Topic 1- cell biology Flashcards
the 3 ideas of cell theory
- all living things are composed of cells (or are cell products)
- the cell is the smallest unit of life
- cells only arise from pre-existing cells
Striated muscle
- challenges the idea that a cell has one nucleus
- muscle cells have more than 1 nucleus per cell
Aseptate fungal hyphae
- challenges the idea that a cell is a single unit
- like muscle cell, they are multi nucleated
- fungi may have filamentous structures called hyphae which are separated into cells by internal walls (septa)
Giant algae (acetabularia)
- challenges both the idea that cells must be simple in structure and small in size/idea that larger organisms are always made up of many microscopic cells
- gigantic in size
- complex in form
The 7 basic functions of life
- metabolism (undertake essential chemical reactions)
- response (responsive to internal and external stimuli)
- homeostasis (the maintenance & regulation of internal cell conditions)
- growth (can move, change in size and shape)
- excretion (removal of metabolic waste)
- reproduction (produce offspring either sexually or asexually)
- nutrition (exchange materials & gas with the environment)
Unicellular organisms (must be able to carry out all the life functions): Chlorella
Excretion- controlled by plasma membrane
Metabolism- most metabolic pathways happen in the cytoplasm
Nutrition- photosynthesis happens inside the chloroplast to provide algae with food
Reproduction- binary fission
Growth- gets larger until it divides
Response- moves towards light/changes in the environment
Homeostasis- contractile vacuole fills up with water and expels through plasma membrane to manage water content
(Respiration by diffusion of gases)
Unicellular organism: paramecium
Excretion- controlled by plasma membrane
Metabolism- metabolic pathways happens in the cytoplasm
Nutrition- food vacuoles contain organisms the paramecium has consumed/ feeding using cilia
Growth- gets larger until it divides
Reproduction- binary fission
Homeostasis- contractile vacuole fills up with water and expels it through the plasma membrane to manage the water content
Response- moves towards food/ changes in the environment
(Respiration by diffusion of gases)
Rate of metabolism equation
Mass/volume
Rate of material exchange
= surface area
SA: VOL ratio
As cell grows, volume increases faster than SA
Hence decreased SA:VOL ratio
If metabolic rate exceeds rate of exchange of vital materials and waste, cell will eventually die
Hence growing cells tend to remain small in order to maintain a high SA:VOL ratio suitable for survival
(Indeed small warm blooded mammals lose heat verity quickly due to their large SA:VOL ratio)
Cells & tissues specialised for gas or material exchange will increase SA to promise the transfer of materials, ex) alveoli
Differentiation
- when cells metabolism & shape changes to carry out a specialised function
- the activation of different instructions by chemical signals will cause it to differentiate
- fewer active genes a cell possesses, the more specialised it will become
- inactive genes are mainly packaged in a condensed form (heterochromatin)
Stem cells
- are unspecialised cells that can continuously divide & replicate
- have capacity to differentiate into specialised cell types
Totipotent
Pluripotent
Multipotent
Unipotent
: can differentiate into any type of cell
: can differentiate into many types of cells
: can differentiate into a few closely related types of cell
: can regenerate but can only differentiate into their associated cell type, ex) liver cells
Stargardt’s macular dystrophy
- recessive genetic condition
- causes progressive and eventually total loss of central vision
- embryonic stem cella’s are treated to divide and differentiate to become retinal cells, the retinal cells are injected into the retina. The retinal cells attach to the retina and become functional. Central vision improves as a result of more functional retinal cells.
Leukaemia
- cancer of blood or bone marrow, resulting in abnormally high levels of poorly function white blood cells
- hematopoetic stem cells (HSC) are harvested from bone marrow, peripheral blood or umbilical cord blood
- chemotherapy used to destroy the diseased white blood cells, new white blood cells need to be replaced with healthy cells hence HSCs are transplanted back into the bone marrow where it differentiates to form healthy white blood cells.
- use of a patients own HSCs means there is far less risk of immune rejection compared with traditional bone marrow transplant
Arguments for therapeutic cloning
- transplants are less likely to be rejected as they are cells which are genetically identical to the parent
- transplants do not require death of another human
- stem cells can be taken from embryos that have stopped developing and would have died anyways, ex) abortion
- cells are taken at a stage when embryo has no nervous system and can arguably feel no pain
Arguments against therapeutic cloning
- involves the creation and destruction of human embryos
- religious or moral objections
- embryonic stem cells are capable of continued division and may develop into cancerous cells and cause tumours
Comparison of stem cell sources: embryo
- can be obtained from excess embryos generated by IVF programs
- can only be obtained by destruction of an embryo
- growth potential is almost unlimited
- higher risk of tumour development
- can differentiate into any cell type
- less chance of genetic damage than adult cells
Comparison of stem cell sources: cord blood
- easily obtained and stored, though limited quantities available
- umbilical cord is removed at brith and discarded whether or not stem cells are harvested
- reduced growth potential compared to embryonic cells
- lower risk of tumour development
- limited capacity to differentiate
- less chance of genetic damage that adult cells
Comparison of stem cell sources: adult
- difficult to obtain as there are very few and are buried deep in tissues
- can give permission for cells to be extracted/consent
- reduced growth potential compared to embryonic cells
- lower rick of tumour development
- limited capacity to differentiate
- due to accumulation of mutations through the life of the adult, genetic damage can occur
- fully compatible with the patient as the stem cells are genetically identical
Resolution
The shortest distance between two points that can be distinguished
Prokaryote diagram
Has no nucleus & no membrane bound organelles
Labelled diagram including:
- 70s ribosome
- cell membrane
- plasmid
- cell wall
- nucleoid
- capsule
- flagellum
- pili
Eukaryote diagram
Has nucleus & membrane bound organelles
Labelled diagram including:
- mitochondria
- vesicle
- nucleus
- lysosomes
- cytoplasm
- smooth ER
- Golgi apparatus
- rough ER
- free 80s ribosomes
Process of binary fission
The way in which prokaryotes reproduce asexually
- DNA is duplicated semi conservatively
- Two DNA loops attach to the membrane
- Membrane elongates & pinches off forming two separate daughter cells
Advantage & disadvantage of binary fission
Advantage: quick reproduction
Disadvantage: no/limited variation
Nucleus
- double membrane
- contains genetic information in the form of chromosomes
Mitochondria
- double membrane
- site of ATP production by aerobic respiration
Free ribosomes
- no membrane
- synthesises proteins to function in the cytoplasm
RER
- 80s ribosomes attached to the outside
- synthesises proteins which are transported by vesicles to the Golgi apparatus
Vesicles
- small in size
- used to transport materials inside of a cell
Golgi apparatus
- processes and modifies proteins from the RER
Lysosomes
- contains digestive enzymes that breaks down unwanted/damaged organelles and ingested food
- single membrane
Vacuoles
- storage of water or sugar
- in animals, smelled & temporary
- in plant cells, vacuoles are large & permanent
Flagellum
- used to move the cell
Cilia/pili (animals only)
- used to either move the cell or to exchange genetic materials by attaching to other bacterias
Cell wall
- protects from bursting when under pressure/structural support
Cytoplasm
- where reactions take place
- where genetic material is found
Phospholipid molecule diagram
Labelled with:
- charged phosphate head (hydrophilic)
- non polar lips/fatty acid tail (hydrophobic)
- glycerol
Emergent property of phospholipid molecules
Self organised to keep their ‘heads wet’ and their ‘tails dry’
Integral protein
- permanently embedded
- those that go through all the way through are polytopic (poly= many, topic= surface), those penetrating just one surface are monotopic
Peripheral protein
- temporarily attached by non covalent interactions
Glycoproteins
- proteins with an oligosaccharide chain attached
- important for cell recognition by the immune system & hormone receptors
Cholesterol
- makes the phospholipids pack more tightly & regulates the fluidity & flexibility of the membrane
- reduces permeability to water molecules & ions
- hydroxyl group makes head polar, thus attaches to the phosphate head
Membranes need to be fluid enough so:
- that the cell can move
- that the required substances can move across the membrane
Phospholipid bilayer diagram
Labelled with:
- integral protein
- hydrophobic tail
- hydrophilic head
- peripheral protein
- cholesterol
- glycoproteins
- oligosaccharide chain
Davison & Danielle model
- proposed model where there’s a bilateral of phospholipids in the centre of the membrane with layers of protein on either side, described as ‘lipo protein sandwich’
- draw labelled diagram
Reasons for the model:
- chemical analysis showed that membrane was composed of phospholipid and protein
- evidence suggested that the plasma membrane of red blood cells has enough phospholipids in it to form an area twice as large as the are of the plasma membrane, suggesting a phospholipid bilayer
The evidence:
- in high magnification electron micrograph membranes appeared as two dark parallel line (proteins) with a lighter coloured religion in between (phospholipids), suggesting protein layers on either side of a phospholipid core
Falsification evidence:
- freeze fracturing revealed irregular rough surfaces, interpreted as transmembrane proteins which demonstrated how proteins were not solely localised to the outside of the structure
Singer Nicholson/fluid mosaic model
- biochemical techniques:
Membrane proteins were found to be varied in size & globular in shape, meaning such proteins are unable to form continuos layers on the periphery of the membrane - membrane proteins had hydrophobic regions & therefore would embed in the membrane, not the layer outside
- fluorescent antibody tagging:
Red or green markers attached to antibodies which would bind to membrane proteins. Within 40mins, the red & green markers were mixed throughout the membrane of the fused cell showing that membrane proteins are free to move within the membrane rather than being fixed in a peripheral layer
Diffusion
- passive (requires no energy) net movement of particles from areas of high concentration to low concentration/ down a concentration gradient
Factors affection rate of diffusion
- surface area
- length of diffusion path
- concentration gradient
Facilitated diffusion
- case of diffusion for large & polar molecules through specific protein channels/carries
Carrier proteins
- integral glycoproteins which undergo a conformation change to translocate the solute across the membrane
- specific binding
- slower rate of transport
- may move against the concentration gradient in the presence of ATP
Channel proteins
- integral lipoproteins which contain a pore via which ions may cross from one side of the membrane to the other
- only move molecules along a concentration gradient
- faster rate of transport
- are ion selective & may be gated to regulate the passage of ions
Sodium potassium pump
At rest, SP pump expels sodium ions from the nerve cell whilst potassium ions are accumulated within. When there are relatively more positive charges inside, the potassium channel opens (due to voltage change), allowing potassium ions to diffuse out of the axon. Once the voltage conditions change, the channel rapidly closes again.
Osmosis
- net movement of water molecules across a semi permeable membrane from a region of low solute concentration toa region of high solute concentration
- passive transport
Osmolarity
- measure of solute concentration/number of solute particles
Draw and explain hypertonic, isotonic, hypotonic
Hypertonic:
Solutions with a higher osmolarity than inside the cell
Isotonic:
Same osmolarity/no net water flow
Hypotonic:
Solutions with a relatively lower osmolarity than the inside of the cell
Estimating osmolarity
- by bathing the sample in solutions with known osmolarities
Ex) tissue will lose water when placed in hypertonic solutions——> water loss/gain may be determined by weighing the sample before & after
Isotonic saline
- prevents cellular desiccation
- other usage: rehydration drips, rinse wounds etc..
Draw diagram for uncontrolled osmosis
Animal cell:
Hypertonic- shriveled (crenation)
Isotonic- normal
Hypotonic- Lysed (may burst)
Plant cell
Hypertonic- plasmalysed (cytoplasm will shrink but the cell wall will maintain a structured shape)
Isotonic- flaccid
Hypotonic- turgid (cytoplasm will expand but wont rupture due to the strength of the cell wall)
Active transport
-uses energy to move molecules against a concentration gradient
Primary active transport diagram
Adenosine trip phosphate—> adenosine diphosphate + phosphate (energy)
Sodium potassium pump diagram & explanation
- 3 sodium ions bind to intracellular sites on the SP pump
- A phosphate group is transferred to the pump via the hydrolysis of ATP
- Pump undergoes a conformation change & 3 sodium ions are released
- 2 potassium ions then enter & attach, binding of potassium ions causes release of the phosphate group causing the pump to change shape again
- 2 potassium ions are released and sodium ions can now enter and bind to pump again, hence back to step 1
Endocytosis
- the taking in of external substances by an inward pouching of the plasma membrane, forming a vesicle
- pinocytosis (flui)
- phagocytosis (solid particles)
Exocytosis
- release of substances from a cell (secretion) when a vesicle joins with the cell plasma membrane
Vesicle approaches the plasma membrane and begins to fuse as they share the same properties, membrane pores open allowing the content to pass through.
Biogenesis
Theory that states: cells can only be formed by division of pre-existing cells
Pasteur’s experiments
Method:
- two experiments were set up, in both he placed samples of broth in flasks with long necks which were then melted and bent into a variety of shapes
- some flasks were then heated to kill any organisms/microbes
- fungi & other organisms soon appeared in the unboiled flasks but no in the boiled ones
(Suggested that the broth had to be in contact with air for spontaneous generation)
Conclusion
- rejected the hypothesis of spontaneous generation
- for growth of microbes to occur, a source of contamination is needed
Abiogenesis (non living synthesis)
Theory that living cells arose/formed from non living matter
Theorised four key stages of abiogenesis
- there was non living synthesis of simple organic molecules
- these simple organic molecules became assembled into more complex polymers
- certain polymers formed the capacity to self replicate, enabling inheritance
- formation of membranes to package the organic molecule
Miller Urey experiment
Recreated the postulated conditions of prebiotic earth using a closed system of flasks & tubes
- Water was boiled to vapour, reflecting the high temp common to earths original conditions
- Vapour was mixed with variety of gases to create a reducing atmosphere
- Mixture was then exposed to an electrical discharge (simulating the effects of lightning as an energy source of reactions)
- Mixture was then cooled for 1 week
- Mixture was then examined, found to contain traces of simple organic molecules
(Reducing atmosphere, high temp, electrical discharge. As these do not commonly exist on modern earth, living cells cannot rise independently by abiogenesis)
Endosymbiosis
- larger cell takes in a smaller cell by endocytosis
- smaller cell is not digested but kept alive & performs useful functions for the larger cell
- over generations, the engulfed cell loses its independent utility and becomes a supplement organelle
Evident supporting endosymbiotic theory for mitochondria & chloroplasts
- reproduction of furs via fission like process/grow and divide like cells
- has their own DNA
- susceptible to antibiotics
- has ribosomes similar to prokaryotes (70s)
- some organelles have double membranes
‘Development of Mitochondria’
- an aerobic pro-bacterium enters a larger anaerobic prokaryote
- survives digestion and becomes a valuable endosymbiant
- aerobic pro-bacterium provides a rich source of ATP to its host enabling it to out compete other aerobic prokaryotes
- as host cell grows and divides, the subsequent generations automatically contain aerobic pro-bacterium
- evolves and is assimilated and becomes mitochondrion
Necessity of new cells
- to replace dead, damaged or infected cells
Cell cycle definition
Series of events through which cells pass to divide & create identical daughter cells
Necessity of cell division
- allows for growth
- also used in asexual reproduction
- allows for more cell differentiation
Interphase
Stage in the development of a cell between two successive divisions:
G1- volume of cytoplasm increases
Proteins synthesised
Organelles produced
S- DNA is replicated
G2- cell finishes growing & prepares for cell division
Key processes during interphase
- obtain nutrients
- respiration
- metabolic reactions
- organelles numbers are increased to support the enlarged cell
- DNA is replicated
- protein synthesis
Centromere
Part of chromosome that links sister chromatids
Centrioles
Organise spindle microtubules
Prophase
- DNA supercoils (chromatin condenses and becomes sister chromatids, becomes visible under microscope)
- nuclear membrane breaks down and disappears
- centrosomes move to opposite poles of the cell and spindle fibres Behring to form between them
Metaphase
- spindle fibres from both centrosomes attach to the centromere of each pair of sister chromatids, contraction of the microtubule spindle fibres cause the sister chromatids to line up along the centre of the cell
Anaphase
- continuos contraction of the microtubule spindle fibres causes the separation of sister chromatids
- genetically identical chromosomes move to the opposite poles of the cell
Telophase
- on the 2 chromosomes arrive at the poles, spindle fibre dissolve/disappear, chromosomes decondense to chromatin (no longer visible under microscope)
- nuclear membrane reforms around each chromosome set
Humans
- 23 pairs
- diploid (2n)
Gametes (sex cells- sperm and eggs) are haploid (n)
- half a set as they will pair up with the other half in fertilisation
Cytokinesis in animal cells
- microfilming form a contractile protein/concentric ring around the centre of the cell, pulls the plasma membrane inward
- microfilaments constrict to form a cleavage furrow, when furrow reaches the centre, the cell is pinched apart and two daughter cells are formed
Draw diagram
Cytokinesis in plant cells
- during telophase, membrane enclosed vesicles from the Golgi apparatus migrate to the centre of the cell
- vesicles fuse to form tubular structures, tubular structures merge to form tow layers of plasma membrane called a ‘cell plate’
- the cell plate continues to develop until it connects with the existing cells plasma membrane, this completes the division of the cytoplasm and the formation of two daughter cells
- vesicles deposit, by exocytosis, pectins and other substances in the lumen between the daughter cells form the middle ‘lamella’, to ‘glue’ the cells together
- both daughter cells secrete cellulose to form their new adjoining cell walls
Draw diagram
Mitotic index
Ratio between the number of cells in mitosis and the total number of cells
Cycling
- are proteins that control when the cell moves to the next stage of the cell cycle
- cycling bind to enzymes called cycling dependent kinases, these kinases then become active and attach phosphate groups to other proteins in the cell, the attachment of phosphate triggers the other proteins to become active and carry out tasks
Cyclin D
Triggers cells to move from G0 to G1 and from G1 into S phase
Cyclin E
Prepares the cell for DNA replication in S phase
Cyclin A
Activates DNA replication inside the nucleus in S phase
Cyclin B
Promotores the assembly of the mitotic spindle and other tasks in the cytoplasm to prepare for mitosis
Mutation
- is a change in an organisms genetic code/changes in base sequences of a certain gene can result in cancer
Mutagens
Are agents that cause gene mutations
- chemicals that cause mutations are referred to as carcinogens
- high energy radiation such as xrays
- short wave ultraviolet light
Tumour
- are abnormal growth of tissue that develop at any stage of life in any part of the body (resulting from uncontrolled cell division)
- cancer is a malignant tumour
- Mutation is an oncogene
- Malfunction in the control of the cell cycle
- Uncontrolled cell division
- Tumour formation
Several mutations must occur in the same cell for it to become a tumour, factors other than mutagens that increase the probability:
- the vast number of cells in a human body, the greater the number of cells the greater the chance of mutation
- larger a life span, the greater the chance of mutation
Primary tumour
- malignant tumour growing at the site where the abnormal growth first occurred
- cancerous cells can detach from the primary tumour
- some cancerous cells gain the ability to penetrate the walls of lymph or blood vessels and hence circulate around the body
- circulating cancerous cells invade tissues at different locations and develop into secondary tumours
Oncogene
- a gene that has the potential to cause cancer
Emergent properties & multicellular organism
- arise from the interaction of component part/combination of parts results in new properties emerging/interaction between cells producing new functions
In multicellular organisms:
- cells may be grouped together to form tissues
- organs are then formed from the functional grouping of multiple tissues
- organs that interact may form organ systems capable of carrying out specific body functions
- organ systems collectively carry out the life functions of the complete organism
cell- tissue-organ- system-organism
Ex) muscle- cardiac- heart- vascular- human
