unit 2 Flashcards
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Cell membrane
structure
Phospholipid bilayer with
embedded intrinsic & extrinsic
proteins
Cell membrane
function
Selectively permeable barrier
controls passage of substances
in and out the cell
barrier between internal and
external cell environments
Nucleus
Structure
Nuclear pores, nucleolus, DNA
and nuclear envelope
Nucleus
Function
site of transcription & premRNA splicing - mRNA
production
site of DNA replication
nucleolus makes ribosomes
nuclear pore allows movement
of substances to/from
cytoplasm
Mitochondria
Structure
Double membrane with inner
membrane folded into cristae
70S ribosomes in matrix
small, circular DNA
enzymes in matrix
Mitochondria
Function
site of aerobic respiration
produces ATP
Chloroplast
structure
Thylakoid membranes stacked
to form grana, linked by
lamellae
stroma contains enzymes
contains starch granules, small
circular DNA and 70S ribosomes
chloroplast
function
Chlorophyll absorbs light for
photosynthesis to produce
organic molecules (glucose)
Organisms
containing
chloroplasts
Plants
Algae
Golgi apparatus
stucture
Fluid-filled, membrane-bound
sacs (horseshoe shaped)
vesicles at edge
Golgi apparatus
function
Modifies proteins received from
RER
packages them into vesicles to
transport to cell membrane for
exocytosis
makes lysosomes
Lysosome
structure
type of Golgi vesicle containing
digestive enzymes
Lysosome
function
Contains digestive enzymes
e.g lysozymes to hydrolyse
pathogens/cell waste products
Rough
endoplasmic
reticulum function
Site of protein synthesis
folds polypeptides to secondary
& tertiary structures
packaging into vesicles to
transport to Golgi
Smooth
endoplasmic
reticulum function
Synthesises and processes
lipids
Cell wall
function
Provides structural strength,
rigidity and support to cell
helps resist osmotic pressures
Ribosome
structure
Small and large subunit
made of protein and rRNA
free floating in cytoplasm &
bound to RER
70S in prokaryotes,
mitochondria and chloroplasts
80S in eukaryotes
Ribosome
function
Site of translation in protein
synthesis
Rough
endoplasmic
reticulum structure
System of membranes with
bound ribosomes
continuous with nucleus
Smooth
endoplasmic
reticulum structure
System of membranes with no
bound ribosomes
Cell wall
structure
In plant, fungal and bacterial
cells
plants - made of microfibrils of
cellulose
fungi - made of chitin
bacteria - murein
Cell vacuole
structure
Fluid-filled
surrounded by a single
membrane called a tonoplast
Occasional
features of
prokaryotes
Plasmids - loops of DNA
capsule surrounding cell wall -
helps agglutination + adds
protection
flagella for movement
Contrast
prokaryotic &
eukaryotic cells
prokaryotic cells are smaller
prokaryotes have no membrane
bound organelles
prokaryotes have smaller 70S
ribosomes
prokaryotes have no nucleus -
circular DNA not associated with
histones
prokaryotic cell wall made of
murein instead of
cellulose/chitin
Cell vacuole
function
Makes cells turgid - structural
support
temporary store of sugars,
amino acids
coloured pigments attract
pollinators
Protein
carriers
Bind with a molecule, e.g.
glucose, which causes a change
in the shape of the protein
this change in shape enables
the molecule to be released to
the other side of the membrane
Protein
channels
Tubes filled with water enabling
water-soluble ions to pass
through the membrane
selective
channel proteins only open in
the presence of certain ions
when they bind to the protein
Features of
viruses
Non living and acellular
contain genetic material, capsid
and attachment proteins
some (HIV) contain a lipid
envelope + enzymes (reverse
transcriptase)
3 types of
microscopes
Optical (light) microscopes
Scanning electron microscopes
(SEM)
Transmission electron
microscopes (TEM)
Magnification
How many times larger the
image is compared to the object
calculated by equation:
m=i/a
Resolution
The minimum distance between
two objects in which they can
still be viewed as separate
determined by wavelength of
light (for optical microscopes)
or electrons (for electron
microcopes)
Optical
microscopes
Beam of light used to create
image
glass lens used for focusing
2D coloured image produced
Evaluate
optical
microscopes
Poorer resolution as long
wavelength of light - small
organelles not visible
lower magnification
can view living samples
simple staining method
vaccum not required
Transmission
electron
microscopes
Beam of electrons passes
through the sample used to
create an image
focused using electromagnets
2D, black & white image
produced
can see internal ultrastructure
of cell
structures absorb electrons and
appear dark
Evaluation
TEMs
Highest resolving power
high magnification
extremely thin specimens
required
complex staining method
specimen must be dead
vaccum required
Scanning
electron
microscopes
Beam of electrons pass across
sample used to create image
focused using electromagnets
3D, black and white image
produced
electrons scattered across
specimen producing image
Why calibrate
eyepiece
graticule?
Calibration of the eyepiece is
required each time the objective
lens is changed
calibrate to work out the
distance between each division
at that magnification
Evaluation
SEMs
high resolving power
high magnification
thick specimens usable
complex staining method
specimen must be dead
vaccum required
Purpose of cell
fractionation
Break open cells & remove cell
debris
so organelles can be studied
Homogenisation
Process by which cells are
broken open so organelles are
free to be separated
done using homogeniser
(blender)
Homogenisation
conditions
Cold reduces enzyme activity
preventing organelle digestion
Isotonic prevents movement of
water by osmosis - no bursting /
shrivelling of organelles
Buffered resists pH changes
preventing organelle + enzyme
damage
Ultracentrifugation
Homogenate solution filtered to
remove cell debris
solution placed in a centrifuge
which spins at a low speed
initially
then increasingly faster speeds
to separate organelles
according to their density
Differential
centrifugation
Supernatant first out (spun at
lowest speed) is most dense =
nuclei
spun at higher speeds
chloroplasts -> mitochondria ->
lysosomes -> RER/SER ->
ribosomes (least dense)
Binary Fission
Involves circular DNA &
plasmids replicating
cytokinesis creates two
daughter nuclei
each daughter cell has one copy
of circular DNA and a variable
number of plasmids
Cell cycle
1) Interphase (G1, S, G2)
2) nuclear division - mitosis or
meiosis
3) cytokinesis
Interphase
Longest stage in the cell cycle
when DNA replicates (S-phase)
and organelles duplicate while
cell grows (G1&G2-phase)
DNA replicates and appears as
two sister chromatids held by
centromere
Mitosis
One round of cell division
two diploid, genetically
identical daughter cells
growth and repair (e.g. clonal
expansion)
comprised of prophase,
metaphase, anaphase and
telophase
Prophase
Chromosomes condense and
become visible
nuclear envelope disintegrates
in animals - centrioles separate
& spindle fibre structure forms
Metaphase
Chromosomes align along
equator of cell
spindle fibres released from
poles now attach to centromere
and chromatid
Anaphase
Spindle fibre contracts (using
ATP) to pull chromatids,
centromere first, towards
opposite poles of cell
centromere divides in two
Telophase
Chromosomes at each pole
become longer and thinner
again
spindle fibres disintegrate +
nucleus reforms
Mitotic index
Used to determine proportion of
cells undergoing mitosis
Calculated as a percentage OR
decimal
mitotic index = cells in visible mitosis/ total X 100
Fluid mosaic
model
Describes the lateral movement
of membranes
with scattered embedded
intrinsic and extrinsic proteins
membrane contains
glycoproteins, glycolipids,
phospholipids and cholesterol
Phospholipids
in membranes
Phospholipids align as a bilayer
hydrophilic heads are attracted
to water
hydrophobic tails repelled by
water
Cholesterol
Present in eukaryotic organisms
to restrict lateral movement of
the membranes
adds rigidity to membraneresistant to high temperatures
& prevents water + dissolved
ions leaking out
Selectively
permeable
membrane
Molecules must have specific
properties to pass through
plasma membrane
lipid soluble (hormones e.g.
oestrogen)
very small molecules
non-polar molecules (oxygen)
Simple
diffusion
Net movement of molecules
from an area of higher
concentration to an area of
lower concentration
until equilibrium is reached
passive
Facilitated
diffusion
Passive process using protein
channels/carriers
down the concentration
gradient
used for ions and polar
molecules e.e sodium ions
and large molecules e.g. glucose
Osmosis
Net movement of water
from an area of higher water
potential to an area of lower
(more negative) water potential
across a partially permeable
membrane
Water
potential
The pressure created by water
molecules
measured in kPa and
represented by symbol ψ
pure water has a water potential
of 0kPa
the more negative the water
potential, the more solute must
be dissolved
Hypertonic
solution
When the water potential of a
solution is more negative than
the cell
water moves out of the cell by
osmosis
both animal and plant cells will
shrink and shrivel
Hypotonic
solution
When the water potential of a
solution is more positive (closer
to zero) than the cell
water moves into the cell by
osmosis
animal cells will lyse (burst)
plant cells will become turgid
Isotonic
When the water potential of the
surrounding solution is the
same as the water potential
inside the cell
no net movement in water
cells would remain the same
mass
Active
transport
The movement of ions and
molecules from an area of lower
concentration to an area of
higher concentration using ATP
and carrier proteins
carrier proteins act as selective
pumps to move substances
Role of carrier
protein in active
transport
When molecules bind to the
receptor - ATP will bind to
protein on inside of membrane
and is hydrolysed to ATP / Pi
protein changes shape and
opens inside membrane
Co-transport
The movement of two
substances across a membrane
together, when one is unable to
cross the membrane itself
involves a cotransport protein
involves active transport
e.g. absorption of
glucose/amino acids from
lumen of intestines
Antigens
Proteins on the cell-surface
membrane
trigger an immune response
when detected by lymphocytes
Molecules
lymphocytes
identify
Pathogens (bacteria, fungi,
viruses)
cells from other organisms of
same species (transplants)
abnormal body cells (tumour
cells)
toxins (released from bacteria)
Antigenic
variability
When pathogenic DNA mutates
causing a change in shape of
antigen
previous immunity is no longer
effective as memory cells don’t
recognise new shape of antigen.
specific antibody no longer
binds to new antigen
Phagocytes
Non-specific immune response
phagocytes become antigenpresenting cells after
destroying pathogen
T lymphocytes
Made in bone marrow and
mature in thymus gland
involved in cell-mediated
immune response
respond to antigen-presenting
cells
Physical
barriers
Anatomical barriers to
pathogens
skin
stomach acid
lysozymes in tears
Role of cloned
T helper cells
Some remain as helper T cells &
activate B lymphocytes
stimulate macrophages for
phagocytosis
become memory cells for that
shaped antigen
become cytotoxic killer T cells
Antigenpresenting
cells
Any cell that presents a non-self
antigen on their surface
infected body cells
macrophage after
phagocytosis
cells of transplanted organ
cancer cells
Cytotoxic
T cells
Destroy abnormal / infected
cells by releasing perforin
so that any substances can
enter or leave the cell and this
causes cell death
Role of T
helper cells
Have receptors on their surface
that attach to antigens on APCs
become activated - clonal
selection
B lymphocytes
Made in bone marrow and
mature in bone marrow
involved in humoral immune
response
involves antibodies
Humoral
response
APC activates B cell
B cell undergoes clonal
selection and expansion - rapid
division by mitosis.
differentiate into plasma cells /
memory B cells
plasma cells make antibodies
Antibodies
Quaternary structure proteins
made of four polypeptide chains
different shaped binding site =
variable region
complementary to a specific
antigen
end is antigen binding site on variable region, entire variable region is light chain, rest of body is heavy chain
B memory cells
derived from B lymphocytes
remember specific antibody for
particular antigen
will rapidly divide by mitosis
and differentiate in plasma
cells upon secondary encounter
resulting in large numbers of
antibodies rapidly
Agglutination
Antibodies have two binding
sites and are flexible - clumps
pathogens together
makes it easier for phagocytes
to locate and destroy pathogen
Passive
immunity
Antibodies introduced into body
plasma and memory cells not
made as no interaction with
antigen
short-term immunity
fast acting
Natural active
immunity
After direct contact with
pathogen through infection
body creates antibodies and
memory cells
Active
immunity
Immunity created by own
immune system - antibodies
made
exposure to antigen
plasma and memory cells made
long term immunity
slower acting
Vaccinations
Small amounts of dead or
attenuated pathogens injected /
ingested
humoral response activated
memory cells are able to divide
rapidly into plasma cells when
re-infected
Artificial active
immunity
Creation of antibodies and
memory cells following
introduction of an attenuated
pathogen or antigens
vaccination
Primary vs
Secondary
response
Primary = first exposure to the
pathogen
longer time for plasma cell
secretion & memory cell
production
for the secondary response,
memory cells divide rapidly into
plasma cells
so a large number of antibodies
made rapidly upon reinfection
Monoclonal
antibodies
A single type of antibody that
can be isolated and cloned
antibodies that are identical -
from one type of B lymphocyte
complementary to only one
antigen
Herd
immunity
When enough of the population
is vaccinated so pathogen is not
transmitted and spread easily
provides protection for those
without vaccine
Uses of
monoclonal
antibodies
Medical treatment - targeting
drugs by attaching antibody
complementary to tumour cell
antigen
medical diagnosis - pregnancy
tests
Pregnancy test
ELISA test which uses 3
monoclonal antibodies and
enzymes to test for hCG
Purpose of
ELISA test
Detect the presence and
quantity of an antigen
used for medical diagnosis. Eg.,
HIV
HIV structure
Core = RNA and reverse
transcriptase
capsid = protein coat
lipid envelope taken from hosts
cell membrane
attachment proteins so it can
attach to Helper T cells
Ethical issues
with monoclonal
antibodies
Requires mice to produce
antibodies and tumour cells
requires a full cost-benefit
analysis
HIV replication
Attaches to CD4 receptor on
helper T cells
protein fuses with membrane
allowing RNA + enzymes to enter
reverse transcriptase makes
DNA copy and this is inserted
into nucleus
nucleus synthesises viral
proteins
Why vaccines
may be unsafe
Inactive virus may become
active - viral transformation
non-pathogenic virus can
mutate and harm cells
side effects of immune
response
people may test positive for
disease
Auto
Immunodeficiency
Syndrome (AIDs)
When HIV has destroyed too
many T helper cells, host is
unable to produce adequate
immune response to other
pathogens
host susceptible to
opportunistic infections
Role of
antibodies in
ELISA
First antibody added is
complementary to antigen in
well - attaches
second antibody with enzyme
added which attaches to first
antibody as complementary.
when substrate solution added
enzyme can produce colour
change
Pathogens
Microorganisms that cause a
disease
by releasing toxins or killing
cells / tissues
Why do you
wash well in
ELISA
Removes unbound 2nd
antibodies
otherwise enzyme may be
present → colour change →
false positive
Why are
antibiotics
ineffective against
viruses?
Viruses are inside host cells
where antibiotics cannot reach
antibiotics affect parts of
bacteria that viruses do not
have (e.g the cell wall)
Cytokinesis
Final stage in the cell cycle
when the cytoplasm splits in
two
creates two new cells
Uncontrolled
mitosis
Uncontrolled cell division can
lead to the formation of
tumours and of cancers
many cancer treatments are
directed at controlling the rate
of cell division
Viral
replication
Following injection of their
nucleic acid
the infected host cell replicates
the virus particles
Cell adaptations for
rapid transport
across membranes?
Increase in surface area or
membrane
increase in the number of
protein channels and carrier
molecules in the membranes
antigen antibody complex
when a complementary antibody binds to an antigen
clumps pathogens together (agglutenation)
