Topic 1 Flashcards
Explain how properties of phospholipids help to maintain the structure of cell membranes
- hydrophobic and hydrophilic regions/amphipathic;
- hydrophobic phosphate ‘heads’ attracted to water and hydrophilic fatty acid ‘tails’ repel water;
- form a bilayer in water with heads in contact with the water on both sides of the membrane/ in contact with the cytoplasm and the environment;
- structure held together by attraction between hypho tails/attraction between heads and water
Explain how the cell cycle is controlled [6]
- cell cycle consists of different phases - G1, S, G2
- cyclins control the cycle
- levels of cyclins rise and fall at different points of the cycle
- regulated by internal and external factors
- different cyclins/four cyclins required to enter different stages of the cell cycle
- cyclins activate cyclin-dependent kinases
- kinases phosphorylate proteins
- phosphorylated proteins perform different functions in cell cycle
Explain the different processes in interphase in a cell [3] (mix of bioninja and MS info)
- G1: synthesis of organelles/protein/cell growth
- S: Replication of DNA
- G2: continued growth of cytoplasm/organelle duplication
According to bioninja the processes occurring in interphase:
DNA replication
Organelle replication
Cytoplasmic volume increase
Transcription/translation - for synthesis of required proteins/enzymes
Obtain nutrients
Respiration - ATP production for mitosis
Processes of cytokinesis in plant and animal cells [4+4]
(bioninja)
Animal:
- after anaphase, microtubule filaments form a concentric ring around the centre of the cell
- filaments constrict so a cleavage furrow forms
- furrow deepens till 2 ends meet -> cells pinched off
- centripetal
Plant:
- centrifugal
- carbohydrate rich vesicles align at centre of cell
- fuse to form early cell plate
- builds outwards and fuses with the cell walls –> separates the 2 cells
Exceptions to cell theory
- Striated muscle cell: multinucleated, very large (‘refutes’ - cells always function as autonomous units)
- giant algae: very large, complex
- aseptate fungal hyphae: multinucleated, complex, large
Life processes
Metabolism: the web of all enzyme catalysed reactions in a cell
Response: the organism’s response to internal and external stimuli
Homeostasis: maintenance of a constant internal environment
Growth: a permanent increase in physical size due to an increase in cell size, cell number or both
Reproduction: the production of offspring from a parent organism
Excretion: the removal of the waste products of metabolism from the organism’s body
Nutrition: the consumption and use of nutrients for energy and growth
Paramecium life processes
M: enzyme catalysed reactions within the cytoplasm
R: moves using its cilia
H: osmoregulation. controls the cytoplasm’s osmolarity by collecting excess water in contractile vacuoles then expelling it through PM
G: grows by consuming organic molecules until it reaches critical ratio then divides asexually
R: sexual and asexual. asexual - 2 daughter cells via binary fission
E: waste products of respiration are removed through whole membrane surface
N: microorganisms/food particles are engulfed via feeding groove - digested and absorbed in cytoplasm
chlamydomonas life processes
M: enzyme catalysed reactions in the cytoplasm
R: uses eyespot to sense light changes -> move there for photosynthesis
H: osmoregulation. collect excess water in contractile vacuoles and expels it through PM
G: produce organic molecules till reach a critical ratio, then divide via binary fission
R: sexually or asexually
E: excretes using whole body surface (PM)
N: generates own organic molecules via photosynthesis using large chloroplast
Why do cells need to divide after reaching a certain size
- the rate of material exchange is a function of surface area
- the rate of metabolism is a function of volume
- unicellular organisms require a high SA:V -> molecules for life processes diffuse in and out of the cell through the PM
- as cell size increases the surface area to volume ratio decreases -> rate of material exchange compared to rate of metabolism isn’t enough to sustain life processes
- if the rate of metabolism exceeds the rate at which material is transported in and out of the cell, the cell will die
- excess heat not lost efficiently
- increased V = increased diffusion time, increased V = increased metabolism -> need more resources
- ## after a CRITICAL RATIO IS REACHED, cell divides (critical ratio stimulates mitosis)
Why do cells need to divide after reaching a certain size? [5]
- the rate of material exchange is a function of surface area
- the rate of metabolism is a function of volume
- as cell size increases the surface area to volume ratio decreases -> volume increases faster than surface area
- if the rate of metabolism exceeds the rate at which material is transported in and waste is transported out of the cell, the cell will die
- cell divides to ensure the SA:V is low
what are emergent properties [1]
when individual components interact to carry out specialised functions that the parts couldn’t carry out individually
Define cell differentiation [2]
Also, describe the packaging of DNA in the cells [1]
The expression of certain genes but not others in cells. The cells have specialised structure and functions as a result
- Active genes -> euchromatin -> expanded form -> accessible to transcriptional machinery
- Inactive genes -> heterochromatin -> condensed form -> saves space -> not accessible to transcriptional machinery
2 main qualities of stem cells that make them useful [2]
Types of stem cells [4]
- capable of self renewal
- can differentiate into any specialised cell
- Totipotent -> can differentiate into any cell type + extra-embryonic/placental tissue (eg - zygote)
- Pluripotent -> can differentiate into any cell type in an organism (eg ESCs)
- Multipotent -> can diff into certain types of similar cells (hematopoietic SCs)
- Unipotent -> can’t differentiate, but capable of self-renewal (eg - muscle stem cells)
Explain the use of HSCs for leukemia
- haematopoietic cells from bone marrow/peripheral/cord blood extracted
- damaged WBC in the body are killed via radio and chemo
- the HSCs are re-inserted into bone marrow where they differentiate –> healthy cells replaced
Explain the use of ESCs for Stargardt’s
- disease: macular degeneration of receptor cells in the retina –> loss of central vision
- ESCs treated to make retinal photoreceptor cells
- reinserted into the retina, attach and become functional
- central vision returns
Process of stem cell diff [3]
- treatment with biochemical solutions to trigger differentiation
- reinsertion into the patient
- suppression of host immune system if cells are foreign
- monitoring -> ensure not cancerous
Ethical/DA and A discussion of each type of SC (3 points per A/DA per type)
ESCs -
A: - can differentiate into almost any cell type
- many escs from IVF/abortions and things go waste anyway
- lower chance of genetic damage
- may provide relief to existing patients
- have been successfully used before
DA:
- lack of consent of ESCs -> are killed
- increased risk of rejection -> foreign
- increased risk of tumours
- religious/political groups may be against the whole killing the embryo vibe
- invasive surgery/potential exploitation (not the best point but in case)
ASC-
A: - adults can give informed consent
- involves no killing
- if sc from the patient, lowered rejection chance
- most adult tissues have some stem cells
DA: - smaller number of cell types it can differentiate into
- only certain/limited sources it can be derived from
- certain adult cells have no SCs
CBC:
A: - the umbilical blood is discarded anyway, so would go to waste otherwise
- little to no rejection chance
- infrastructure in place to store and collect it
- easy to obtain
DA:
- very little cord blood
- can’t differentiate into many cell types
4 kingdoms of eukaryotes
- Protista - unicellular/multicellular without specialised tissue
- fungi - cell wall of chitin -> obtain nutrients heterotrophically
- plantae - cell wall of cellulose, obtain nutrients autotrophically
- animalia - no cell wall, obtain nutrients via heterotrophic ingestion
organelles of cells
All cells:
- cytoplasm: fluid inside the cell containing all the organelles + where most metabolic rxns occur. jelly-like, mainly water + dissolved substances.
- cytoskeleton: inner scaffolding. provides structure and aids in material transport.
- centrioles + MT: c: anchor points for microtubules in processes. mt: small, cylindrical fibres -> moves chromosomes in cell division
- free ribo: synth polypeptides
(via translation fo mrna) for use in cell. has larger and smaller binding sites for tRNA and mRNA respectively
Eukaryotic
- rER: made of flattened sacs called cisternae + studded w ribosomes. synthesis of proteins for secretion
- sER: made of cisternae. lipid production
- golgi: flattened membrane sacs. processes, modifies and packages proteins for secretion.
- vesicle: single membrane org used to transport material in cell
- mitchon: has 2x-mem, inner foldings called cristae, matrix (enzymes) and mem proteins.
- PM: made of PBL w mem proteins. allows the entry of some materials but not others into the cell -> selectively permeable
- lysosome: contains enzymes. dogests damaged parts of the cell or the whole cell itself
- nucleus: double membrane structure with pores. has the genetic info of the cell. site of DNA replication, transcription and
Plant only:
- cell wall: made of cellulose,e rigid, high tensile strength, permeable -> to give structural support, ensure plant turgid, doesn’t lyse with excess water uptake
- chloro: 2x membrane structure, chlrorphyll, thylakoids, grana, stroma. site of photosynthesis.
- Vacuole: single cell membrane -> holds waste, fluids, excess water, nutrients. maintains hydrostatic pressure
define resolution
the smallest distance that can be clearly seen on an electron microscope
LM v EM
- LM shines visible light through sample, EM firing electrons at sample
- LM samples can be live, EM must be chemically treated
- EM has greater magnification (250,000x/LM has 2,000x) and resolution (1 nm/LM has 200 nm)
- LM: samples take a few minutes to prepare, EM can take hours
- LM: colour images, EM: black and white
SEM v TEM
SEM: high resolution image of the surface of a 3D object
TEM: High res image of a cross section of an object
Properties of the bilayer (acc to bioninja)
- Fluid -> as individual PL can move around within the layer -> hence can exo and endocytosis
- selectively permeable: some substances cannot pass through the hydrophilic or hypho layers
2 types of membrane protein and how they attach to membrane [2]
- Peripheral: temporary proteins, attach via non-covalent attractions to one surface of the membrane
- Integral: permanently attached, span across the membrane (associate with both surfaces)
