ATP. Important for cilia and flagella. Intermediate filaments tough and can link organelles, cells and to the extracellular matrix.
• highly dynamic structure • 3 different filament types • mechanical strength • responsible for cell shape and movements/transport
Define nuclear lamina.
meshwork of nuclear
intermediate filament proteins that supports
and strengthen the nuclear envelope
What is a motor protein?
Dynein and kinesin
Drive intracellular transport
Move in opposite directions
Play an important role in movement and positioning of organelles within eukaryotic
cell –e.g. during cell division and nerve cells
How does skeletal muscle contraction work?
Actin filaments slide against myosin filaments
shortening of sarcomeres without changing the length of each
filament
(Which cell organelles are present in a plant cell but not in an animal cell? What is the function of these organelles?)
Chloroplast: photosynthesis: sunlight to glucose
What are cell membranes made of? How are these components arranged?
Lipid bilayer with hydrophilic heads and hydrophobic tails, hydrophilic heads out
Describe the composition of a phospholipid.
molecule has a hydrophilic “head” containing a phosphate group and two hydrophobic “tails” derived from fatty acids, joined by an alcohol residue
Why has a cell a lipid bilayer?
Physical and protective barrier •Regulate transport •Allow cell-recognition and cell communication •Mechanical properties • continuity • capacity for movement and expansion •Internal membrane (eukaryotes) • enclosing an intracellular compartment • differences in protein membranes –responsible for giving each organelle its distinctive character
Bilayers spontaneously close in on themselves to form sealed
compartments = energetically most favourable
Which molecule plays an important role in membrane fluidity?
fluidity modulated by cholesterol
Cholesterol makes the bilayer stronger, but less fluid and less permeable
unsaturation makes bilayer more fluid
Review how lipids move in the bilayer.
lateral diffusion, flexion, rotation, flip flop (last one is rare)
How can the fluidity of a cell membrane be changed?
More cholesterol
lenght and grade of saturation
how closely packed it is
What are the functions of membrane proteins?
Transport, receptor, enzyme, anchor
What kind of membrane transport proteins do exist?
Transporter (binding site, high specificity)
Channel (pore, discriminate on size and electrical charge)
Define glycocalyx and describe its function.
carbohydrate layer, sugar coat on extracellular site of lipid bilayer.
Protection cell surface from mechanical and chemical damage/stress
• Example: water-absorbing sugars give a slimy structure that helps
motility and prevents sticky cells
• Important in cell-cell recognition and cell-adhesion
• Example: lectin recognizes specific glycocalyx on neutrophils
What is the difference between active and passive transport? Give an example of each type.
Active transport against concentration gradient and requires ATP. Eg. transport of glucose. Passive transport does not require ATP, can be channel mediated or transporter mediated. Aquapourins allow water to flow through, a passive transport.
Describe the working mechanism of Na/K pump?
An electrogenic transmembrane ATPase.
The Na⁺/K⁺-ATPase enzyme is active (i.e. it uses energy from ATP). For every ATP molecule that the pump uses, three sodium ions are exported and two potassium ions are imported; there is hence a net export of a single positive charge per pump cycle.
Define symporter, antiporter, and uniporter.
Draw a neuron and label the cell body, axon, dendrite, and nerve terminal.
Looks like a tree, in which tree top is cell body, trunk is axon and roots are terminal branches. Dendrites are branches on the tree.
Describe the process of nerve cell signalling.
Action potential, nerve impulses. A travelling wave on the axon. Ion channels in axon are voltage gated. Wave of depolarisation.
Why is action potential referred as “all-or-none”?
If a stimulus is strong enough, an action potential occurs and a neuron sends information down an axon away from the cell body and toward the synapse. … The action potential is always a full response. There is no such thing as a “strong” or “weak” action potential. Instead, it is an all-or-nothing process
Which type of membrane proteins (channel) in the nerve terminal will be activated by a
nerve impulse?
Voltage gated Ca2+ channels in nerve terminals
convert electrical signal into a chemical signal
Transmitter-gated ion channels at postsynaptic cell gives
electrical signal
What is a protein signal sequence?
to direct the protein
to a particular destination
eg. ER signal sequence
Describe protein transport through nuclear pores.
Meshwork of proteins: small water-soluble molecules can pass the nuclear pore (unselective). Larger molecules and macromolecular complexes: • Nuclear localisation signal recognized by nuclear import receptor • Requires energy (GTP) • Fully FOLDED conformation
Give the differences and similarities between protein transport through the membrane of the
nucleus and the mitochondria.
Through membrane to nucleus occurs fully folded. Through membrane on mitochondria and chloroplasts unfolded. Chaperone helps to fold corrected when entered.
What is a protein translocator?
Protein translocators are proteins on inner membrane of mitochondria and chloroplast
How are water-soluble proteins (made on the ER) released in the ER lumen?
SRP signal recognition particle binds to ER sequence and ribosome. Ribosomes move to translocator and release SRP. Synthesised into ER lumen.
