Flashcards in The Patient - Sem1 Deck (59):
Describe the timeline of life origins on Earth
- Prokaryotes were first cells (3.7bil years before humans)
- Eukaryotic were first cells with a nucleus (2.5bil years before humans)
- Oxygen atmosphere formed 1.5-2bil years before humans
- Multicellular organisms
What is the Cell Theory?
- All living things made of cells
- Cells formed from existing cells
- Organisms may consist of one or many cells
How was the Cell Theory proved?
- Louis Pasteur
- Broth in curved neck flask - No microorganism growth exhibited as no cells come into contact with broth
- Curved neck removed - Microorganisms can enter and grow through cell division
What are the basic features of all cells?
M - Always a selective outer MEMBRANE present, inner membranes may also be present
N - Genetic material is made of NUCLEIC ACIDS, inherited from parent cell or moved between cells
M - METABOLISM includes all the processes that occur in a cell that are critical to its survival
M - MOTILITY of the cell or it's individual components is key to its survival and metabolism
What are the key difference between prokaryotes and eukaryotes?
- SIZE: E. 10-100mcm, P. 1-5mcm
- Prokaryotes have no nucleus/membrane bound organelles/cytoskeleton
- METABOLISM: E. respiration or photosynthesis, P. varied metabolism
- CHROMOSOMES: E. many, linear chromosomes, P. single, circular chromosome
- Cell wall present in most prokaryotes but only plant and fungi eukaryotes
- E. generally multicellular, P. usually unicellular
- P. move using simple flagella, E. have complex microtubule flagella
- P. smaller ribosomes
- E. Cell division by mitosis/meiosis, P. division by binary fission
How do the size and shape of cells vary?
- Max. size dependent on SA:V ratio, big ratio causes problems with material exchange
- Cell needs to be big enough to carry out all metabolic functions
- Cell size varies from about 1mcm-1mm
- Organelle size varies from 1-10mcm
- Shape of cell may vary depending on function
Why do drugs have to cross a number of membranes in the body?
- Drugs enter bloodstream to reach target tissues (unless used topically)
- Unless injected drugs must cross many epithelial membranes to reach bloodstream and then target tissues
- May have to cross cell membrane if action is in cell
What are the common features of a typical membrane, and what is its arrangement?
- "Sheet-like" boundaries
- Lipid bilayers spontaneously formed
- Fluid - Dependent on saturation of fatty acids (C=C)
- Specific proteins in membrane determine function
- 6-10nm thick
Describe the structure of phospholipids
- Lipid + phosphate group
- Glycerol or sphingosine backbones
- Phosphoglycerides - fatty acid tails and phosphate+alcohol head attached to glycerol backbone
Describe the structure and function of fatty acids
- Straight carboxylic acid chains
- Unsaturated chains causes membrane fluidity (not packed together as closely)
- Can be stored as triglycerides and then used to produce ATP
- Can be used to make a specific target molecule
- Intracellar messengers (Eicosanoid family) - Oxygenated 20C f. acids
Describe the structure of glycolipids
- Lipid + sugar group
- Sphingosine backbone, one fatty acid and one or more sugar groups
- Fatty acid bonded to NH3+ group and sugar usually bonded to hydroxyl group
Describe the structure and function of cholesterol
- Sterol (Steroid Alcohol) - Polar -OH group and hydrophobic rings/chains
- Only found in animal cell membranes - regulate membrane fluidity bit fitting between f. acid molecules
- Prevents transition of fatty acids from gel to fluid
Why do lipid bilayers form spontaneously?
- Amphipathic molecules (phospholipids)
- In aqueous conditions bilayer forms to exclude water from hydrophobic region
- Liposomes can form from bilayers
- Bilayers are more energetically favoured than monolayers
What is the relationship between the permeability coefficient and the ability to traverse lipid bilayers?
- Coefficient represents solubility in organic solvents compared to solubility in water
- Bigger coefficient = more easily passes bilayer
How does the protein:lipid content in membranes vary?
- Varies depending on function of membrane
- If a lot of transport is required (e.g. liver) protein content may be high
- If membrane has an insulation function protein content may be low
What are integral proteins?
- Embedded in the membrane, usually span the entire membrane
- Usually alpha-helical structures
What are peripheral proteins?
- Loosely associated with membranes
- Cytosolic or extracellular
How are membranes synthesised?
- Growth of existing membranes
What is an animal cell glycocalyx?
- Layer of carbohydrates on extracellular surface
- May be attached
- Stained with ruthenium red
- Functions: cellular recognition and adhesion, disease development (pathogenesis)
- Made glycolipids and proteins and proteoglycans
- Membrane sugars are involved in cellular communication
Give an example of a drug that blocks membrane transport
- Digitalis (from foxglove leaves)
- Treatment of heart disease
- Prevents ion transport across membranes of cardiac muscle cells
Give an example of a disease where MDR transporters cause drug resistance to develop
- Cancer - over expressions of MDRs causes removal of anti-cancer drugs. Causes resistance to a number of drugs at the same time
- Malaria - Parasites resistant to anti malarial due to expression of MDRs
What are multi drug transporters?
- Pump a number of drugs out of cells, reducing their efficacy
What is endocytosis?
- Large molecules moved into cell by vesicles
- Pinocytosis - bulk transport of liquids into the cell
- Phagocytosis - bulk transport of solids into the cell
What is exocytosis?
- Movement of large molecules out of the cell using vesicles
- Constitutive = continuous movement
- Regulated = movement triggered by receptors
What is simple diffusion?
- The movement of small molecules down a concentration gradient through a partially permeable membrane
- Gasses and small polar molecules can pass through membrane
What is facilitated diffusion?
- The movement of small molecules down a concentration gradient through proteins embedded in the membrane
- Faster than simple diffusion
What is active transport?
- The movement of small molecules across a membrane using energy from ATP, movement is against the concentration gradient
What are the types of simultaneous transport of molecules?
- Symport carrier proteins - Simultaneous transport of molecules in the same direction
- Antiport carrier proteins - Simultaneous transport of molecules in opposite directions
What are the types of proteins used in facilitated diffusion?
- Channel proteins - Water filled pores that allow ion transport
- Carrier proteins - Changes shape when solute binds (much slower than channel)
What is saturation in terms of facilitated diffusion?
- Saturation occurs when all transporters are being used
What are the two types of transport proteins used in active transport and what are their structures? Give an example of each
- P-class transporters: Alpha unit to bind to substrate, unit below accepts phosphate (hydrolysis of ATP). Example, Na+/K+ antiport pump
- ABC transporters: Two binding regions for ATP. Example, eukaryotic MDRs
How does the Na+/K+ pump create and maintain a concentration gradient?
- Active transport to prevent gradient dissipating
- P-class transporters hydrolyses ATP
- Alpha unit of transporter binds to ions, transporter then changes shape allowing Na+ to leave cell/K+ to enter
- 3 Na+ leaves cell but only 2 K+ enters, maintaining electrochemical gradient
How was DNA discovered as the cellular genetic material?
- S-cell solution treated with protease, ribonuclease and deoxyribonuclease
- Transformation of R-cells into S-cells only occurs when DNA is present
- Radioactively labelled viruses used, 35-S in methionine (protein coat) and 32-P in DNA
- Infected E. coli cells only contained 32-P so only DNA is transferred
Describe the structure of nucleotides
- PENTOSE SUGAR - Ribose or 2' deoxyribose (oxygen lost from carbon-2 on main ring)
- NITROGENOUS BASE - Thymine/Cytosine/Uracil (pyrimidine, one ring) or Adenine/Guanine (purine, two rings). Purine pairs with pyrimidine in complementary base pairing
- PHOSPHATE GROUP - Up to three can be added to nucleoside
How are nucleotides joined together?
- Phosphodiester bonds between phosphate group of carbon-5 and hydroxyl group on carbon-3
What are the 10 structural features of B-DNA?
1) Double helix
2) Strands run anti-parallel
3) Complementary base pairing
4) Hydrophobic bases face inwards
5) Hydrophilic sugar-phosphate backbone faces outwards
6) 10 base pairs per turn
7) Length of turn is 3.4nm
8) Width of helix is 2nm
9) Each turn has a major and minor groove
10) The helical structure is right-handed
Which anti-cancer drugs target DNA and how do they work?
- Cisplatin - Covalently binds to guanine to prevent unwinding of DNA, and therefore replication
- Doxorubicin - Becomes intercalated into molecule by sliding in between bases
What is semi-conservative replication and how was it discovered?
- One strand of DNA newly formed and one from parent helix
- Bacteria originally grown on 15-N media (nitrogenous bases have 15-N), then transferred to 14-N media
- DNA separated by density - 1st generation contained 15-N and 14-N
What is the role of a replication fork in DNA replication?
- Replication fork formed when DNA is unwound the origin of replication - start of process
- When two replication forks meet replication is finished
What is the function of topoisomerase enzymes?
- Regulation of underwinding/overwinding of DNA
- Tension from overwinding created after a section is unwound - enzymes releases this tension to prevent it stopping replication
- Type 1: One strand cut then reannealed
- Type 2: Both strands cut, another helix is passed through and then strands are reannealed
What is the function of DNA polymerase III?
- Synthesis of new DNA molecules via replisome
What is the function of DNA helicase?
- H-bonds between base pairs broken using energy
- Allows strand to unwind
What direction can DNA polymerase III work in?
- 5' to 3'
- Leading strand synthesised continuously
- Lagging strand synthesised in Okazaki fragments which are joined by DNA ligase
How does DNA replication begin?
- Primase enzyme makes RNA primer with a free 3' OH group
- Primer attaches to DNA to allow polymerase enzyme to attach and synthesise
- Primer then removed by DNA polymerase I
- Primer replaced by correct nucleotide by DNA polymerase III
Which enzymes to fluoroquinolones affect and what is their method of action?
- DNA gyrase (bacterial topoisomerase enzyme) - relaxes helix after unwinding
- Topoisomerase IV - Cuts strands to unlink replicated circular chromosomes in bacteria
What does Topotecan do?
- Becomes intercalated into DNA and inhibits topoisomerase I
- Used in late stage cervical cancer and relapsed small cell lung cancer
What does Etoposide do?
- Inhibits topoisomerase II
- Used for treatment of testicular cancer/lymphoma
What can DNA polymerase enzymes be used for in a lab setting?
- DNA sequencing
What is meant by the central dogma?
- DNA -> RNA -> Protein, by transcription and translation
What is Rifampicin used for and how does it work?
- Treatment of TB
- Inhibits bacterial RNA polymerase
How are retroviruses treated? Give two examples with the treatments options
- HIV, treated with abacavir
- HSV, treated with acyclovir
- Drugs inhibit action of reverse transcriptase enzyme, preventing RNA being converted to DNA
What are introns and where are they found?
- Non-coding regions of DNA
- Found in pre mRNA
What are exons and what is their function?
- Coding regions of DNA
- Can be combined in various ways to create a protein transcript
How can one gene produce more than one type of protein?
- Introns removed from pre mRNA by spliceosomes
- Exons can be combined in a number of different ways, creating a number of different mature mRNA strands
What are the main features of mRNA?
- At least one transcript per gene
- About 1200 nucleotides in mature mRNA
- Carry message from nucleus to ribosomes
- About 5% of all cells RNA
What are the main features of tRNA?
- About 75 nucleotides in one molecule
- ADAPTOR MOLECULE: transfer amino acids to peptide chain (therefore mRNA to protein)
- Amino acid attached to 3' end of tRNA
- About 15% of cellular RNA
What are the main features of rRNA?
- 1700-3700 nucleotides in one molecule
- "Scaffolding" for ribosomal proteins
- About 80% of cellular RNA
What are the three main phases of transcription?