1 Cell Biology Flashcards
What are the three points of cell theory?
- All living things are composed of cells
- The cell is the smallest unit of life
- Cells only arise from pre-existing cells
How do striated muscle fibres not conform to cell theory?
The muscle cells fuse to become very long and thus have multiple nuclei with only one plasma membrane
What part of cell theory do striated muscle fibres challenge?
That cells always function as autonomous units
How do aseptate fungal hyphae not conform to cell theory?
They do not have hyphae separating cells.
What part of cell theory do aseptate fungal hyphae challenge?
That cells are composed on discrete cells
How do giant algae not conform to cell theory?
They grow extremely large (7cm)
What part of cell theory do giant algae challenge?
That larger organisms are made up of many microscopic cells
What are the 7 basic functions integral to life?
Metabolism Reproduction Sensitivity Homeostasis Excretion Nutrition
How does paramecium fulfil the basic function of responsiveness?
They are surrounded by cilia which help them move
How does paramecium fulfil the basic function of nutrition?
They engulf food via a feeding groves called cytostome
How does paramecium fulfil the basic function of metabolism?
Food particles are enclosed within small vacuoles that contain enzymes for digestion
How does paramecium fulfil the basic function of excretion?
Solid wastes are removed via contractile vacuoles
How does paramecium fulfil the basic function of homeostasis?
Essential gasses enter and exit via diffusion
How does paramecium fulfil the basic function of reproduction?
They divide asexually but horizontal gene transfer can occur via conjugation
How do you calculate rate of metabolism?
Mass/Volume
Larger cells need more energy to sustain essential functions
What does a large surface area mean in terms of rate of material exchange?
More material movement
Equation for magnification
Magnification = (image size/ actual size)
What 3 things should be included in a good diagram of microscopic structires?
Title
Scale/ Magnification
Clear labels of only what was visible
Define a tissue
Collection of similar cells
Define an organ
Tissues working together to complete a function
Define organ system
Organs working together to complete a vital part of life
Define an organism
Group of organ systems and tissues working together to form one living unit
Define differentiation
The process during development whereby newly formed cells become more specialised
What happens genetically when cells are specialised?
Different parts of the genome are activated
How is DNA present in a eukaryotic cell?
In the nucleus and packed with proteins to form chromatin
Define and describe euchromatin
Where the active genes are usually packaged in an expanded way so that they can be easily read
Define and describe heterochromatin
Where the inactive genes are usually packaged in a condensed way (this saves space as they are not transcribed)
What are the two key qualities of stem cells?
Self Renewal
Potency
Define a Totipotent cell
Can form any cell as well as extra-embryonic (placental) tissue (e.g.: zygotes)
Define a unipotent cell
Can not differentiate but are capable of self-renewal
Define a multipotent cell
Can differentiate into a number of closely related cells
Define a pluripotent cell
Can form (almost) any cell type
What does the process of using stem cells require?
Biochemical solutions to trigger differentiation
Surgical implantation
Suppression of host immune system
Careful monitoring to ensure they do not become cancerous
What is Stargardt’s disease?
A disease caused by a gene mutation which leads to blindness
How can we treat Stargardt’s Disease?
Replacing dead retinal cells with functioning ones derived from stem cells
What is Parkinson’s Disease?
A disorder which effects dopamine-secreting nerve cells meaning a patient can no longer control smooth, purposeful movements
How can we treat Parkinson’s Disease?
Replacing dead nerve cells with functioning ones derived from stem cells
How can we treat Leukaemia?
Produce bone marrow from stem cells
How can we treat Paraplegia?
Repair damage caused by spinal injuries to enable paralysed victims to regain movement (by using tissue derived from stem cells)
How can we treat Diabetes?
Replace non-functioning islet cells with those able to produce insulin (derived from stem cells)
How can we treat burn victims?
Graft new skin to replace the damage using stem cells
What are the three sources to find animal stem cells?
Embryos
Umbilical cord blood or placenta of a new-born baby
Certain adult tissues (such as bone marrow - not pluripotent)
What are the two techniques for artificial stem cells?
SCNT (Somatic cell nuclear transfer)
Nuclear reprogramming
Describe somatic cell nuclear transfer (SCNT)
Involves the creation of embryonic clones by fusing a diploid nucleus with an egg cell (therapeutic cloning)
Describe nuclear reprogramming
Inducing a change in gene expression to transdifferentiate a cell
What is one of the negative side effects of nuclear reprogramming?
Involves the use of oncogenic retroviruses and transgenes increasing health risks
Which kingdom do prokaryotic cells fall into?
Monera
What are the two domains within monera?
Archaebacteria (such as extremophiles)
Eubacteria
Name the 10 cellular components of prokaryotic cells
Cytoplasm Nucleoid region Plasmids Ribosomes (70S) Cytoskeleton Cell membrane Cell wall Slime capsule Flagella Pili
What is the function of the slime capsule?
A thick polysaccharide layer used for protection against desiccation (drying out) and phagocytosis
What is the function of pili?
Adherence to surfaces or to mediate bacterial conjugation (sex)
What is the cell wall of a prokaryotic cell made of?
Peptidoglycan
Describe the process of binary fission
DNA replicates
Two DNA loops attach to the membrane
The membrane elongates and pinches off (cytokinesis)
Into which kingdoms can eukaryotes be divided?
Protista
Fungi
Plantae
Animalia
What are protista?
Unicellular or multicellular organisms without specialised tissues
What is the difference between 70S and 80S ribosomes and where can they be found?
70S is smaller than 80S
70S can be found in prokaryotes and mitochondria
80S can be found in eukaryotic cells
Describe the smooth endoplasmic reticulum
A bare membrane network with the function of lipid synthesis
Describe the rough endoplasmic reticulum
A membrane network studded with ribosomes with the function of protein synthesis of dangerous proteins
Describe the Golgi apparatus
An assembly of folded vesicles and membranes involved in sorting, storing, modifying and exporting of secretory products
Describe mitochondrion
Double membrane structure, site of aerobic respiration
Describe peroxisomes
Membranous sac containing enzymes, catalyses breakdown of toxic substances
Describe centrosomes
Microtubule organising centre, radiating microtubules from spindle fibres to contribute to cell division (paired in animal but not plant cells)
Describe chloroplasts
[PLANT]
Double membrane structure with internal stacks of membranous discs, site of photosynthesis
Describe the vacuole
[PLANT]
Fluid-filled cavity surrounded by membrane, maintain hydrostatic pressure
Describe the cell wall of eukaryotic cells
[PLANT]
External outer covering made of cellulose, provides support and prevents excess water uptake
Describe lysosomes
[ANIMAL]
Membranous sacs filled with hydrolytic enzymes, breakdown/ hydrolysis of macromolecules
What is the function of a transmission electron microscope (TEM)?
Generating high-resolution cross-sections of objects
What is the function of a scanning electron microscope (SEM)?
Display enhanced depth to map the surface of object in 3D
Disadvantage of electron microscopes
Cannot display living specimens in natural colours
Advantages of electron microscopes
Higher range of magnification
Higher resolution
Define a micrograph
A photo or digital image taken through a microscope
Why do phospholipids form bilayers in water?
Due to the amphipathic properties of their molecules
Define amphipathic
Having both hydrophilic and hydrophobic parts
Which part of the phospholipid is hydrophobic?
The two non-polar lipid tails
Which part of the phospholipid is hydrophilic?
The polar glycerol and phosphate head
How is the phospholipid bilayer flexible?
Individual phospholipids can move around within it
Why is fluidity important for the membrane?
Allows for spontaneous breaking and reforming of membranes (endo/exocytosis)
What types of proteins can be found within the phospholipid bilayer?
Integral proteins
Peripheral proteins
Describe integral proteins
Proteins which are permanently attached to the membrane and are typically transmembrane (span across the bilayer)
Describe peripheral proteins
Proteins temporarily attached by non-covalent interactions and associate with one surface of the membrane
Describe a channel protein
The non-polar (hydrophobic) amino acids associate directly with the lipid bilayer and the polar amino acids are located internally and face aqueous solutions
What tertiary structures do transmembrane proteins most commonly form?
Single helices
Helical bundles
Beta barrels
Which tertiary structure is most common amongst channel proteins?
Beta barrels
Describe an α-helix tertiary structure
Single helix
A single protein goes straight through the membrane, perpendicular to it
What are usually the functions of proteins in an α-helix structure?
Recognition
Receptors
Describe a helical bundle tertiary structure
Many proteins which cross straight through the membrane, perpendicular to it and are all connected
What are usually the functions of proteins in an helical bundle structure?
Enzymes
Transporters
Receptors
Describe a β-barrel tertiary structure
A tandem repeats that twists and coils through the membrane so that the first strand is bonded to the last
What are usually the functions of proteins in a β-barrel structure?
Transporters (channel proteins)
What are the functions of membrane proteins?
Junction Enzymes Transport Recognition Anchorage Transduction (receptors for peptide hormones) [Mnemonic JETRAT]
What is the function of cholesterol within animal cell membranes?
Maintaining integrity and stability
Why do plant cells not require cholesterol?
They already have a rigid cell wall
Describe cholesterol and it’s polarity
cholesterol is amphipathic
The cholesterol’s hydroxyl (-OH) groups is hydrophilic, the remainder, a steroid ring and hydrocarbon tail, is hydrophobic
How do the cholesterol molecules align within the membrane?
The hydrophilic hydroxyl (-OH) group aligns with the phospholipid heads, and the hydrophobic steroid ring and hydrocarbons align with the phospholipid tails
What are the main differences between the Davson-Danielli and the Singer-Nicolson Model?
There are transmembrane proteins in the Singer-Nicolson model
The membrane proteins moved and were not static in the Singer-Nicolson model
What is the widely accepted membrane model?
Fluid-Mosaic model
What were the assumptions and inaccuracies the Davson-Danielli model made?
All membranes were of uniform thickness
All membranes had symmetrical internal and external faces
Did not account for permeability
The temperatures at which the membranes solidified did not correlate
How were modifications made to the pervious model to change it to the fluid-mosaic model?
Fluorescent antibody tagging showed that proteins were mobile
Freeze fracturing found a rough surface providing proof for transmembrane proteins
Describe the permeability of a cellular membrane
(Selectively) semi-permeable
What are the three forms of passive transport?
Simple diffusion
Osmosis
Facilitated diffusion
Describe simple diffusion
Movement of small or lipophilic molecules down the concentration gradient
Describe osmosis
Movement of water molecules down the concentration gradient (from low to high concentration of sugars)
Describe facilitated diffusion
Movement of large or charged molecules via membrane proteins
How does active transport occur?
Through the hydrolysis of ATP into ADP and a phosphate group, the phosphate group then binds to a protein which will change shape to accommodate active transport
What are the two types of active transport?
Primary (direct) active transport
Secondary (indirect) active transport
Describe direct active trasnsport
Involves direct use of metabolic energy, can be split into uniport and cotransport. This is pump-mediated
Describe indirect active transport
Involves coupling the molecule with another along an electrochemical gradient, can be split into antiport and symport. This is carrier-mediated
Describe uniport (active transport)
When one molecule moves from low to high concentration
Describe cotransport (active transport)
When two molecules move across the membrane from low to high concentration simultaneously
Describe antiport (active transport)
When two molecules move in opposite directions across the gradient but the high and low concentrations for each are on the same side (therefore one is going with and another against the concentration gradient)
Describe symport (active transport)
When two molecules move together across the membrane in the same direction but one moves with and one against the gradient
When does simple diffusion stop?
When an equilibrium is reached
Which factors effecting rate of diffusion?
Temperature
Molecular size
Steepness of gradient
Describe a hypertonic solution
One with a high solute concentration
Describe a hypotonic solution
One with a low solute concentration
Describe an isotonic solution
Same solute concentration
What do we call a plant cell in a hypertonic solutions?
Shrivelled
What do we call a plant cell in a hypotonic solutions?
Lysed
What do we call a plant cell in an isotonic solutions?
Normal
What do we call an animal cell in a hypertonic solutions?
Plasmolysed
What do we call an animal cell in a hypotonic solutions?
Turgid
What do we call an animal cell in an isotonic solutions?
Flaccid
Which two types of proteins are involved in facllitated diffusion?
Carrier and channel proteins
Describe carrier proteins
Integral glycoproteins
How do carrier proteins work?
They bind to a solute and undergo a conformational change (they are also used in active transport)
What is the rate of transport of carrier proteins?
~1000 molecules/sec
Describe channel proteins
Integral lipoproteins which contain a pore via which ions may cross from one side of the membrane to the other
How do channel proteins work?
They use ions to regulate the passage of ions
How does the rate of transfer of channel proteins vary from that of carrier proteins?
Channel proteins have a much faster rate of transport than carrier proteins
What does a sodium-potassium pump do at rest?
Expels sodium ions from the nerve cell while potassium ions accumulate within
What happens in a sodium-potassium pump when the neuron fires?
The ions swap locations via facilitated diffusion via sodium and potassium channels
Define abiogenesis
The theory that living cells arose from non-living matter
What were the 4 stages of abiogenesis?
There was non-living synthesis of simple organic molecules
These molecules became more complex polymers
Some formed the ability to self-replicate
These were packaged into membranes
Which experiment demonstrated the theory of abiogenesis?
Miller-Urey
Describe the Miller-Urey experiment
A reducing atmosphere similar to that of early Earth was created
The mixture was then exposed to electrical discharge and left to cool for a week
This was then found to contain trace of simple organic molecules
To whom is the law of biogenesis attributed?
Louis Pasteur
Describe biogenesis
The principle that all living things arise form other living things by reproduction
How did Pasteur prove biogenesis?
Swan neck experiment
Describe the swan neck experiment
Two nutrient broths were sterilised. One had a swan neck the other was simply open.
After a week, microorganisms were only present in the open flask and not the swan neck flask, disproving miasma.
Define endosymbiont
A cell which lives inside another with mutual benefits
How did eukaryotes evolve?
From prokaryotic cells that were engulfed by phagocytosis and remained undigested as they contributed new functionality to the cell
Name two organelles believed to have formed from endosymbiosis
Mitochondria
Chloroplasts
Give evidence for endosymbiosis
Membranes (double membrane bound) Antibiotics (susceptibility) Division (mode of replication) DNA (presence and structure) Ribosome (size) [MNEOMONIC MAD DR]
Which are the two main phases of the cell cycle?
Interphase and the M phase
What are the stages of interphase?
G1, S and G2
What happens during G1 (interphase)?
Cell grows and prepares for DNA replication
What happens during S (interphase)?
Synthesis of DNA (DNA is replicated)
What happens during G2 (interphase)?
Cell finishes growing and prepares for cell division
What is interphase?
The part of the cell cycle where metabolism and growth occur.
(Consists of G1, S and G2 phases)
What is M phase?
The period in the cell cycle in which the cell divides into two daughter cells.
(Consists of mitosis and cytokinesis)
What are the stages of mitosis, in order?
Prophase Metaphase Anaphase Telophase Cytokinesis
Which are the key processes in mitosis?
DNA replication Organelle duplication Cell growth Transcription (key proteins and enzymes are synthesised) Obtain nutrients Respiration [MNEMONIC DOCTOR]
How is DNA found in the nucleus?
Usually loosely packed, unravelled chromatin
What is a chromosome?
The tightly wound and condensed form of DNA found prior to division
What is the difference between chromatin and chromosomes?
Chromatin is the loose DNA found during interphase which then undergoes supercoiling into a chromosome for cell division
What is either half of a chromosome calles?
Chromatids
What do we call the region where the chromatids are joined?
Centromere
What do we call replicated chromatids?
Sister chromatids
What do we call chromatids after division?
Daughter chromatids
Describe mitosis
The process of nuclear division whereby duplicated DNA molecules are arranged into two separate nuclei
Describe a cell just before mitosis
DNA is present as uncondensed chromatin (not visible under a microscope)
It is confined within a clearly defined nucleus
The cell is enlarged and ready to divide
Describe prophase
DNA supercoils and condenses
Paired centrosomes move to the opposite poles of the cell and form microtubule spindle fibres
Nuclear membrane breaks down and dissolves
Describe metaphase
Microtubule spindle fibres from both centrosomes connect to the cell centromeres
These contract aligning the chromosomes on the equatorial plate.
How do spindle fibres contract?
Depolymerisation
Describe anaphase
The contracting spindle fibres pull the chromatids to either pole (they are now chromosomes in their own right)
Describe telophase
The spindle fibres dissolve and chromosomes decondense
A new nuclear envelope forms
Describe cytokinesis in animal cells
The microtubules form concentric rings around the centre of the cell after anaphase
These constrict to form a cleavage furrow
When the furrow meets in the middle the cells pinch off
How is cytokinesis in animal cells described?
Centripetal - it occurs from the outside in
Describe cytokinesis in plant cells
After anaphase vesicles rich in carbohydrates form a row at the centre of the cell and fuse forming an early cell plate
This extends outwards to fuse with the cell wall forming two identical daughter cells
How is cytokinesis in plant cells described?
centrifugal - it originates at the centre and moves laterally
Define mitotic index
A measure of the status of a cell population (in terms of which cells are undergoing mitosis)
How do you calculate the mitotic index?
Ratio between number of cells in mitosis and total number of cells
How is the cell cycle controlled?
By cyclins (regulatory proteins)
Define phosphorylation
The attachment of a phosphoryl group
How do cyclins control the cell cycle?
Through the activation of CDKs which control the processes through phosphorylation
When a cyclin and CDK bond, they bind to a target protein and modify it via phosphorylation
What happens to the cyclin and CDK after phosphorylation?
The cyclin is degraded
The CDK is rendered inactive again
What does CDK stand for?
Cyclin dependant kinases
Define tumour
Abnormal cell growth resulting in uncontrolled cell division
What is a cancer?
A disease caused by the growth of tumours
Define mutagen
An agent that changes the genetic material of an organism
What are the three types of mutagens?
Physical (e.g.: radiation)
Chemical (e.g.: arsenic)
Biological (e.g.: bacteria)
Define oncogenes
A gene with the potential to cause cancer
Mutations to which two genes are most likely to cause cancer?
Proto-oncogenes (stimulate the cell-cycle)
Tumour suppressor genes (repress the cell-cycle)
Define mestastasis
When a cancer spreads from a primary location to a secondary location (becoming malignant)
What do we call a cancer that does not metastasis?
Benign
How many chemicals are there in cigarettes and how many ae carinogenic?
60 of 4,000 are carcinogenic
What percentage of lung cancer is attributed to smoking?
~90%
Define Mesosome
The part of a prokaryotic cell wall which folds inwards
