intro - basic cell biology Flashcards
1
Q
what is the role of the plasma membrane
A
- defines/marks the boundary of all cells
- constructed of a selectively permeable phospholipid bilayer
2
Q
what does selectively permeable mean
A
- only lets pass certain chemical compounds
- impermeable barrier to others
3
Q
what does establishing this boundary to the outside of the cell + defining a boundary to the inside do
A
regulates the internal cellular composition
4
Q
what type of environments do cells carry out biochemical reactions in
A
sometimes very cultic
5
Q
what are lipid micelles
A
- made of bilayer of phospholipids that spontanteously organises as a barrier function
- enclosed space w/in an aqueous environment
6
Q
how do cells generate order in chaotic environments
A
- entropy and enthalpy
- constantly use energy to create ordered structures + generate energy
7
Q
what happens when cells generate energy
A
- dissipated as heat to the environment
- increases disorder on the outside + order of matter on inside
- only possible due to membrane separating these 2 regions of different entropies
8
Q
what makes up metabolism and what is it
A
catabolism and anabolism
- building structures /components needed to carry out living functions
9
Q
why is the barrier function so critical
A
defines a distinct environment in which the cell can
1) use chemicals to produce energy
2) metabolise
3) excrete waste product
10
Q
how do amphiphilic phospholipids orient themselves in membrane
A
- tail (hydrophobic - doesnt mix w h2o, turns away from it ie fat droplets) = towards hydrophobic / non-water containing liquid phases
- head (hydrophilic - miscible w h2o) = towards water
11
Q
so what is formed when phospholipids are put into a bilayer construct
A
structure in an aqueous environment which in itself encloses an aqueous environment
12
Q
what is the intracellular environment made of
A
water containing space
13
Q
what is the problem of monolayers
A
only have
1 aqueous phase
and 1 phase made up of oil or fat unsuitable as an intracellular cytoplasmic space
14
Q
how are phospholipids miscible with water
A
because have a charged part of the molecule (head group)
15
Q
what else is contained in cellular membranes
A
proteins which are suspended in the bilayer
ie transport channels for solutes
16
Q
what is the basic structure of a phospholipid
A
- nonpolar, uncharged, hydrophobic, fatty acid, hydrocarbon tail linked through a cholesterol group + a phosphate to the head groups
- hydrophilic head groups = charged, define differences of different phospholipids
17
Q
which molecules can freely pass across by simple diffusion and what are their properties
A
- O2, CO2, N2, steroid hormones
- hydrophobic non charged (small uncharged) as can go through the hydrophobic phase
18
Q
which molecules can partially pass across by diffusion even if polar and what are their properties
A
H2O, urea, glycerol, NH3
- if don’t have a strong charge attached to them
- small uncharged polar
19
Q
which molecules cant pass across plasma membrane by diffusion and what do they need
A
- large uncharged molecules (glucose, sucrose)
- need form of active transport that mediates exchange between extra + intracellular space separated by the lipid membrane barrier
20
Q
which molecules cannot pass the hydrophobic part of lipid bilayer membrane
A
- ions
- miscible w water on both sides BUT cannot pass hydrophobic lipid phase bc of their charge
21
Q
how do protein transporters mediate transport across the plasma membrane
A
- opened
- binds to solute (ie glucose)
- changes its conformation / 3D structure whilst its binding to mediate the transport of it to the intracellular space
22
Q
how do channel proteins mediate transport across the plasma membrane
A
- either always open
- or open under specific conditions to let solutes pass freely through a channel or pore so they can mediate high freq transport across plasma membrane
- important in nerve signalling + nerve cells
23
Q
passive transport is
A
- transport mediated by proteins that form channels or doors
- follows conc gradient so uses energy provided by principle of diffusion to enter the cell
24
Q
how are molecules moved against the concentration gradient
A
- certain membrane proteins expedite energy to do so (ie that bound in ATP)
25
what are the 2 basic forms cells are assigned to
- eukaryotic (us, cells of higher life, highly organised, contain membrane enclosed intracellular organelles, nucleus)
- prokaryotic (genetic info freely suspended in cytoplasm, mostly have cell wall to resist hydrodynamic pressures of osmotic pressure in aqeous environments, simple, usually unicellular organisms, NO membrane enclosed intracellular organelles)
26
what does prokaryote mean
without a nucleus
27
describe the structure of prokaryotes
- contain basic form of plasma membrane
- genetic info (DNA) suspended in cytoplasm
- ribosomes translate mRNA to proteins
- cell wall
- flagellum (motility)
28
what is the major difference of pro to eukaryotic
pro = generally do not contain organised membranous internal structures
29
what is the purpose of prokaryotic cell wall
- protects cell from the pressure arising from water diffusing in
- prevents cell from rupturing bc of diffusion + osmosis to keep their integrity in hypotonic environment
30
what shapes do prokaryotes come in
spherical shaped, rod shaped, spiral
- spirillum
- spirochete
- coccus
- coccobacillus
- vibrio
- bacillus
31
what can occur in a prokaryotic cell but NEVER in eukaryotic (due to nucleus)
transcription + translation of genetic info can occur simultaneously
32
what are protists
algae, fungi, protozoa like amoeba
| - unicellular organisms similar to bacteria but based on eukaryotic cells
33
eukaryotic cells include
all plant and animal cells as multicellular organisms
34
how do single celled amoeba move
use actin polymerisation to push out pseudopods (false feet)
35
give an example of the diverse morphology range of eukaryotic cells
- large neuronal nerve cell to tiny neutrophil cells (of the immune system)
- diverse cells
- highly specialised functions esp in muticellular organisms
36
how have we formed phylogenic evolutionary trees and what do they show
- by sequencing ribosomal rna genes + comparing them
shows
1) common ancestor cell at the beginning of life
2) prokaryotic life evolved into bacteria
3) prokaryotic evolved further into archaea (formerly called archaea bacteria BUT this isn’t accurate)
4) archaea into eukaryotes
37
what first prokaryotic life still exists today
bacteria ie pathogens, e-coli
38
what are archaea
- prokaryotes (different from bacterial prokaryotes)
- precursors to eukaryotic life
- they were establishing intracellular membrane enclosed organelles so became eukaryotic (start of complex life on earth)
39
what evolved from single celled eukaryotes
more complex multicellular organisms of animals + plants evolved
40
what can single celled eukaryotes be, give an example (eukaryotes = complex, many different organisations and forms of life)
- protists (ie amoeba)
- chlorella microalgae (can perform photosynthesis)
- other unicellular motile or immotile prokaryotic cells that live in aqueous environments on their own
41
```
give a
a) dental example
b) plant example
c) body example
of many specialised eukaryotic cells
```
a) in a tooth bud
- odontoblasts
- ameloblasts
- enamel
- dentine
b) fearn leaf cells perform photosynthesis in form of multicellular organisms
c) shapes that follow their function = skeletal muscles fibres, nerve fibres, heart muscle cells, lymphocytes
42
which membrane enclosed structures are in the intracellular organisation of eukaryotes
- endoplasmic reticulum = main sites of protein synthesis
- nucleus = contains genetic info of the cell
- mitochondia = prepare energy for the cell (ie oxidative phophorylation)
- golgi system = proteins packaged for secretion into vesicles that are released by the cell into the extracellular space
43
which filamentous protein structures are part of the cytoskeleton of eukaryotic cells
- microtubules (help cells retain structures, resist stress + involved in cellular lockean motions = gives cells a means of motility)
44
what is the endosymbiosis theory
theories on how eukaryotic cells evolved from archaea cells and HOW they gained intracellular membrane bound organelles
- backed up by lots of experimental + evolutionary data
- widely accepted in scientific domain
- 2 models
45
explain the theory model demonstrating how precursor cells to eukaryotic cells have acquired mitochondrial organelles as sites of energy productions (acquisition of mitochondria organelles)
1) archaeal precursor cell engulfed + acquired an aerobic bacterium (prokaryotic cell)
2) ingested the cell
3) integrated these prokaryotic cells into its cellular machinery
4) form early aerobic eukaryotic cell precursor
46
how is the model for the acquisition of mitochondria organelles supported
- certain aspects of membrane structure of mitochondria = v similar to prokaryotes
ie
1) contain a little bit of a genome v similar to prokaryotic genomes
so
archaeal precursor ingested prokaryotic cells + cannibalise for cellular functions of energy production
47
what is the 2nd theory model demonstrating how chloroplast organelles were acquired by precursor cells to eukaryotic cells
same theory but for plant cells
1) archaeal precursor cell additionally ingested a PHOTOSYNTHETIC BACTERIUM as a precursor for chloroplast
2) establish chloroplast as membrane encircled intracellular organelle for photosynthetic function in eukaryotic cell
48
what is the purpose of the cytoskeleton of eukaryotic cells
- structural integrity
- allows locomotion (contract + move ie in muscle fibres)
- mediates intracellular transport via microtubular cytoskeletal components (protein loaded organelles / vesicles moved around the cell on these)
49
what is the function of the spindle apparatus
- separates chromosomes during mitotic or meitotic cellular division
- mediates chromosomal division
50
what responses of cells to external stimuli is the cytoskeleton implicated in
1) mechanosensing
- sensing + response to external mechanical forces
- sensing of extracellular substrate stiffness
- cells can sense stiffness of substrates theyre attaching to / sitting on + can carry out certain functions or differentiate into certain cell types
51
how is mechanosensing important in regenerative medicine
biomaterials worked on as biocompatible systems for tissue regeneration usually try to emulate stiffness similar to the target tissue we want to obtain bc cells respond to surface stiffness (through the cytoskeleton)
52
what structural proteins does the cytoskeleton consist of
- actin filaments (7nm diameter)
- intermediate filaments (10nm)
- tubulin filaments (25nm)
53
explain the role of actin filament in the cytoskeleton cells
- dispersed throughout
- high abundance in areas of cellular or mechanical stress
- stress fibres = mediate structural integrity to cell
- mediate locomotion or contraction
54
how is muscle contraction mediated in system of muscle fibres
by actin-myosin discs of muscle fibres
55
explain the role of intermediate filament in the cytoskeleton cells
- Many different subtypes
1) lamins (mediate integrity of nucleus)
2) keratins (mediate structural integrity to cell)
56
explain the role of tubulin filament in the cytoskeleton cells
- made of α- and β-tubulins sub units = polymerize to microtubules (act as rails to transport organelles to difference locations in the cell)
- assembly of + part of mitotic spindle
57
why cant transcription and translation happen at same time in eukaryotes
- genetic info contained in membrane enclosed nucleus
- mRNA synthesised in nucleus then exported ACTIVELY to cytoplasm
- proteins synthesised in the cytosol (at ribosomes)
- transcription has to be completed + mrna exported BEFORE translation to a protein can begin
58
what is the differnce between cell cycles of pro and eukaryotes
```
pro = continous process
euk = discrete steps, highly regulated process (mitosis)
```
59
what happens if cell cycle in cellular division is disregulated or out of control in multicellular organisms
uncontrolled cell growth
| cancer
60
why is cell cycle so highly coordinated in eukaryote cells
- normal functions on hold whilst the cells divide
| - DNA synthesis needs to be completed before cell division can occur
61
what are the 4 phases of eukaryotic cell division
1) G1
- cell carries out its standard functions
2) S (synthesis) PHASE
- cell gets signal that permits it to replicate
- genetic info duplicated
3) G2
- checkpoints where integrity of the genetic info - completion of steps of S phase are checked
4) M (mitosis) PHASE
- nucleus divides are chromosomes segregated
- then cytokinesis
62
what phase can the cell exit to from the G1 phase in rare case
G0
| - cell undergoes senescence + doesn’t do much anymore
63
what are the 6 phases of mitosis
1) INTERPHASE
- genetic info in the cell is 2N (2 copies of the genome)
2) PROPHASE
- chromosomes condense + spiralise
- synthesis happens to 4N
3) METAPHASE
- chromosomes align with centromere on equator
- attach to mitotic spindle apparatus (made out of microtubules that attach to the chromosome)
4) ANAPHASE
- mediated division of genetic info in equal proportions towards opposite poles (spindle contracts to move the chromatids)
- preparation to form 2 daughter cells
5) TELOPHASE
- 2 nuclei reform at poles
6) CYTOKINESIS
- separation in 2 daughter cells with 2N genetic info (DIPloid)
64
what happens to chromosomes (2 chromatids) in mitosis
- ensure equal separation + distribution of genetic info to daughter cells
- only visible + occur during cellular division
- during anaphase and telophase = condensed and attached to spindle by centromere
- highly condensed, made up of proteins and nucleic acid
65
how is DNA condensed in chromosomes
- condensed into structures of higher levels of organisation
1) double helix wrapped around histone proteins (forms 'beads-on-a-string structure)
2) beads on a string wrapped into a chromatin fibre of packed nucleosomes
3) chromatin fibre folded into loops
4) loops form part of mitotic chromosome (2 chromatids attached at centromere)
66
what does the packing of dna enable
dna molecules to be condensed into mitotic chromosome at 10,000 fold shorter than would be at its extended length
SO
allows ordered separation + distribution of genetic info during mitosis
67
when does meiosis occur in eukaryotes
- for sexual reproduction (in gametes - makes egg and sperm cells)
68
why is meiosis different to mitosis
- products are HAPloid gametes (1N only)
- there are 2 divisions
- 2nd is a reduction division = leading to 4 genetically different haploid daughter cells from 1 adult cell
69
what happens in meisosis 1 to give rise to genetic variation
homologous recombination (mixing + shuffling of genetic into of parental cell)
70
what are introns
explain their
a) absence in prokaryotes
b) presence in eukaryotes
non coding areas of mRNA
a) genes not broken up into different portions by intron insertions
b) widespread presence, mrna spliced to remove them + lead to usable opened reading frame
71
how many types of RNA polymerase exist in
a) eukaryotes
b) prokaryotes
a) 3
| b) 1
72
what is the difference in the ribosome of
a) eukaryotes
b) prokaryotes
a) 80S type
- larger, more complex
b) 70S type
73
what type of translation is seen in
a) eukaryotes
b) prokaryotes
a) monocistronic
- every mRNA only encodes 1 reading frame for 1 gene for 1 protein product
b) polycistonic
- 1 mrna can have multiple reading frames for different genes in different protein products
- many diff proteins can be translated from 1 mRNA
74
what are viruses
- borderline of living entities and non living chemicals
- NOT living cells and cannot carry out any living functions on their own
- Obligate intracellular parasites (hijack other cell to replicate)
75
what is the main approach for classifying viruses
- look at their genome
1) dna genome (herpes, poxvirus, papillomavirus)
2) rna genome (covid, HIV, influenza)
76
what are viruses usually made up of
- capsid
| - envelope (encloses genetic info)
77
which viruses infect bacteria, give an example of a family of these viruses
- bacteriophage
| - T7 family
78
how is the human influenza virus complex
- many different proteins displayed on outside of the viral capsid (haemagglutinin + neuraminidase)
- these = targets for antiviral drugs
79
what is the process of viral infection + release by the endocytosis and fusion method
- trigger active uptake of viral particle by endocytosis
- taken up in an endosomal vesicle (intracellular, membrane enclosed)
- fuse with endosome
- release their genome into the cytoplasm
80
what is the process of viral infection + release by the fusion method
- direct fusion with plasma membrane
| - immediate release of genetic information into cytoplasm
81
what is the process of viral infection + release by the endocytosis and lysis method
- virus taken up by active mechanism
- enters an endosome
- doesn't escaping by fusing w it
- actively triggers lysis/rupture of the endosome
- so release of the viral genome into the cytoplasm
- cell dies in process
82
how are viral particles released into the environment to infect more cells following assembly by the cellular machinery
2 WAYS
1) virus lyses cells, they rupture releasing all viral particles, cell dies
2) continuously shed from cell by bubbling (lysogenic viruses do this - those not lytic), infected cell kept alive, viruses continuously released = ie HIV
83
what can happen if a protein is a specific type of rna virus
rna directly used as mRNA for protein translation + production of viral proteins
84
what is another method of converting a cell to a virus production cell
- pore formation
1) endocytosis
2) uncoating, pore formation
85
what does a virus need to do if it has a dna genome
1) dna to nucleus
| 2) transcribed into rna before formed into proteins
86
what are prions
- not living
- info that can replicate in living systems and cause disease
- proteins (NOT nucleic acid or genetic info)
87
how were prions identified
- mad cow disease
| - kuru in tribes practicing cannabolism
88
how did prions (KURU) cause disease in South Fore people of Papua New Guinea
- practice cannabalism
| - dementia / neurogenerative disease occuring bc of eating brains of people that have been affected by a prion disease
89
what happens in prion disease
1) prions are proteins that naturally occuring in brain in form of PrP^C (highly stable + cannot be degraded)
2) during the disease the proteins gain a different structure (irreversible conformational change) to PrP^SC
3) disease molecule can spontaneously occur OR be ingested into organism (ie eating beef of infected cow)
4) it confers its structure to healthy protein (all prion precursor proteins converted into diseased structure by prion proteins)
5) diseased structure can NOT be degraded in the body so causes disease
90
what does PrP^SC (diseased form of the protein) cause
- accumulates in the brain
| - causes irreversible neurodegenerative spongiform disease (brain lesions and protein accumulation)
91
what are prion diseases known as and why
transmissible spongiform encephalopathies
- post mortem appearance of the brain
1) large vacuoles (holes) in the cortex and cerebellum
2) leads to deterioration + destruction of brain function
92
what is surprising about prions
protein is infectious agent + can transmit an infectious disease
93
what are examples of TRANSMISSIBLE SPONGIFORM ENCEPHALOPATHIES (TSE) caused by prions
- scrapie = neurodegenerative, found in sheep flocks, persists in soil where sheep are held, can reinfect)
- BSE (bovine spongiform encephalopathy) = caused by feeding infected sheep to cattle
- new variant CJD (Creutzfeld Jakob Disease)
= human form of bse, by eating infected cattle
94
how can prions cause disease in clinical practice (very important) and how can we prevent this
- theyre V RESISTANT (to heat and UV irradiation) + do not degrade
- no sterilisation method can give 100% guarantee of inactivating them (autoclaving, incineration, irradiation, resistant to formaldehyde treatment)
- risk = irreversible contamination of surgical instruments
- prevent = use DISPOSABLE instruments
- still not prevalent in human pop but inc’ing growing risk
95
which prions are most to least resistant to UV
most = scrapie
gene
bacterium
least = bacteriophage
