Unit 1 - Cells

image / actual

scale bar measurement / scale bar label

1. all living things are composed of cells
2. the cell is the smallest unit of life
3. cells only arise from pre-existing cells

challenges the idea that cells only have one nucleus
- muscle cells have more than one nucleus

challenges the idea that living structures are composed of discrete cells
- fungal hyphae are very large with mny nuclei and continuous cytoplasm (not a single unit)

challenges the idea that cells must be simple in structure and small in size
- acetabularia is a single-celled organism that is very large in size
- also complex in form

metabolism, response, homeostasis, growth, excretion, nutrition

the web of all enzyme catalysed reactions in a cell

living things can respond to and interact with their environment

the maintenance and regulation of internal cell conditions

living things can grow/ change size or shape

the removal of metabolic waste

living things produce offspring, sexually of asexually

feeding by either the synthesis of organic molecules or the absorption of organic matter

- shorter diffusion pathways
- concentration gradients to be easily generate

molecules have to travel a shorter distance

less solute is needed

divide

high SA:vol ratio

interaction of component parts
- multi cellular organisms are capable of performing functions that individual cells cannot undertake
- this is due to the interaction between cells producing new functions

stem cells can continuosly divide and replicate

potency

can form into any cell type, as well as extra-embryonic tissue

can form any cell type

can form into many cell types

cannot differentiate, but capable of self-renewal

- a reccesive genetic condition
- causes active transport protein on photoreceptor cells to malfunction
- photoreceptor cells degenerate, and will cause progressive, and eventually total loss of central vision
- embryonic stem cells can be treated to differentiate into retinal cells, which can be injected into the retina to improve vision

- cancer of the blood or bone marrow
- results in poorly-functioning white blood cells
- haematopoetic stem cells (HSCs) are harvested
- chemotherapy and radiotherapy are used to destroy the diseased white blood cells
- HSCs are transplanted back into the bone marrow, HSCs differntiate to form new healthy white blood cells

- simple structures
- no nucleus
- small
- 70s ribosomes
- unicellular
- no organelles
- formed by binary fission

- complex structure
- has a nucleus
- larger in size
- 80s ribosomes
- has membrane bound organelles
- formed by mitosis and meiosis

site of ATP production by aerobic respiration

- contains DNA in the form of chromosomes
- site of ribosome assembly

site of photosynthesis and hence where glucose is produced

made of cellulose, which ensures that it is permeable, strong, and hard to digest

found in cytoplasm and is used to make proteins for use within the cell

- bounded ribosomes
- makes proteins which are transported to be used outside of the cell
- organelle is found close to the nucleus
- synthesizes proteins which are transported by vesicles to the golgi apparatues for modification before secretion outside of the cell

- found close to the plasma mebrane
- consists of flattened membrane sacs called cisternae
- does not have attatched ribosomes
- FUNCTION: processes proteins from the rER, which are repackaged in the vesicles for secretion outside of the cell

singles membrane with fluid inside, used to transport materials inside of a cell

formed from the golgi apparatus, contains digestive enzymes for the breakdown of:
1. ingested food in vesicles
2. unwanted organelles
3. the cell itself
has a high concentration of enzymes which causes the organelles to stain heavily

single membrane with fluid inside, large and permanent in plant cells
FUNCTION: maintain hydrostatic pressure

thin projections from the cell surface, contains microtubules, used for locomotion of the cell (animal cells only)

thin projections from the cell surface, used to move the cell (animal cells only)

phosphate head of a a phospholipid

fatty acid tails of a phospholipid

joins 2 cells together

localises membrane pathways

facilitated and active diffusion
- channels or FD, pumps for AD

markers of cellular recognition

attatchement points for cytoskeleton and extracellular matrix

receptors for peptide hormones

permanently attached to the membrane and are typically transmembrane (they span across the bilayer)

proteins which have a temporary association with the membrane by non-covalent interactions and associate with one's surface of the membrane

proteins with an oligosaccharide chain attatched
- importatnt for cell recognition by the immune system and hormoe receptors

makes the phospholipds packed more tightly and regulates the fluidity and flexibility of the membrane

ensures that the cell can move and the required substances can move across the plama membrane

- membrane proteins from two different cells were tagged with red and green fluorescent markers respectively
- when the two cells were fused, the markers became mixed throughout the membrane of the fused cell
- this demonstrated that the membrane proteins could move and did not form a static layer (as per Davson-Danielli)

freeze fracturing was used to split open the membrane and revealed irregular rough surfaces within the membrane
these rough surfaces were interpreted as being transmembrane proteins, demonstrating that proteins were not solely localised to the outside of the membrane structure

- proteins were embedded within the lipid bilayer rather than existing as separate layers
- the phospholipid bilayer is viscous and individual phospholipids can move position and is embedded with proteins, resulting in a mosaic of components

phospholipids, choloestrol, proteins

the model was described as a 'lipo-protein sandwich’, as the lipid layer was sandwiched between two protein layers (electron micrograph)

- It assumed all membranes were of a uniform thickness and would have a constant lipid-protein ratio
- It assumed all membranes would have symmetrical internal and external surfaces (i.e. not bifacial)
- It did not account for the permeability of certain substances (did not recognise the need for hydrophilic pores)
- The temperatures at which membranes solidified did not correlate with those expected under the proposed model

along the concentration gradient, does not require energy
- simple diffusion
- osmosis
- facilitated diffusion

involves the movement of materials against the concentration gradient
- primary: use of ATP to mediate transport
- secondary: coupling with another molecule

the passive net movement of particles from areas of high concentration to low concentration, often through a partially permeable membrane

concentration gradient, surface area, length of diffusion path

the passive movement of molecules across the cell membrane via the aid of a membrane protein
- carrier proteins
- channel proteins
- potassium proteins

- uniport (one substance)
- symport (two different substances in the same direction)
- antiport (two different substances in opposite directions)

the net movement of water molecules across a partially permeable membrane from a region of low solute concentration to high solute concentration

integral proteins, acts as a pore in the membrane that speeds the movement of water molecules

use the energy from the hydrolysis of ATP to move ions or large molecules across the cell membrane

results in three sodium ions being pumped out of hte axon and two potassium ions being pumped in

bud off the rER and golgi apparatus, carry proteins produced by ribosomes on the rER to the golgi apparatus where they are prepared for expoer from the cell via another vesicle

taking in of external substances by an inward pouching of the plasma membrane, forming a vesicle

the way in which solid substances are ingested

the way in which liquid substances are ingested

release of substances from a cell when a vesicle joins with the cell membrane
- vesicles (golgi) fuse with the plasma membrane, expelling their contents into the extracellular environment

animal cells - shrivel
plant cells - plasmolysed

animal cells - stay the same
plant cells - flaccid

animal cells - lysis
plant cells - turgid

theory that living cells arose from non-living matter

1) water was boiled to a vapour
2) the vapour was mixed with hydrogen gas, methane, and ammonia
3) the mixture of gases was then exposed to an electrical discharge to stimulate lightning
4) once the mixture was allowed to cool, it was found to have traces of organic molecules

living things only arise from other living things by reproduction

- using swan neck flasks
- these flasks were filled with broth
- the neck of these flasks prevented external dust particles from entering
- the broth was then boiled to kill any pre-existing micro organisms
- the neck of the flask was then broken and exposed to the air particles, resulting in the growth of bacteria from external contaminants

eukaryotic cells are believed to have evolved from early prokaryotes that were engulfed through phagocytosis
- EVIDENCE
1) double membranes
2) 70s ribosomes
3) suseptible to antibiotics
4) divide by binary fission
5) naked and circular DNA

prepares for cell division
- G1 phase: cell functions normally, protein synthesis
- S phase: genetic material is duplicated, DNA replication
- G2 phase: microtubles are produced

prophase, metaphase, anaphase, telophase

- chromatin condense
- nuclear membrane disappears

- nuclear membrane completely breaks down
- chromosomes line up along the equitorial plate
- spindle fibres attatch to the centromere of the chromosomes

- spindle fibres contract, separating the generally identical chromatids
- the chromatids move to opposite poles of the cell

- spindle fibres dissolve
- chromosomes de-condense
- nuclear membrane forms around each set of chromosomes

the splitting of a cell into two genetically identical cells

- microtubule filaments form around the centre of the cell
- the filaments contract to form a cleavage furrow
- once the furrow meets, the cell is separated into two daugter cells

- vesicles build along the equitaorial plate of the cell
- these vesicles fuse together to form a cell plate, which extends outwards
- this separates the cell into two daughter cells

cells in mitosis / total number of cells

regulatory proteins which control the cell cycle
- cyclins and cyclin dependent kinases (CDKs) bind together to form a complex
- this complex will bind and modify a protein via phosphorylation
- the phosphorylated protein will trigger an event in the cell cycle, then the cyklin will be degraded and be inactive

- uncontrolled cell division leads to the formation of tumours
- a mutagen in the oncogene will cause a malfunction in the cell cycle, leading to uncontrolled cell division which forms a tumour

agent that changes the genetic material of an organism

a cancer causing gene

- a primary tumour grows at its site
- cancerous cells from this tumour detatch and circulate around the body
- these cells invade tissue and divide continously to form secondary tumours