B2.1 - 2.3 Bio Flashcards
What is the plasma membrane made of?
Bilayer of phospholipids and other amphipathic molecules form a continuous sheet to control the passage of substances
Phospholipid molecules
Phosphate head and two hydrocarbon tails
Are the two hydrocarbon tails hydrophobic or hydrophilic?
hydrophobic (scared of water)
Does the membrane core have low permeability or high permeability to all hydrophilic particles?
Low
low membrane permeability…
makes it possible to maintain differences in concentration (concentration gradients) across a membrane
Examples of hydrophilic particles
Ions with positive or negative charge, polar molecules, glucose
Examples of low permeability:
large molecules: proteins, starch, glycogen, cellulose
polar molecules: glucose, amino acids
ions: chloride, sodium, potassium, phosphate
Solutes near membrane…
might penetrate between the hydrophilic phosphate heads of the phospholipids
Larger the molecule…
lower the permeability
Simple Diffusion
- smaller, nonpolar (hydrophobic) molecules
- concentration gradient is high to low
- ATP is NOT required
Example of simple diffusion
if oxygen concentration inside a cell is reduced from aerobic respiration, oxygen will pass through membrane by passive (simple) diffusion
Polar molecules & simple diffusion?
Can diffuse at low rates
Two groups of membrane proteins
Integral proteins & peripheral proteins
Integral proteins
- hydrophobic on part of their surface and embedded in hydrocarbon chains in center of membrane
- may fit in both or one of phospholipid layers
- some are transmembrane proteins
Transmembrane (subset of integral) proteins
they extend across the membrane with hydrophilic parts projecting through the regions of phosphate heads on either side
Peripheral proteins
- Hydrophilic on surface, not embedded in membrane
- attached to surface of integral proteins
- some have a single hydrocarbon chain attached to them, to anchor protein to membrane surface
the more active a membrane…
the higher its protein content (ie in membranes of chloroplasts and mitochondria, active in photosynthesis and respiration
Osmosis
Due to differences in the concentration of substances dissolved in water
How do substances dissolve?
By forming intermolecular bonds with water molecules (to restrict movement of water molecules)
Higher solute concentration…
lower concentration of water molecules that are free to move
net movement of water
lower solute concentration to higher solute concentration
Aquaporins (transport protein)
Increase membrane permeability to water (ie kidney cells that reabsorb water, root hair cells that absorb water from soil)
Channel protein
Integral transmembrane protein with a pore that connects the cytoplasm to the aqueous solution outside the cell (net movement high to low)
Facilitated diffusion
one in which channel proteins are required (passive, no energy)
Pump proteins (active transport)
- use energy so they carry out active transport
- only move particles across membrane in one direction
- move against concentration gradient (low to high)
- ATP is used
Semi permeable membrane
allows passage of certain small solutes and is freely permeable to the solvent (ie facilitated diffusion and active transport) (nonexamples: channel and pump proteins, specific to particular particles, simple diffusion: not selective only depends on size and polarity of particles)
controlling movement of molecules:
change KE –> manipulate temp –> change concentration gradient –> manipulate concentration –> change SA/V ratio –> manipulate surface area
Glycoproteins
conjugated proteins w carbohydrates as non-polypeptide component & component of plasma membrane of cells, protein part embedded in membrane and carb part projecting out into the exterior environment of cell
Glycolipids
- molecules consisting of carbs linked to lipids
- carb is single monosaccharide or short chain of 2-4 sugar units
- lipid contains one or two hydrocarbon chains, which natrually fit into hydrophobic core of membranes
- occur in plasma membrane of all eukaryotic cells, w attached carb projecting outwards into the extracellular environment
- have a role in cell recognition
glycoproteins and glycolipids
form a carbohydrate rich layer on outer face of plasma membrane of animal cells, w an aqueous solution in gaps between carbs (called the glycocalyx)
vesicles
small sac of membrane w a droplet of fluid inside, can be used to move materials around cells
movement of vesicles
protein is synthesized by ribosomes on the rER and accumulates –> vesicles containing the proteins bud off the rER and carry to Golgi apparatus
Endocytosis
- small region of membrane is pulled and pinched off
- use ATP
- these vesicles contain water and solutes from outside cell
- often, they contain larger molecules needed by the cell that cannot pass across the plasma membrane
exocytosis
- vesicles fuse with a target membrane and disappear
- transfers all the contents of a vesicles across the membrane
- if a vesicles fuses w plasma membrane, contents are expelled from cell
- can also be used to expel waste products
example of exocytosis
polypeptides that have been processed in the Golgi apparatus are carried to the plasma membrane in vesicles for exocytosis
No membrane organelles
ribosomes, centrioles, microtubules, proteasomes, nucleoli
single membrane organelles
vesicles, vacuoles, rER, sER, golgi, lysosome
double membrane organelles
nuclei, mitochondria, chloroplast, amyloplast, chromoplast
Why aren’t cell walls organelles
Outside the plasma membrane, so extracellular structures rather than organelles
Why isn’t the cytoskeleton an organelle?
it consists of narrow protein filaments spread through much of the cell, not discrete enough
Why isn’t the cytoplasm n organelle?
not a discrete structure
Advantage of seperation of nucleus and cytoplasm into seperate compartments?
(Eukaryotes): Keeping chromsomes inside nucleus safeguards the DNA
Advantages of compartmentalization in cytoplasm of cells
- Enzymes and substrates can be much more concentrated
- Substances that can cause damage to cell can be kept inside membrane of organelle (ie digestive enzymes in lysosome)
- Conditions such as pH can be maintained at ideal level
- Organelles with their contents can be moved around
- Larger area of membrane availible for processes that happen within or across membranes
Fertilization
fusion of male and female gamete to produce a single cell
Zygote
an unspecialized cell produced from fertilization
Cell divides repeatedly to generate an embryo of many cells
zygote -> 2 cell stage -> 4 cell stage -> 16 cell stage -> morula -> blastocyst (inner cell mass make the animal, outer cells give rise to placenta) -> embryo
mitosis
ensures that cells in an embryo are all genetically identical
as embryo grows
cells become specialized for specific functions
differentation
development of cells in different ways to carry out specific functions aka the process by which cells in a multicellular organism become “different” from one another -> specialzied in structure and function
gene expression
when a certain gene is being used in a cell
advantage of differentation
division of labor due to cell specialization -> greater efficiency
multicellular organisms:
have the same genome
How cells differentiate into what?
- chemical signals from nearby cells
- physical contact w nearby cells
- chemicals inside the cytoplasm
- positional information
Gradients of signaling chemicals
indicate a cell’s position in the embryo and determine which pathway of differentiation it follows (ie gradients of retinoic acid guide differentiation of cells in the development of forelimbs, pancreas, lungs, kidneys)
properties of stem cells
- can divide repeatedly
- can remain or differentiate into specific cell type
precise location of stem cells within a tissue
stem cell niche
totipotent stem cells
early-stage embryos composed entirely of stem cells, can differentiate into any cell type
pluripotent stem cells
still capable of differentiating into a range of cell types, but not all
EMBRYONIC STEM CELLS ARE PLURIPOTENT
multipotent stem cells
adult body, can differentiate into several types of mature cell
stem cells:
- necessary for embryonic development
- necessary for repair of adult body - to replace damaged or lost somatic/body cells
- gaining more and more importance for therapeutic purposes
rate at which substances cross the plasma membrane
depends on its surface area
If ratio (SA/V) is too small:
- substances will not enter the cell as quickly as they are required and waste products will accumulate
- cells may overheat bc metabolism produces heat faster than it is lost
Type I pneumocyte in alveoli
- adapted for diffusion of O2 and CO2
- little need for mitochondria or other organelles and volume of cytoplasm is very small
- very thin, distance less, increases rate of gas exchange
type II pneumocytes in alveoli
- more numerous (90%), occupy only 5% of SA
- contain mitochondria, rER, Lysosome
- large amounts of phospholipids are synthesized in the cytoplasm and stored in lamellar bodies (vesicles containing many layers of phospholipids and some proteins)
- PRODUCE SURFACTANT
why is the alveolus lined by a film of moisture?
allows oxygen to dissolve and then diffuse to the blood in the alveolar capillaries
surfactant
layers of phospholipids and proteins, reduce surface tension so that the alveolus does not collapse on itself
why do phospholipids form bilayers in water?
shields the hydrophobic tails from the aqueous environment and exposes the hydrophilic heads to the extracellular fluid and cytoplasm
Compare the location and timing of initiation of transcription and translation between prokaryotic and eukaryotic cells.
Prokaryotic transcription and translation occur simultaneously in the cytoplasm, and regulation occurs at the transcriptional level. Eukaryotic gene expression is regulated during transcription and RNA processing, which take place in the nucleus, and during protein translation, which takes place in the cytoplasm.
Outline why post-transcriptional modification of RNA is not possible in prokaryotic cells.
Post-transcriptional modifications to DNA are usually unnecessary in prokaryotic organisms due to the lack of introns and exons. Prokaryotic DNA exists as a single continuous strand, so the mRNA transcribed from the DNA is already a complete transcription product, and does not need to be processed further.
Outline the benefit of compartmentalization of lysosomes and phagocytic vacuoles in cells.
Phagocytic vacuole is specialized to engulf foreign objects, and is then fused with lysosome which contains digestive enzymes to break down the waste. Compartmentalization makes sure the rest of the cell is protected from these potentially dangerous substances.
Describe the structure and function of the pores in the nuclear membrane
Structure: hole in the nuclear membrane
Function: creates selective passageway which transports big molecules and small, charged molecules between nucleus and cytoplasm
-proteins move into the nucleus
-ribosomes move out of the nucleus
-different types of RNA for protein synthesis move out
alveolar epithelum
represents a physical barrier that protects from environmental insults by segregating inhaled foreign agents and regulating water and ions transport, thereby contributing to the maintenance of alveolar surface fluid balance.
List two examples of cells that are specialized for exchange of materials and have adaptations to increase the SA:V ratio.
- Intestinal tissue of the digestive tract may form a ruffled structure (villi) to increase the surface area of the inner lining.
- Alveoli within the lungs have membranous extensions called microvilli, which function to increase the total membrane surface.
List three adaptations of cells that maximize the SA: volume ratio.
- Long extensions, such as in neurons.
- Thin, flattened shape, such as in red blood cells.
- Microvilli, such as in small intestine epithelial cells.
Describe how the structure of the alveoli increases surface area for gas exchange.
They are surrounded by a rich capillary network to increase the capacity for gas exchange with the blood. They are roughly spherical in shape, in order to maximise the available surface area for gas exchange.
cholesterol in membrane
regulates fluidity -> less fluid at higher temps, more fluid at lower temps
