Studied by 21 people
what were the conditions on early earth?
lack of free oxygen: therefore, lack of ozone layer
higher concentrations of CO2 and methane: therefore, higher temperatures and ultraviolet light penetration
what did the conditions on early earth cause?
a variety of carbon compounds to form spontaneously by chemical processes that do not now occur
how do you know if something is living?
it have characteristics of MRS H GREN (movement, respiration, sensitivity, homeostasis, growth, reproduction, excretion, nutrition)
why are viruses considered to be non-living?
they lack a cell structure and organelles; therefore, are unable to perform most of the characteristics of life
they are unable to replicate independently; they need a host cell which they infect
what were necessary requirements for the evolution of the first cell?
self-assembly of simple organic compounds into polymers
some polymers need the ability to self replicate
membranes need to surround polymer to create a compartment that differs in chemistry from the exterior: compartmentalization
presence of a catalyst: catalysis
how are cells currently formed?
division of pre-existing cells
what was the Miller-Urey experiment?
recreated the conditions on Earth prior to life using a specific piece of apparatus - found that organic molecules could have been synthesized on Earth’s pre-biotic conditions
evaluation of Miller-Urey experiment
thought then vs now
methane availability:
then - atmosphere had high levels of methane
now - low levels of methane
the energy source:
then - electrical discharge as source of energy
now - nuclear, UV radiation and electrical discharge
nucleotides:
then - unable to generate nucleotides
now - nucleotides have been chemically synthesized a different way
compartmentalization
when a membrane encloses a space where the internal genetic material and biochemical processes differ from external
spontaneous formation of vesicles
it is possible that the coalescence of fatty acids formed spherical bilayers that surrounded the first cell
most likely the first cell’s membrane were made of fatty acids because of its amphipathic nature
forms a bilayer which spontaneously forms small vesicles, which could have formed the membranes of early cells
for early life to evolve, the following had to emerge:
a system capable of replicating itself
an ability to catalyse chemical reactions
why is RNA hypothesized to be the first genetic material?
because RNA can store genetic information and has enzymatic properties
it can self replicate
can assemble spontaneously from nucleotides
control the rate of chemical reactions: modern cells have ribozyme (RNA molecule that can act as an enzyme) that catalyses the formation of peptide bonds
evidence for last universal common ancestor
all living organisms:
shared genes
same genetic code
what is a possible theory related to LUCA
that other organisms formed around the same time as LUCA but became extinct due to competition for resources
what to remember about the timescale of life on Earth?
life has been evolving for immense lengths of time
where was evidence of evolution of LUCA found (+explain)
in hydrothermal vents on the ocean floor
scientists found fossilized structures in deep sea hydrothermal vents: fossilized evidence
analysis of sequence data from modern species that live near hydrothermal vents shows that they all share a common ancestor: genomic analysis
what does the cell theory state?
all living organisms are made up of one or more cells
cells are the basic functional unit of living organisms
new cells are produced from pre-existing cells
what is deductive reasoning?
an approach where one progresses from general ideas to specific conclusions
formula for magnification
magnification - image size / actual size of image
unit conversions
m (x1000) mm (x1000) micrometer (x1000) nm
electron microscopy (+ads)
use electrons to form an image
high magnification and resolution
3D images can be produced
freeze fracture (+ads)
a sample is rapidly frozen using liquid nitrogen and then broken apart in a vacuum
used to show internal organisation of membranes
cryogenic electron microscopy
flash freezing solutions containing proteins and exposing it to electrons to produce images of individual molecules
fluorescent stains in optical microscopy
stains are added to specific cell structures and organelles which when exposed to UV rays gives a detailed view of the specimen
immunofluorescence in optical microscopy
antibodies in stains which bind with target molecules and allows the detection of molecules like virus proteins
structure of common cells
DNA as genetic material: to be stored or transferred
cytoplasm: where many important reactions take place
a plasma membrane: is a bilayer and controls interactions between cell’s interior & exterior
prokaryotic cell structure
70S ribosomes: binds and reads mRNA in translation for production of proteins
naked DNA in a loop: no nucleus
cytoplasm: site of cellular reactions
plasma membrane: control substances from entering and exiting the cell
cell wall: for protection and maintaining shape
Gram-positive bacteria (+examples)
when a group of bacteria is able to retain a dye called crystal violet and appear blue/violet after exposure to dye
Bacillus and Staphylococcus
eukaryotic cell structure
plasma membrane
cytoplasm with 80S ribosomes
nucleus with DNA in histones contain in a double membrane with pores
membrane bound cytoplasmic organelles: mitochondria, endoplasmic reticulum, Golgi apparatus; vesicles or vacuoles (lysosomes)
cytoskeleton of microtubules and microfilaments
homeostasis, metabolism, nutrition, movement, excretion, growth, response to stimuli and reproduction
homeostasis: ability to regulate internal conditions
metabolism: all enzyme catalysed reactions in a cell
nutrition: acquisition of energy from absorbing organic matter or synthesizing organic molecules
movement: state of changing position
excretion: release of waste
growth: permanent increase in size
response to stimuli: ability to respond to a change in their environment
reproduction: ability to produce offspring
differences between animal, plant and fungi cells
presence of cell walls: plant, fungi
differences in size and function of vacuoles: animal (small), plant (large), fungi (small)
presence of chloroplasts and other plastids: plant
presence of centrioles: animals
presence of cilia and flagella: sometimes animals, fungi
atypical cell structure: striated muscle fibre
cells are multinucleate: multiple cells fused together
challenges the concept that cells work independently of each other
atypical cell structure: red blood cells
anucleate
atypical cell structure: aseptate fungal hyphae
multinucleate
atypical cell structure: phloem sieve tube
no end cell wall
lack many cell organelles: nucleus, ribosomes, mitochondria
endosymbiosis; endocytosis
when on organism lives within another organism
; when an organism is engulfed by another
origin of eukaryotes by endosymbiosis (+which organelles)
evidence suggests that eukaryotes evolved from a common unicellular ancestor that had a nucleus and reproduced sexually
: mitochondria and chloroplasts evolved from endosymbiosis
70S ribosomes, ability to replicate, naked circular DNA
what causes cell differentiation?
specialization of cells causing different shape and containing different organelles
gene expression (which gene is switched on) triggered by changes in the environment
what is multicellularity in cells? (+ads)
when cells of the same type group together to form tissues and carry out a specific function: has happened MANY TIMES
allows for organism to grow larger in size
cell specialization can occur
which few structural features are shared by all viruses?
small, fixed size
nucleic acid (DNA or RNA) as genetic material
a capsid made of protein
no cytoplasm
few or no enzymes
how do viruses differ from each other?
diverse in shape and structure
genetic material as DNA or RNA but single or double stranded
some are enveloped in host membrane, some not
examples of viruses
bacteriophage lambda: attaches to host cell and injects DNA in: double stranded DNA, protein capsid
HIV: two single-stranded RNA strands, viral envelop, protein capsid
coronavirus: single stranded RNA, spherical, enveloped
the lytic cycle
virus attaches, injects, controls machinery, releases new viral particles
the lysogenic cycle
virus attaches, injects, integrates with host DNA, reproduces and divides, environmental change triggers lytic cycle
convergent evolution and how viruses show evidence of it (+example)
organisms of that do not share a common ancestor share similar characteristics due to their similar environments e.g parasitism as a mode of existence
reasons for rapid evolution in viruses (+examples)
influenza & HIV
high mutation rates, large population sizes, short generation times
consequences for treating diseases caused by rapidly evolving viruses
vaccines need to be changed and updated
isolation of infected individuals
what shape do phospholipids and other amphipathic lipids form in water?
continuous sheet like bilayers: hydrophilic head and hydrophobic tail
what can or cannot pass through the hydrophobic core of a bilayer?
low permeability to large molecules, ions and polar molecules (hydrophilic)
simple diffusion across membranes (+examples)
particles moving from areas of high concentration to areas of low concentration
e.g in respiration oxygen diffuses into the cell from high to low, and carbon dioxide diffuses out of the cell from high to low
difference between integral and peripheral proteins
integral: hydrophobic (amphipathic), embedded in bilayer across both layers or one layer
peripheral: hydrophilic, attached to integral protein of plasma membrane, can be inside or outside cell
define osmosis
the diffusion of water molecules across a concentration gradient from area of high concentration to areas of low concentration
difference between dilute solution and concentrated solution
dilute - high concentration of water
concentrated - low concentration of water
what is meant by random movement of particles?
movement caused by the kinetic energy of the molecules or ions
define impermeability of membranes
to what extent the membrane allows particles to pass through
facilitated diffusion
the particles that cannot pass through the bilayer (large molecules, ions, polar molecules) need the help of transport proteins (channel, carrier proteins)
passive form of transport: does not require energy
channel proteins and how is it selectively permeable?
pores that allow the passage of charged molecules (e.g ions) across a membrane
they can be gated: they open and close for particles to pass
carrier proteins
changes shape when binding occurs
molecules binds at binding site and protein changes shape causing the other side to open for allow passage
define active transport (+explain)
the movement of molecules across a membrane from areas of low concentration to high concentration using energy from respiration (hydrolysed ATP)
across a concentration gradient
carrier proteins as pumps and use energy from ATP to pump particles across concentration gradient
why are facilitated diffusion and active transport selectively permeable, but simple diffusion is not?
facilitated diffusion and active transport only operate when specific molecules interact with the proteins, however simple diffusion is not selective and depends only on the size and hydrophilic/phobic properties of particles
what are glycoproteins and glycolipids?
glycoproteins: cell membrane proteins that have a carbohydrate chain attached on the extracellular side
glycolipids: cell membrane lipids that have a carbohydrate chain attached on the extracellular side
what are the roles of glycoproteins and glycolipids in cell adhesion and cell recognition?
cell adhesion: the carbohydrate chain acts as a receptor molecule and binds to substances at the cell surface
cell recognition: the molecules can act as markers for cell identification
how does the fatty acid composition of the bilayer affect the fluidity
unsaturated fatty acids contain one or more double bonds meaning it is bent and not tightly packed: therefore, the melting point is low.
this allows the bilayer to be flexible & fluid at higher temperatures
saturated fatty acids have no double bonds meaning they are tightly packed and straight: therefore, the melting point is high.
this means the bilayer is stable and strong. at higher temperatures
cholesterol in membranes (characteristics & roles)
it is amphipathic and is located in the bilayer; is an important membrane lipid
it acts as a modulator of fluidity and permeability of membranes:
at low temperatures, it disrupts the close packing of the phospholipids to allow flexibility
at high temperatures, it holds fatty acid tail together for stability
endocytosis (+example)
transports materials into cells
plasma membrane engulfs material creating a small sac around it
e.g engulfing of bacteria by phagocytic white blood cells
exocytosis (+example)
transport materials out of the cell
substances packaged into a secretory vesicle which fuses with the membrane and releases its contents
e.g secretion of digestive enzymes from pancreatic cells
what are gated ion channels? (+examples)
channels in some membranes which operate in response to chemical or electrical stimuli
neurotransmitter-gated ion channels, voltage-gated ion channels
neurotransmitter-gated ion channels (+example)
the neurotransmitter acetylcholine can bind to nicotinic acetylcholine receptors triggers the ion channel to open
voltage-gated ion channels (+example, steps)
sodium-potassium pumps are integral proteins that are exchange transporters
three sodium molecules out and two potassium molecules in using one ATP
moves ions against concentration gradient via active transport
1) three sodium binds and phosphorylation changes the shape of the protein to open
2) two potassium bind and phosphate detaches to change shape to open the other side
importance of sodium-potassium pumps in generating membrane potential
more positive sodium out than positive potassium in: meaning the external is more positive than the internal
what is indirect active transport?
uses the energy released when one molecules move down a concentration gradient to move another against the concentration gradient
what is cotransport?
the coupled movement of substances across a membrane through a carrier protein and occur at the same time
explain sodium-dependent glucose co-transport (+example)
sodium goes from low to high conc. first which requires ATP, but then glucose is coupled with sodium as it goes back from high to low (passive: doesn’t require energy) => is supposed to require energy to pump glucose from low to high but doesn’t because it goes through co-transporter with sodium
cell adhesion molecules (CAMs) & are they all the same?
required to carry out cell adhesion by binding cells with other cells or the extracellular matrix
different CAMs are used for different cell-cell junctions
what are and are not considered organelles and why?
are:
nucleus, ribosomes, vesicles, plasma membrane
not:
cell wall, cytoskeleton, cytoplasm
because they don’t have a membrane
advantage to having a seperate nucleus and cytoplasm
eukaryotes:
gene transcription occur in the nucleus and post-transcriptional modification can take place before going to ribosomes for gene translation
prokaryotes:
gene transcription and translation take place simultaneously because of the lack of nucleus, and mRNA immediately meets the ribosomes after transcription
advantage of compartmentalization of cells in the cytoplasm (+examples)
allows for the seperation of incompatible biochemical processes: pathways needing metabolites and enzymes run smoothly without risk of interferences from other structures
e.g lysosomes require lytic enzymes which could be harmful if not surrounded by a membrane
e.g phagocytic vacuoles during exocytosis ensures harmful substances like bacteria are not in contact with the rest of the cell
adaptations of the mitochondria for ATP production by aerobic cell respiration
double membrane with small volume of intermembrane space: for concentration build up of hydrogen ions
large surface area of cristae: to hold many proteins and enzymes
compartmentalization of enzymes of the Krebs Cycle in the matrix: so respiration reaction can happen more efficiently
adaptation of chloroplasts for photosynthesis
small volumes of fluid inside thylakoids: so a proton gradient can develop quickly
large surface area of thylakoid membranes with photosystems: maximum absorption of light
compartmentalization of enzymes of the Calvin Cycle in the stroma: so respiration reaction can happen more efficiently
functional benefits of the double membrane of the nucleus
need for pores in the nuclear membrane: to mRNA and ribosomes out, and enzymes in
for the nucleus membrane to break into vesicles during mitosis and meiosis: for cellular division
difference in structure and function of free ribosomes and rough endoplasmic reticulum bound ribosomes
free ribosomes synthesize proteins for inside the cell
bound ribosomes synthesize proteins for transport within the cell and secretion
structure and function of the Golgi apparatus
flattened sacs of membrane called cisternae
processes protein into Golgi vesicles before being transported to needed destination; usually secretion
role of clathrin in the formation of vesicles
lines the vesicle, with the help of the cytoskeleton forms a well after the target molecule is bound
describe a stem cell
a cell able to divide an unlimited amount of time by mitosis, each new cell can either stay a stem cell or become a specialized cell by differentiation along different pathways
stem cell niches (+examples and function)
the specific location in the human body where stem cells remain: maintains inactive cells and stimulates proliferation and differentiation
e.g bone marrow as a stem cell niche for red blood cells, white blood cells and platelets
e.g hair follicle as a stem cell niche to promote hair growth
difference between totipotent, pluripotent and multipotent stem cells (+example)
toti: stem cells that can differentiate into any cell type found in the embryo and extra-embryonic cells (whole organism)
pluri: embryonic stem cells can differentiate into any type of cell type found in the embryo but not extra-embryonic cells (all body cells)
multi: adult stem cells that can differentiate into closely related cell types
e.g embryonic stem cells are first totipotent and then change to pluripotent
define potency
ability of stem cells to differentiate into specialized stem cell types
cell size of sperm, egg, RBC, WBC, neurons, striated muscle fibre
sperm: 55 micrometer
egg: 100 micrometer
RBC: 8 micrometer
WBC: 12-17 micrometer
neuron: 300-400 micrometer
striated muscle fibre: 300 millimeter
surface area to volume ratio and constraints on cell size
surface area doesn’t increase at the same rate as volume: as cell size increases the SA:V ratio decreases as there is less surface area in relation to volume
as volume increases, the cell’s metabolic requirements increases, however it ability to exchange does not increase at the same rate
adaptations to increase SA:V ratio in cells
RBC is flattened and biconcave
proximal convoluted tubule cells have microvilli and invagination
adaptations of type I and type II pneumocytes in alveoli (+example with both types)
type I: extremely thin alveolar cells for short diffusion distance
type II: presence of secretory vesicles that bring surfactant to alveolar lumen
e.g alveolar epithelium is a tissue with more than one cell type because different adaptations are required for the overall function
adaptation of striated muscle fibres and cardiac muscle cells
contractile myofibrils
adaptations of human gametes
sperm: flagellum, many mitochondria, haploid nucleus
egg: haploid nucleus, cytoplasm rich in nutrients, large in size
why is water a good solvent?
because it is dipolar: hydrogen side is slightly positive, oxygen side is slightly negative
allows water molecules to form hydrogen bonds with other polar solutes and ions
difference between hypertonic, hypotonic and isotonic solutions
hypertonic: solute concentration is more outside the cell, water goes out of the cell
hypotonic: solute concentration is less outside the cell, water goes into the cell
isotonic: solute concentration is the same on both sides (dynamic equilibrium) = no net movement
effects of water movement on cells that lack a cell wall (+example of adaptations for unicellular and multicellular organisms)
hypotonic medium: swelling and bursting
hypertonic medium: shrinkage and crenation
e.g need for contractile vacuoles in freshwater unicellular organisms to remove water
e.g need to maintain isotonic fluid in multicellular organisms to prevent harmful changes
effects of water movement on cells with a cell wall
hypotonic: turgor pressure (protoplasts expands onto cell wall)
hypertonic: plasmolysis (protoplasts pulls away from cell wall
medical applications of isotonic solutions
intravenous fluids and bathing of organs ready for transplantation
define water potential (explain absolute and conditions)
the potential energy of water, per unit volume, relative to pure water: the tendency of water molecules to move from low to high concentration areas
the absolute quantity potential energy of water cannot be found
20 degrees, atmospheric pressure, kPa
movement of water related to potential energy
water molecules move from areas of high water potential to areas of low water potentials, but areas of low solute to areas of high solute
