Cells Flashcards
what happens in complex multicellular organism with eukaryotic cells?
eukaryotic cells become specialized for specific functions. specialized cells are organized into tissues, tissues into organs, organs into s ystems
What is a stem cell?
Undifferentiated cells that can differentiate into specialised cells or make copies of themselves
What is differentiation?
cell develops specific adaptation, to carry out to a particular function
What is a cell that photosynthesise?
Palisade cell
What is the difference between a phagocyte nucleus?
lobed nucleus
How is a sperm cell specialised?
- nucleus contains DNA, is located in the head
- tail for swimming
- full of mitochondria, this supplies energy for movement
- acrosome, containing enzymes to break down the eggs cell membrane, so it can penetrate
How is a root hair cell specialised?
- large surface area, increased rate of absorption
- long
- lots of mitochondria, for active transport of mineral ions from soil, into roots
Categories of differentiation
- increased/decreased in number of a particular organelle e.g. loss of nucleus in a red blood cell
- change in shape of the cell
- combination of all three
what is the structure and function of a slime capsule
sticky coat outside cell wall to protect it from drying out
what is the structure and function of a flagellum?
thin fibers, propel bacteria in different directions, which makes them motile (swim)
what is the structure and function of a nucleoid?
place in cytoplasm where genetic material is found
what is the structure and function of a mesosome
Inner extension of the cell surface membrane where respiration occurs
what is the cell wall made out of in a prokaryotic cell?
peptidoglycan, makes it rigid
structure and function of a plasmid
smaller rings of DNA that often contain genes of antibiotic resistance
difference between a prokaryotic and eukaryotic cell?
- genetic information is not enclosed within a nuclear membrane
- no membrane bound organelles
- smaller ribosomes
- cell wall that contains murein a glycoprotein
additional sub cellular structures in prokaryotic cells
- one or more plasmids
- a capsule surrounding the cell
- one or more flagella
what is resolution?
ability to distinguish two points as being separate
what is the resolution of a light microscope?
200nM due to the wavelength of light
how to work out total magnification
objective lens x eye piece lens
ol - x4 x10 x100
epl - x10
what is the problem with sectioning in light microscopes?
what is the solution?
material distorts when cut into thin sections
specimens are embedded in wax to support tissue as it is cut
what is the problem with staining in light microscopes?
what is the solution?
a lot of biological material is colorless
- stains are added that bind to the specimen allowing detail to be seen
- some stains are specific to certain cell structures
how does the sample have to be in a light microscope?
thin so the light can pass through
how to find one graticule division
number of micrometres ÷ number of graticule division
how to find the measurement (µm)
graticule divisions x magnification factor
what is magnification?
how many times bigger the image of a specimen is compared to the actual size
why cant a phospholipid bilayer be observed under a microscope?
- width of bilayer is 10nm
- The maximum resolution of a light microscope is 200nm
- Any points that are separated by a distance less than 200nm can’t be resolved by a light microscope
How does a bacteria reproduce
Binary fission
Stages of binary fission
- DNA must be replicated
- Parent cell divides to give two daughter cells each with the same circular DNA
Why are viruses referred to as acellular?
As they are not living, not a cell and have minimal sub-cellular structures
What are the structures on all viruses?
- protein coat ~ protects genetic info
- attachment protein ~ enables virus to enter host cells
- genetic material
Additional structures on viruses
- lipid envelope
- enzyme
- matrix
- capsid
what happens in a transmission electron microscope?
beam of electrons passes through a thin section of a specimen. areas that absorb the electrons appear darker on the electron micrograph that is produced
what happens in an scanning electron microscope?
beam of electrons pass across the surface and scatter. the pattern of scattering builds up a 3d image depending on the contours of the specimen
limitations of SEM & TEM
- whole system must be in a vacuum so living specimens cant be observed
- specimens have to be very thin
- SEM has a lower resolution
How to find out the magnification from the scale factor
Measure the scale factor length / scale factor
Resolution of an electron microscope?
0.2 nm this allows you to see the internal structure of organelles (aka cell ultra structure)
Why do electron microscopes have high resolutions
Due to the short wavelength of electrons
What are tem used to view
The ultra structure of cells in very thin sections of material (2D image)
What are SEM used to view
The surface detail of specimens (3D image)
negative features of electron microscopes
- both require complex processing of the specimen which can introduce artefacts
- due to the vacuum in the microscopes all specimens must be dead
- coloured images are not obtained (false colour added after the image is obtained)
What is cell fractionation
process where cells are broken up and the different organelles they contain separated out.its a two stage process: homogenisation and ultra centrifugation
Why do people use cell fractionation
study cell structure and function
What happens before cell fractionation can begin
Tissue is place in cold, isotonic buffer solution
Why does the cell fractionation have to be placed in this solution
Cold - reduces activity of enzymes which may break down organelles
Isotonic - prevent organelles bursting/shrinking due to osmotic loss/gain of water
Buffered- maintain a constant pH to avoid damage to organelles
Steps of cell fractionation and ultra centrifugation
- Homogenisation sample placed in a cold, isotonic buffered solution
- Goes into a homogeniser
- Filtration removes cellular debris and whole organelles to make a pure solution
- Homogenise is centrifuged
- Sample is spun at low speed, high density organelles in formed in a sediment pellet. E.g. nucleus
- Segments pellet is removed
- Sample is spun at a higher speed, sediment pellet is formed e.g mitochondria and chloroplast
Why do cells need to divide:
To produce new cells
- for growth
- for replacement of old cells
To reproduce
- for asexual reproduction
- to produce gametes for sexual reproduction
Mitosis
Produces cell that are genetically identical for:
- growth
- replacement
- asexual reproduction
Meiosis
Produces cells that are genetically different
- I.e. gametes for sexual reproduction
Cell division
What processes result in the division of the nucleus?
What happens after this?
- mitosis & meiosis are processes that result in the division of the nucleus
- this is followed by division of the cytoplasm - cytokinesis
Interphase
- the phase between divisions
- includes G1, s and G2
What happens during G1 phase:
- cell growth
- new organelles formed
- proteins synthesised
What happens during S phase:
- DNA synthesis
- the DNA sis replicated so the amount of DNA double
What happens during G2 phase:
Proteins synthesised
What are tumours?
Tumours are the result of uncontrolled division of genetically abnormal cells
Mutations:
- mutations in DNA occur often and most are harmless
- if the mutation is in a cancer gene then this may lead to the formation of a tumour
What do oncogenes do?
Start the cell division process
What do tumour-suppressor genes do?
Switch off cell division
Causes of cancer
- ionising radiation
- inherited defect genes
- viruses
- dietary factors
- environmental poisons
how does the treatment of cancer work
blocking some part of the cell cycle
drugs used to treat cancer (chemotherapy) disrupt the cell cycle by:
- preventing DNA from replicating e.g. cisplatin
- inhibiting metaphase by interfering with spindle formation e.g. vinca alkaloids
what is the problem with chemotherapy drugs?
they disrupt the cell cycle of normal cells
when cells aren’t dividing what do chromosomes exist as?
chromatin.
number of chromosomes varies between species
what is chromatin
loosely coiled DNA and associated histone proteins
what happens during cell division with chromatin
it supercoils and condenses so the chromosomes become visible
homologous chromosomes
sex chromosomes are non-homologous in one gender . they are homologous in females XX and non in males XY. in other species it will be different
structure of chromosomes?what does it contain?
centromere
sister chromatids
what is a centromere?
part of a chromosome that links sister chromatids
what are sister chromatids?
duplicated chromosomes attached by a centromere. after anaphase the sister chromatids separate and are known as chromosomes
what is a centrosome in animal cells
where two centrioles are held by a protein mass
phases in mitosis?
- telophase
- prophase
- metaphase
- anaphase
what happens during interphase
- organelles multiply
- chromosomes are copied
what happens during prophase
- chromosomes condense
- nuclear membrane breaks down
- centrioles move to poles and spindle fibres start to form
what happens during metaphase
- chromosomes line up at the equator of the cell
- chromosomes attach to spindle fibres via the centromere
what happens during anaphase
- spindle fibers shorten and separate the sister chromatids
- each chromosome moves to an opposite pole of the cell
What happens during telophase
- chromosomes reach the poles of the cells
- nucleus enevelope begin to reform
- chromosomes begin to decondense
- spindle fibres break down
What happens during cytokinesis
- cytoplasm and cell membrane divide
- two genetically identical daughter cells are formed
What is the equation for the mitosis index?
Number of cells in mitosis / total number of cells x 100
what are the functions of phospholipids in the membrane
- allow lipid-soluble substance to enter and leave a cell
- prevent water soluble substances leaving the cell
- makes the membrane flexible and self-sealing
what is fluidity in a membrane controlled by:
- amount of cholesterol
- length of fatty acid chains - the shorter increases fluidity
- proportion of saturated and unsaturated fatty acids - saturated fatty acids decrease fluidity
how wide are membranes
always 7nm
where are protein contained in a membrane
phospholipid membrane
types of proteins in a membrane
- extrinsic proteins~ occur in the surface of the lipid bilayer. e.g. receptors or for mechanical support
- intrinsic proteins ~ span from one side of the phospholipid bilayer to the other. e.g. protein channels, carrier proteins
membrane protein functions
- ion channels~ allow water soluble molecules/ions through
- transport proteins~ transport specific molecules
- glycoproteins~ protein with a polysaccharide chain extending outwards, involved in cell recognition
- receptors~ binding sites for hormones
where would you find cholesterol molecules
randomly distributed across the bilayer between phospholipids
cholesterol functions
- helps regulate fluidity of the membrane
- prevents polar molecules passing through
- acts to stabilise the phospholipids
what are glycoproteins and glycolipids
carbohydrate chains attached to proteins or lipids
functions of glycoproteins and glycolipids:
- helps cell attach to each other
- acts as cell surface receptors (e.g. fro neurotransmitters, hormones)
- allows cells to recognize each other (e.g. lymphocytes)
features in a phospholipid bi layer?
- cholesterol
- hydrophilic head
- hydrophobic tail
- carrier proteins
- channel proteins
- carbohydrates
- glycoproteins
- glycolipid
fluid mosaic model of a plasma membrane
why is it described as fluid?
- individual phospholipid molecules and proteins can move relative to one another
- allowing the membrane to constantly changes shape
fluid mosaic model of a plasma membrane
why is it described as mosaic?
- the proteins in the membrane vary in size and shape
- this creates a mosaic like pattern
active transport
what does it require?
examples
requires energy inform of ATP
- active transport
- bulk transport
passive transport
what does it require?
examples
no energy required form ATP, only requires kinetic energy of particles
- diffusion
- facilitated diffusion
- osmosis
what is the one factor that effects the rate of diffusion
permeability of the membrane to that substance
what is simple diffusion?
molecules that can diffuse down a concentration gradient through the phospholipid bilayer, they must be non-polar or small
e.g. o2, co2 urea
factors that affect the rate of diffusion
- temperature
- surface area
- concentration gradient
- size of the molecule
- chemical nature of molecule
rate of diffusion
temperature
as temp increases the particles have more kinetic energy so they move around more
rate of diffusion
surface area
the less space they have to diffuse the lower the rate
rate of diffusion
concentration gradient
the steeper it is, the faster the rate as there are more collisions
rate of diffusion
size of the molecule
larger molecules decrease the rate as they have a larger mass, its harder to pass through
rate of diffusion
chemical nature of the molecule
polar molecules are repelled by the hydrophobic tails in the bilayer, decreasing the rate
what is facilitated diffusion
molecules e.g. ions (Na+) and hydrophilic molecules (e.g. glucose & amino acids) require carrier or channel proteins to pass through the membrane . they travel down the concentration gradient
what do channel protein’s do?
- form aqueous pores in the membrane
- allows water soluble molecules to pass through the hydrophobic core of the bilayer
What do carrier proteins do?
- molecules fits into the protein
- protein changes shape and molecule passes through
What are the proteins specific for?
The molecule being trapsorted
Wha affects the rate at which molecules move by facilaitated diffusion
It’s affected by the same factors that affect diffusion but alas the availability of carrier/ channel proteins
What are the two types of active processes?
- active transport
- bulk transport
What are the differences between active transport and facilitated diffusion
Active transport is:
- against a concentration gradient
- requires energy
- uses carrier proteins
Features of active transport
- use carrier proteins
- substances are transported against the concentration gradient
- requires energy in the form of ATP
- substances are transported more quickly than by diffusion
The process of active transport
- The molecule binds to complimentary a site on the carrier protein
- ATP is hydrolysed to ADP and the carrier protein changes shape
- Molecule transported across the membrane
- One way flow as molecules can only fit into the carrier protein on one side of membrane
Features of bulk transport
- moving large amounts
- endocytosis (in) and exocytosis (out)
- can occur due to ability fm membranes to fuse and pinch off
- active process requiring ATP
Examples of bulk transport
- release of hormones , e.g. insulin into the blood
- plant cells - vesicular carrying materials to make a cell wall
Phagocytes - engulfing pathogens and fusion with lysosomes
Thee two types of endocytosis (in)
Phagocytosis
Pinocytosis (cell drinking)
What is phagocytosis
Solid substances are taken into a cell via an unfolding of the surface membrane
What is pinocytosis
Similar to phagocytosis, but the unfolding in the membrane are smaller and liquids are taken in
What is exocytosis (exit)
Vesicles move towards the surface membrane, fuse with it, and release their content outside the cell
What is co- transport important in
In the absorption of glucose in the small intestine
Features of the small intestine
- has walls that are 1 cell thick, short diffusion pathways
- microvilli - increases surface area
- close to capillaries - lots of capillaries, good blood supply ,makes. Good concentration gradient
What 3 process does absorption involve
- diffusion
- facilitated diffusion
- con transport
The process of active transport in epithelium cells
- active transport of sodium ions from epithelial cell in blood lowers the sodium concentration in the cell
- generates a concentration gradient between ileum and the epithelial cell
- Na+ move into the cell from the ileum by facilitated diffusion, carrying glucose molecules along with them via a cotransport protein
- glucose concentration increases in epithelial cell, glucose molecules enter blood via facilitated diffusion
Features of water potential
- measure of water concentration
- measure of KPa
- pure water has the highest waters potential
- adding solute to the water decrease (makes more negative) the water potential
Definitions of osmosis
Is the net movement of water molecules from a region of higher water potential to a region of lower water potential across a partially permeable membrane
The effect of solute on water concentration
The greater the solute concentration, the lower the water potential
What is hypotonic?
A region of higher water potential (lower solute concentration)
What is hypertonic?
A region of lower water potential (higher solute concentration)
What is isotonic?
A region where there are equal water potential on either side of a membrane
What happens with a hypotonic solution in an animal cell
Water potential of cell is lower than the external solution
-> water enters by osmosis and eventually the cell bursts
What happens with a hypertonic solution in an animal cell
Water potential of the cell is higher than the external solution
-> water leaves the cell by osmosis and the cell shrinks
What happens with a isotonic solution in an animal cell
Water potential of cell the same as the external solution
-> water enters and leaves at the same rate = dynamic equilibrium
What happens in a hypotonic solution in a plant cell
Water enters by osmosis
-> as water enters tutor pressure increases and resists further entry
Cell is turgid
What happens in a hypertonic solution in a plant cell
Water leaves by osmos
-> eventually the membrane pulls way from the cell wall (plasmolysis)
Cell is flaccid
What happens in a isotonic solution in a plant cell
No net movement of water
-> cell stays the same
What in incipient plasmolysis
The term used to describe when 50% of the cells have undergone plasmolysis
cell surface membrane
take up fluid/solid material to form membrane bound vesicles
lysosomes membrane
contains enzymes for the destruction of waste/ foreign materials . periosomes are the site for destruction
mitochondria membrane
energy transfer, where cellular respiration and photosynthesis takes place and regulates the reactant usage
nucleus membrane
nuclear envelope of two membranes form a separate compartment, for the cell, genetic material so it doesn’t get damaged
vesicles membrane
moves substance in and out of the cell. produces lysosomes and compartmentalize modification
process of binary fission
- Circular DNA replicates and attach to cell membrane. Plasmids replicate.
- Cell membrane grows between two DNA molecules and pinches inwards, dividing the cytoplasm in two.
- cell wall forms between the 2 DNA molecules.
Whats the difference between ribosomes in the RER or in the cytoplasm
RER - produces proteins that are being exported from the cell e.g. hormones
cytoplasm - produces proteins for the internal cell
Explain why the student used only the first 5 mm from the tip of an onion root
Where mitosis occurs
