Miss Hodges Biology Module 2 Flashcards
Cell organelles, Specialised cells, Magnification, Mitosis and Meiosis, Membranes and Nucleic acids
What is a light microscope?
A microscope that uses visible light and a system of glass lenses to generate a magnified image of a specimen
What is magnification defined as?
The degree to which an image produced by a microscope is bigger than the actual specimen
How can staining a specimen help to provide better resolution in a microscope?
When some parts of the specimen are stained, some parts become darker than others, so absorb more light helping to provide contrast
What is the range of magnification where a light microscope is still useful?
x1500-x2000
What is resolution defined as?
minimum distance between two points at which those points can be observed as separate
What is the maximum resolution of a light microscope?
The light microscope can reach a resolution of 0.2 micro-meters or 200nm
What is a transmission electron microscope (TEM)?
An electron microscope that has the electrons passing through a thin section of a dead specimen, in a vacuum, and electromagnets, acting as lenses, focus and magnify the image.
What is the process of using a TEM?
- The microscope fires super-fast electrons through a super thin specimen
- The electrons are focused using condenser lenses (electromagnets)
- The electrons are scattered by the electrostatic potential of the specimen
- The scattered electrons then pass through the electromagnetic objective lenses
- Focuses electrons scattered from one area of the specimen to the same point on a photographic plate to form an electron micrograph
Why can’t we be sure that all objects on a TEM electron micrograph are actually there?
Because TEM micrographs can contain artefacts. This is damage to the cell caused during it’s preparation for the microscope
What is the max mag and res of a TEM?
Mag=x5,000,000 or more Res=0.2nm
What is a scanning electron microscope (SEM) ?
An electron microscope that has an electron beam that scans the surface of a specimen, exciting electrons, collecting them, and focusing them into a screen as a 3D image, in another vacuum.
What is an SEM used for?
Creating high resolution, high magnification 3D images of a surface, including all of the depth of the surface
What is the max mag and res of an SEM?
Mag=x1,000,000 maybe x2,000,000 Res=1-2nm
What are laser scanning (confocal) microscopes?
A microscope that uses a light laser to focus on a specific plane within the sample. It does this using a series of lenses and mirrors to focus the laser on a specific part of the specimen
What does a confocal microscope allow us to do?
It allows scientists to observe living cells in 3D, and allows us to see certain parts of cells, such as proteins moving around inside
What’s the max mag and res for a confocal microscope?
Mag=x2000, Res=200nm on xy plane, 500 on z plane
What is the nucleolus?
An area in the nucleus, usually seen as the darkest part of the nucleus, where the amount of DNA and Chromatin is densest.
What is Chromatin and what is its function?
Chromatin is a combination of DNA and histone proteins. The DNA is packaged in this way to make it more compact and allow it to fit inside the nucleus, as each DNA strand is very long
What is the membrane that surrounds the nucleus called?
The nuclear envelope. This is a phospholipid bi-layer that contains small nuclear pores that allows certain biological molecules like mRNA and ribosomes in and out the nucleus. The nucleus is therefore an example of a membrane bound cell organelle
What is the RER?
The rough endoplasmic reticulum is a system of fluid filled membranes called cisternae. The surface of the RER is covered in ribosomes and is used as an intra-cellular transport system, as the cisternae form channels which transport substances around the cell. It also provides a large surface area for the ribosomes to work on and then the proteins synthesised by the ribosomes travel through the cisternae, being folded into their tertiary structure, to the golgi app for packaging.
What is the SER?
Like the RER it is a system of fluid filled cisternae, but unlike the RER it doesn’t have ribosomes on its surface. It contains enzymes that catalyse lipid metabolism reaction like the synthesis of lipids and steroid alcohols.
What is the golgi apparatus?
A system of vesicles and folded membranes within the cytoplasm of most eukaryotic cells, involved in the secretion of proteins for inter-cellular purpose’s. Secretory vesicles that are “pinched off” from the main golgi apparatus carry these proteins to and from the golgi app. The proteins may also be modified whilst in the golgi app such as having another polypeptide chain added to create the proteins quaternary structure.
What are mitochondria?
They are a rod-shaped organelle responsible for the production of ATP during aerobic respiration. It consists of 2 membrane the outer mitochondrial membrane, that is lipid rich, and the inner mitochondrial membrane, which is protein rich. The IMM is folded into cristae, and holds the mitochondrial matrix.
What are chloroplasts?
They are plant organelles that are responsible for the production of carbohydrates from sunlight. It has an OM and an IM just like mitochondrion. The IM contains a fluid matrix called the stroma. It also contains thylakoids stacks called granum’s. Between granum’s there are structures that support the organelle called intergranal lamellae.
What are Lysosomes?
Small organelles filled with hydrolytic enzymes. They are present in phagocyte white blood cells to help digest pathogens.
What are cilia and undulipodia?
Protrusions from the cell surface membrane that contains microtubules from a centriole. They can detect signals about the environment surrounding the cell.
What are ribosomes?
They are made of rRNA, and are constructed in the nucleolus as two separate subunits, passing through the nuclear envelope before combining. They can either be free or on the RER. Those on the RER usually synthesise secretory proteins whereas free ribosomes usually synthesise intra-cellular proteins.
What is the cytoskeleton?
A microscopic network of protein filaments and tubules (made of tubulin subunits) in the cytoplasm of many living cells, giving them shape and coherence.
What is a cellulose/chitin cell wall?
A tough, inelastic covering that is not present in animal cells. It is made of bundles of cellulose/chitin polysaccharide chains.
What is the process that excretory proteins go through from creation to cell exit?
- DNA in the nucleolus is copied to create mRNA
- mRNA leaves the nucleus via the nuclear pores, attaching to a ribosome on the surface of the RER
- The ribosome reads the mRNA, synthesising the protein by joining together the required amino acids
- The assembled protein passes into the RER, folding into its tertiary structure and passed into a vesicle for transport to the golgi app
- Passed from the vesicle into the golgi app where it may be modified (quaternary structure, ….) and packaged into a vesicle for transport to the cell surface membrane
- Vesicle releases protein at plasma membrane, and either protein becomes part of the membrane itself or it performs exocytosis, releasing the protein into the body
How are prokaryotic and eukaryotic cells different?
Always:
-Prokaryotes do not centrioles and have a less developed cytoskeleton
-No nucleus or histone proteins, DNA is looped and free in cytoplasm
-No mitochondria, ER, chloroplasts or golgi app
-Contains non-linear chromosomes
Sometimes:
-Has a protective waxy capsule outside cell wall
-Has DNA loops called plasmids
-Has flagella
-Has pili, small projections on the outside of the cell that allow them to adhere to each other or a host, and pass plasmid DNA to pass between cells
How is prokaryotic DNA different from eukaryotic DNA?
The structure is the same but it is packaged differently. Generally there is only one DNA molecule, and so 1 chromosome, that is supercoiled so that it is compact. The genes are grouped into operons which allows them to be switched on or off.
How are prokaryotic ribosomes and eukaryotic ribosomes different?
They are smaller at 70S than the 80S eukaryotic ribosomes and are involved in the formation of smaller, less complex molecules.
What is the endosymbiotic theory?
Theory that eukaryotic organelles such as mitochondria and chloroplasts from ancient free living prokaryotes invaded primitive eukaryotic cells.
What is interphase?
The period in the cell cycle where the cell grows and the organelles duplicate, etc. It consists of growth phase 1 (G1), synthesis phase (S), and growth phase 2 (G2)
What happens in the G1 phase?
-The cell grows in size
-Gene transcription to create RNA
-Organelles duplicate
-Normal cell function, e.g. biosynthesis including the synthesis of enzymes needed in the S phase
What happens in the S phase?
-Chromosomes are unwound and everything is replicated
-When all chromosomes are replicated they should each contain a sister chromatid
-Active genes are replicated first, inactive last This is a rapid phase as the DNA bases are vulnerable to mutation. Once entering this phase the cell must complete the cell cycle.
What happens in the G2 phase?
-The cell grows (not as much as G1)
-Chemicals ensure the cell is ready for mitosis
-Stimulates proteins involved in condensing chromosomes and spindle fibre growth
What happens in the G0 phase?
-It is a resting place triggered by a checkpoint chemical at the end of G1
-In this phase cells may go through apoptosis (controlled cell death), senescence (cell becomes old and redundant but doesn’t die) or differentiation (neurones remain in this state indefinitely)
What is mitosis?
The division of the nucleus to create two genetically identical daughter nuclei. It is separated into 4 phases, PMAT: -Prophase -Metaphase -Anaphase -Telophase
What happens in prophase?
-The chromosomes, which now consist of 2 sister chromatids, shorten and thicken as the DNA supercoils
-The nuclear envelope disintegrates
-The centriole divides and moves to opposite poles of the cell
-Tubulin starts to form the spindle fibres between the daughter centrioles
What happens in metaphase?
-The pairs of chromatids line up at the equator of the cell
-They attach by the their centromeres to the spindle fibres
What happens in anaphase?
-The spindle fibres shorten, pulling, along with molecular motors, each sister chromatid in a pair to opposite poles
-Therefore the centromere of each pair splits
What happens in telophase?
-The separated chromosomes reach opposite poles
-A new nuclear envelope starts to form at both poles
-The cell now contains two sister nuclei that are genetically identical
What is cytokinesis?
The pulling in of the cytoskeleton to divide the cell in half and create 2 separate, functioning, identical daughter cells.
Why is meiosis described as reduction division?
It produces haploid cells to allow for sexual reproduction to create diploid cells.
What are somatic cells?
Diploid body cells not involved in sexual reproduction and containing 46 chromosomes.
What are germ cells?
Reproductive cells that give rise to sperm and ovum, containing 23 chromosomes.
What happens in meiosis I?
In meiosis I homologous chromosomes pair up, and each pair separates, producing two haploid cells with their sister chromatids still joined.
What happens in meiosis II?
Meiosis II is like mitosis; sister chromatids separate and four haploid cells are formed. Note that each has half the chromosomes of the parent cell. These cells differ genetically from each other and from the cells of the parents.
What is crossing over?
The rearrangement of genes between non-sister chromatids in a homologous pairs of chromosomes during the prophase I of meiosis. This can create lots of genetic variation amongst offspring from sexual reproduction.
What happens in prophase I?
-The chromosomes condense
-The nuclear envelope disintegrates
-The centriole divides and tubulin spindle fibres start forming between them
-Homologous chromosomes pair-up to form bivalents
-Crossing over occurs
What is independent assortment?
The random distribution of the bivalents and the direction that they are facing, which is independent to all the other bivalents.
What happens in metaphase I?
-Chromosomes move to the equator of the cell
-The chromosomes attach to the spindle fibres via their centromeres
-Independent assortment
What happens in anaphase I?
-The chromosomes in a homologous pairs are pulled to opposite poles of the cell
-The centromeres do not divide and each chromosome consists of 2 chromatids
-The crossed over areas separate resulting in swapped areas of chromosomes and allele shuffling
What happens in telophase I?
-A nuclear membrane forms around each cluster of chromosomes in most animal cells
-Cytokinesis occurs in animal cells, plant cells go from anaphase I to prophase II
-New nuclei are haploid, containing half the chromosomes of the parent cell
What happens in prophase II?
-New nuclear envelopes disintegrate
-Chromosomes supercoil
-Chromatids are no longer identical due to crossing over in prophase I
-New spindle fibres form at 90* to previous ones
What happens in metaphase II?
-Chromosomes line up at the equator
-Chromosomes attach to the spindle fibres via the centromere’s
-Independent assortment
What happens in anaphase II?
-Centromeres divide
-Chromatids move to the opposite poles of the cells
-Therefore the chromatids are randomly segregated
What happens in telophase II?
New nuclear envelopes forms around the haploid nuclei
How does meiosis create genetic variation?
-Recombination/Crossing over during prophase I
-Independent assortment of chromosomes in metaphase I and II
What is differentiation?
The process in which become specialised and certain genes are/are not expressed, usually in embryonic stem cells.
What are 4 types of specialised cells?
-Erythrocytes (red blood cells)
-Neutrophils (white blood cells)
-Spermatozoa (sperm cells)
-Squamous/Ciliated epithelial cells
How are erythrocytes specialised for their function?
-Carry O2 from the lungs to respiring cells
-Very small, about 7.5 μm in diameter
-Paired with biconcave disk shape allows large SA/V ratio and easier O diffusion
-They have a flexible cytoskeleton to fit down narrow capillaries
-They have almost no organelles to allow more space for haemoglobin, which is synthesised when the cell is immature and still has organelles
How are neutrophils specialised for their function?
-They travel to and engulf invading pathogens, before destryoing them
-They up to 2x the size of erythrocytes to allow them to swallow large pathogens
-Contain a multi-lobed (many part) nucleus
-Contain many lysosomes with hydrolytic (digestive) enzymes
How are spermatozoa specialised for their function?
-Contain many mitochondria to provide ATP and energy for the undulipodia
-Small, long and thin
-When egg reached enzymes released from acrosome (specialised lysosome) digesting protective outer layer
-Sperm head contains haploid gamete nucleus, but little else including little cytoplasm
How are squamous epithelial cells specialised for their function?
-Function to provide covering and thin walls for organs/alveoli
-Flattened shape
-Many have cilia or microvilli
-Cells bound with very tight junctions made of desmosome cells
What is epithelial tissue and how is it differentiated?
Epithelial tissue covers and lines surfaces in the body e.g., heart walls, blood vessels…
-Made of epithelial cells packed closely together in an almost continuous sheet
-Cells bound by tight junctions of desmosome cells
-The tissue contains no blood vessels relying on diffusion
-Many contain microvilli or cilia
-They have a short cell cycle of around 8 hrs to replace dead cells
-Its main functions are protection, absorption, filtration, excretion and secretion
What is connective tissue and how is it differentiated?
-Non-living extracellular matrix, consisting of carbohydrate polysaccharide chains like hyaluronic acid to trap water, and fibrous proteins such as elastin and collagen to keep structure
-The matrix separates the living cells within the tissue and enables it to withstand force such as weight
-Examples include blood, cartilage, ligaments and parts of skin
What is cartilage and how is it differentiated?
-It is a type of connective tissue and consists of elastic, fibrous and hyaline cartilage
-Immature cartilage cells are called chondroblasts
-Chondroblasts divide via mitosis and secrete the extracellular matrix
-Mature chondroblasts become chondrocytes and maintain the matrix
-Elastic cartilage examples = outer ear (pinna), epiglottis (larynx flap)
-Fibrous cartilage examples = disks between vertebrae, knee joint
-Hyaline cartilage examples = embryonic skeleton, covers ends of long bones, joins ribs to sternum, the nose, trachea rings and the larynx
What is muscle tissue and how is it differentiated?
-It contains lots of blood vessels to provide it with O2 for aerobic respiration and ATP production
-Muscle cells are called fibres, elongated and contain micro-filaments made of actin and myosin to allow contraction
-Can be skeletal, cardiac or smooth muscular tissue
-Skeletal-packaged by connective tissue sheets, joined to bones via tendons, when contracted cause bone movement
-Cardiac-makes up the hearts walls, when they contract allows the heart to beat and pump blood
-Smooth-occurs in intestine walls, blood vessels, uterus and urinary tract, and propels substances along these tracts
How are palisade cells specialised for their function?
-Long and cylindrical allowing them to pack closely together with small air spaces between them to allow easier gas diffusion
-Contains a large vacuole pushing the chloroplasts to the cell periphery to lower distance gas has to diffuse and to get maximum sunlight exposure
-Many chloroplasts
-Contain motor proteins on cytoskeleton to move chloroplasts to the area of sunlight on the leaf
How are guard cells specialised for their function?
-Found at bottom of leaf to reduce H2O loss, allow all palisade cells to be at the top of the leaf and to allow easy gas diffusion
-Contain chloroplasts to allow them detect sunlight/lack-of and open or close because of this
-Use ATP to create separate cell energy for active transport, which they use to maintain their low water potential, bringing solutes in, so that water can travel into the cell via osmosis and cause the cell to become turgid
How are root hair cell specialised for their function?
-Contain root like projections to increase SA
-No chloroplasts due to lack of sunlight
-Contain carrier proteins in plasma membrane for active transport of solutes through hydrophobic plasma membrane
-Produce ATP for active transport
-Contain large vacuole containing solutes to maintain the concentration gradient for active transport and the low water potential for osmosis
What is the vascular bundle?
It is a continuous tube up the plant stem that contains the xylem vessels, the phloem vessels and the cambium, and area between the vessels containing meristematic tissue which will differentiate into either phloem vessels or xylem vessels.
What is Meristematic tissue and how is it differentiated?
-Tissue containing pluripotent stem cells to differentiate into any type of plant tissue or cell
-Makes up the cambium
-Cells have a thin wall containing little cellulose, a large vacuole and no chloroplasts
What is a xylem tissue and how is it differentiated? (specialised tissues + transport in dicotyledonous plants)
-Long thin tube-like structure that carries water and dissolved solutes (minerals + ions) up the plant
-Helps provide structure to plant
-Lignified cells walls add strength to withstand the hydrostatic pressure so the vessels do not collapse, and make them impermeable to water
-No end plates allow mass flow of water as cohesive and adhesive forces not impeded
-No protoplasm (cytoplasm + nucleus) doesn’t impede mass flow through cell
-Bordered pits allow the lateral movement of water and allows the continual flow in case of air bubbles
-Small vessel diameter helps prevent H2O column breaking + capillary action
Made of 4 cells:
-Tracheids, long thin tapered cells with pits that help transport water
-Vessel elements, large with no end plates and lignified cell walls to transport water
-Xylem parenchyma + sclerenchyma, help provide support and are made of sclerieds and fibres
What is the phloem tissue and how is it differentiated? (specialised tissues + transport in dicotyledonous plants)
-A long tube like structure containing sieve-like structures in the stem to transport solutes/sugars (assimilates) UP and DOWN (bi-directional) the plant
-Cells from cambium either become companion cells or sieve tube cells
-Contains parenchyma for support
Sieve tube cells:
-lose most of their organelles (some ER and mitochondria) to maximise space for translocation
-sieve plates develop with sieve pores for continuous movement
-Cellulose cell wall helps withstand the hydrostatic pressure moving assimilates
-Thin cytoplasm reduces friction to facilitate movement
Companion cells:
-Keep organelles to provide support for sieve tube and unload/load assimilates
-Has lots mitochondria + carrier proteins to provide ATP for transportation assimilates in or out of cells
-Plasmodesmata (cell wall pores) to link sieve tube elements together to allow assimilate movement in and out
What is epidermal tissue and how is it differentiated?
-Consists of flattened cells with, no chloroplasts, for protection
-Some form waxy cuticle
-Equivalent to epithelial in animals
What are stem cells?
They are undifferentiated cells that have the potential to have all genes expressed or “switched off”, and so can usually become most types of tissue or cell.
What does stem cell potency refer to?
The varying ability of a stem cell to express or switch off certain genes, and its ability to differentiate into any type of cell/tissue.
What are the different potency’s of stem cells?
Totipotent:
-Embryonic stem cells that can differentiate into any intra-cellular tissue/cells
-They can create an entire organism, e.g., the first 16 zygote cells are totipotent stem cells
-Can create extra cellular structures, e.g., umbilical cord
Pluripotent:
-Embryonic stem cells that can differentiate into any intra cellular tissue/cells
Multipotent:
-Adult stem cells that can differentiate into a limited variety of tissue/cells
What are antigens?
Molecules, usually glycolipids and glycoproteins, on the outside of the cell membrane. They identify that the cell is native to the organism.
What are extrinsic and intrinsic proteins?
Extrinsic:
-Proteins that occur on the surface of the cell membrane, e.g. antigen molecules
Intrinsic:
-Proteins that span the length of the cell membrane, e.g. ion channels
What are ion channels?
Proteins that create a pathway for certain charged or water soluble molecules to pass through the phospholipid bi-layer. Some of these are gateway molecules that will open and close.
What are transport proteins?
Proteins transport usually large molecules to big to diffuse across the membrane through the phospholipid bi-layer. These are molecule specific so will only transport a specific atom/molecule across the membrane
How does cholesterol affect membrane fluidity?
-It acts as a fluid buffer
-This means that it, being amphipathic, attracts and binds to the hydrophobic phospholipid tails and pulls them together, causing the membrane to become more rigid
-Increases the mechanical strength of the membrane
What are glycolipids?
-Carbohydrates bonded to a lipid
-Sits within a plasma membrane with the carbohydrate polysaccharide being extrinsic to the membrane
-Can act as an antigen or a receptor
What glycoprotein?
-A carbohydrate bonded to an extrinsic protein
-Can act as receptors, inter-cellular signalling and sometimes as antigens
Why is the phospholipid bi-layer described using the fluid-mosaic model?
Fluid:
-Phospholipid molecules move independently to each other
-The membrane can flow and move
Mosaic:
-The membrane contains many proteins and molecules so, under a 2D microscope, looks like a mosaic
What is diffusion and why is it passive?
The movement of particles from an area of high concentration to an area of low concentration until an equilibrium is reached. This can be either simple or facilitated and is passive as no energy input for it to occur.
What is the process of simple diffusion?
A substance passes through a membrane without the aid of an membrane protein to allow it to pass through the membrane. A dynamic equilibrium will be reached. This diffusion will occur for hydrophobic and lipid soluble molecules.
What is facilitated diffusion?
It is the movement of molecules across a membrane with the aid of intrinsic proteins. These are either ion channels, channel-mediated diffusion, or carrier proteins, carrier-mediated diffusion.
Channel-mediated diffusion:
-Provides channels for ions to travel down a concentration gradient
-Water-filled so are hydrophilic
Carrier-mediated diffusion:
-Specific molecule binds to the protein
-Protein changes shape to release the molecule into the cytoplasm
How does alcohol affect membrane permeability?
Phospholipids are soluble in non-polar solvents, so large concentrations of alcohol molecules can result in the disruption and even dissolution of the membrane. The alcohol molecules push apart the phospholipid molecules in the bi-layer, disrupting the regular arrangement and causing fluidity, and therefore permeability, to increase.
How can temperature affect membrane permeability?
1) Phospholipids become more fluid when the kinetic energy of each phospholipid increases, to the point of overcoming the weak London forces between phospholipids to increase permeability.
2) Proteins in the membrane may move to a separate site, stopping chemical reactions. Proteins may also denature as hydrogen bonds in their tertiary structure are broken.
3) A decrease in temperature causes a decrease in both fluidity and therefore permeability, as the phospholipids lose kinetic energy, and so are pulled closer together.
How might an extremophile in cold conditions contain in their membrane to stop it from stiffening?
They will contain a higher ratio of unsaturated fatty acids to saturated fatty acids in their phospholipid molecules. This is because the kinks in the hydrocarbon chain push other phospholipids away, maintaining the fluidity of the membrane.
What is osmosis?
The net movement of water molecules from an area of high water potential to an area of low water potential across a partially permeable membrane, until a dynamic equilibrium.
What is water potential?
The concentration of free water molecules in a solution, ψ.
What does isotonic, hypotonic and hypertonic mean?
Isotonic: The water potential inside the cell and the solution surrounding the cell are equal so there will be no net movement of water molecules.
Hypotonic: The water potential of the cell is less than the water potential of the surrounding solution so water will move into the cell, in animal cells sometimes causing them to burst.
Hypertonic: The water potential of the cell is more than the water potential of the surrounding solution so water will move out of the cell into the solution, causing cells to shrink, which in plant cells results in the plasma membrane pulling away from the cell wall, described as plasmolysed.
What is the ψ of both pure water and a diluted solution?
Pure water = 0 ψ Diluted solution = always a negative ψ
What does ψs and ψp mean?
ψs = solute potential (concentration of solute) ψp = pressure potential (pressure of an enclosed fluid)
What is active transport, and some examples?
The movement of minerals or ions across a cell surface membrane, against a concentration gradient, via intrinsic carrier proteins. Some examples include:
-Sodium-potassium pumps, maintain ion concentrations for action potentials
-The absorption of minerals and ions in root hair cells
-The absorption of amino acids into the blood from the SI
-Endocytosis and exocytosis
What is ATP and ADP?
ATP = Adenosine Triphosphate ADP = Adenosine Diphosphate
What is the formula for active transport?
At carrier protein: ATP + H2O -> ADP + P
After active transport has occurred: ADP + P -> ATP + H2O
What are membrane pumps, and how do they work?
Membrane pumps are carrier proteins that allow molecules to move in and out of a cell
1. The molecule/ion being moved binds to the membrane pump
2. ATP is hydrolysed, forming ADP and an inorganic phosphate group, which then binds to the membrane pump
3. This causes the membrane pump to change shape and open on the other side of the membrane
4. The ion can then disassociate and is released on the other side of the membrane from where it started
5. The phosphate group then bonds to the ADP via condensation reaction to form ATP, allowing the membrane pump to return to its original shape
What is bulk transport?
The movement of extra-cellular fluid or material into the cell for use by the cell or to be ingested by lysosomes.
What are the 2 types of bulk transport?
Endocytosis is the bulk transport of material into the cell and is split into 3 processes, Phagocytosis, Pinocytosis and Receptor-mediated endocytosis
Exocytosis is the bulk transport of material out of a cell
What is the main process of endocytosis?
- The cell-surface membrane invaginates (folds inwards) forming a pocket around the material
- The pocket pinches off with help from specialised proteins
- Particles are now trapped in a newly formed vesicle inside the cytoplasm
- This can now be moved via molecular motor proteins along cytoskeleton threads into the cell interior
What is Phagocytosis?
- Means cell ‘eating’
- Takes in large particles such as cells or cellular debris are transported into the cell
- Phagocytosis is used by macrophages to ingest pathogens, during which the vesicle forms with a lysosome to digest it
What is Pinocytosis?
Cell absorbs small amounts of extra-cellular fluid and occurs continuously
Cell samples and resamples the surrounding fluid to absorb nutrients and is held in smaller vesicles than in phagocytosis
What is Receptor-mediated endocytosis?
-Receptor proteins capture a specific molecule and are extrinsic
-When bound to molecule, receptor triggers endocytosis
-Allows cells to absorb molecules in a low concentration, but can allow pathogens to enter
-Found in areas called ‘coated pits’
Why is ATP needed for bulk transport?
In this instance ATP is not needed for carrier proteins , but to help the plasma membrane invaginate and form a vesicle, and then for the molecular motors to move the vesicle along the cytoskeleton threads.
What is Exocytosis?
-Used to release material, eg waste products, into the extra-cellular fluid
-Vesicles, sometimes from golgi app, fuse with the cell-surface membrane and release their contents into the extra-cellular space
-Some become part of the membrane, while others follow the ‘kiss and run’ model, fusing just long enough to release contents before pinching off
What is a nucleotide made up of?
-A phosphate group bonded to a pentose sugar (deoxyribose in DNA and ribose in RNA)
-A nitrogenous base bonded to the pentose sugar
What are the 5 different nitrogenous bases and what molecule do they appear in?
- Adenine: Consists of 2 carbon rings bonded together, found in both DNA and RNA
- Thymine: Consists of 1 carbon ring and is found in only DNA
- Guanine: Consists of 2 carbon rings bonded together, found in both DNA and RNA
- Cytosine: Consists of 1 carbon ring and is found in both DNA and RNA
- Uracil: Consists of 1 carbon ring and is found only in RNA as a replacement for thymine
What nitrogenous bases form hydrogen bonds between each other?
Tiger Are Good Cats
Thymine - Adenine
Guanine - Cytosine
What is the structure of a molecule of DNA?
-It is a polymer molecule formed by the joining together of monomer nucleotide units via phosphodiester bonds
-Hydrogen bonds form between complementary bases on each DNA strand, 2 between T and A, and 3 between G and C
-The DNA strands are antiparallel, meaning that the strands point in opposite directions
How are nucleotides joined together?
The monomer nucleotides are joined together by phosphodiester bonds formed via a condensation reaction between the phosphate group on C5 of one nucleotide and the hydroxyl group on C3 of a different nucleotide molecule.
What are the purines and the pyrimidines?
Purines (2 ringed) = Guanine, Adenine
Pyrimidines (1 ringed) = Cytosine, Thymine, Uracil
How does an activated nucleotide differ from a regular nucleotide?
It contains three phosphate groups instead of the one, allowing 2 to hydrolyse off and form phosphodiester bonds with other nucleotide molecules.
What does ‘ mean in DNA?
’ means prime and indicates whether or not the DNA strand ends and starts with the hydroxyl group on C3 (3’) or the phosphate group on C5 (5’).
What enzymes are involved in semi-conservative DNA replication?
- Helicase - unzips and unwinds the DNA strands by breaking the hydrogen bonds
- Primase - initiates the process by adding RNA primers to the start and end of the DNA strands, allowing DNA polymerase to catalyse the replication
- Exonuclease - ends the process by removing RNA primers from DNA strand
- DNA polymerase - Catalyses the joining of complementary base pairing and the formation of the sugar-phosphate backbone
What are the steps of leading strand semi-conservative DNA replication?
- The double helix is unwound and unzipped by a helicase enzyme, forming a replication fork (area of replication)
- Free activated nucleotides bond to complementary bases on the template strand (A-T, G-C)
- DNA polymerase enzyme then catalyses the bonding of the bases and the forming of the phosphodiester bonds between nucleotides in the 5’ to 3’ direction
- These bonds form when 2 phosphate groups on activated nucleotides are hydrolysed, to be used again, releasing energy to form the bonds/Leading strand
Note: Leading strand is replicated continuously
What the 3 previous theories about DNA replication and how were they disproved/proven?
- Semi-conservative:
DNA molecule contains 1 old and 1 new strand of DNA - Conservative:
Complete parent DNA acts as a template for the new DNA molecule - Dispersive:
Old DNA split into fragments and copied before being joined together with the new parts so that every new molecule contains part of the old
Meselson experiment:
-E-coli grown in N^15, then switched to N^14 after 15 generations
-After switch, 1st gen put into a centrifuge and separated
-Weight was not 1/2 heavy, 1/2 light but all had a medium weight, so not conservative
-After 2nd gen, used centrifuge and found weight either medium or light, so not dispersive as in some DNA N^15 wasn’t present, so semi-conservative correct
What conditions are required for semi-conservative replication to occur?
- Free activated nucleotides must be present
- Both DNA strands being copied must act as a template
- Enzymes must be present: Helicase, Primase and DNA polymerase
- ATP is required to drive the process
What is the triplet code described as?
-Degenerate, there are more combinations of triplet base codes/codons than there are amino acids, so therefore each amino acid is coded for by a number of different codons.
-Universal, in almost all living organisms, the triplet code for each codon, and therefore for each amino acid is exactly the same.
-Non-overlapping, triplet code is read from a fixed point in groups of 3 bases, so there is no overlap of bases between codons, eg, ATG, GCA not ATGCA
What is transcription and its process?
-The mRNA copy of the DNA being made for protein formation
1. Helicase unzips a specific gene, breaking hydrogen bonds between comp bases
2. RNA polymerase moves along one strand of DNA (template strand) matching up free complementary activated RNA nucleotides
3. RNA nucleotides join together (releasing energy) via phosphodiester bonds
4. Newly formed mRNA molecule and template DNA strand split
5. DNA joins back together in double helix
6. RNA polymerase reaches ‘stop’ codon, and mRNA detaches and leave nucleus via nuclear pores
-1 template strand exposed and used to form complementary mRNA strand
-1 coding strand, identical (except T for U) to the mRNA strand
What is translation, and what is the process?
-The process through which a replicated strand of mRNA is turned into a polypeptide
1. A tRNA molecule, attracted to the ribosome, with a complementary anti-codon to the mRNA codon attaches via hydrogen bonds, with the tRNA being attached to a specific aa
2. mRNA can bond, via hydrogen bonds, to any 2 tRNA molecules at one time
3. Enzymes and ATP are used to join the aa with a peptide bond
4. 1st tRNA molecule is released, by the ribosome, to collect another aa of the same type
5. The process is repeated until a stop codon is reached and the polypeptide is released into the cytoplasm
What is tRNA (transfer RNA)?
-Transports a specific aa from the cytoplasm to the ribosomes
-Contains an anti-codon, complementary sequence of 3 nitrogenous bases to the codon for the aa it is transferring
-aa bonds to the 3’ end of the tRNA molecule
-Roughly 80 nucleotides long and folded into a clover shape
What is ATP and its structure? (+ how does it release energy, etc)
ATP stands for Adenosine (not adenine) Tri-Phosphate, a biological molecule that is to release energy in the body. It consists of:
-A ribose sugar
-An adenine nitrogenous base
-3 phosphate groups
This gives it a structure akin to that of an activated RNA nucleotide. It holds small pockets of energy for short tasks. The bonds between the 3 phosphates are also weak, meaning they are easily hydrolysed off, releasing energy, and meaning that only 1 reaction is needed to release energy, compared to the many for glucose.
What enzymes catalyse this release of energy, and what are the reactions?
Hydrolysis:
-Catalysed by ATP hydrolase
-Energy stored in Pi-Pi bond is released
ATP + H2O -> ADP + Pi
Condensation:
-Synthesis of ATP called Phosphorylation reaction, the synthesis of ATP via the addition of a Pi to an ADP molecule through a condensation reaction
-Allows molecule to be reused
-ATP synthase catalyses condensation ATP
ADP + Pi -> ATP + H2O
Why is ATP needed and produced in such large amounts?
-Holds temporary, short-term energy
ATP needed for:
-Metabolic processes such as macromolecule building, eg, polypeptides
-Movement as it’s needed to allow muscle fibre contraction
-Active transport as it changes the shape of carrier proteins in plasma membranes to allow molecule movement against gradient
-Secretion, eg, formation of lysosomes
-Activation of molecules, as inorganic phosphate can phosphorylate compounds to make them more reactive by lowering activation energy
Note: Approx. yield ATP from 1 glucose = 38
