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Flashcards in Biochemistry Deck (556)
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What is a cell?

Basic structural, functional and biological unit of all living organisms
Smallest unit of life replicate indecently
Require nutrients and produce waste


Describe the cell membrane

Selectively permeable biological membrane separating interior and exterior of cell and protecting from surroundings
Involved in cell adhesion, ion conductivity, cell signalling, attachment surface for cell wall, glycocalyx (glycoprotein-polysaccharide surrounding CM of some bacteria and epithelial) and intracellular cytoskeleton


Describe the phospholipid bilayer

Made of hydrophilic heads and hydrophobic tails
Phospholipids spontaneously form self-sealing bilayers
Due to hydrophobic interior charged ions cannot diffuse
Fluid - components move around easily
Mosaic - variety of lipids and proteins


Describe centrosomes

Associated with nuclear membrane in prophase
In mitosis, NM breaks down and centrosome nucleated microtubules (cytoskeleton) interact with chromosomes to build mitotic spindle
Mother centrosome (oldest) role in making cilia and flagella


Describe lysosomes

Membrane bound organelle that functions as recycling centre by digesting unwanted material in cytoplasm from extracellular and obsolete intracellular components
Contains hydrolytic enzymes capable of digesting almost all biomolecules: proteins, nucleic acids, carbs, lipids, debris
50+ enzymes all active at about pH 5


Describe the cytosol/ICF

Liquid found inside cells separated into compartments by membranes i.e. mitochondrial matrix separates cells into compartments
Eukaryotes - ICF in CM and part of cytoplasm (mitochondria, plastids, organelles minus internal fluids and nucleus


Describe the vacuole

Membrane bound organelle filled with water containing in/organic molecules (enzymes in solution), sometimes engulfed solids
Formed by fusion of multiple vesicles
Shape and function varies depending on needs and type of cell
Role in autophagy, balance between biogenesis and degradation, lysis and recycling of mis-folded proteins


Describe mitochondria

Membrane bound organelles
Main functions are to produce ATP in TCA (respiration) and regulate metabolism
Role in - signalling through mitochondrial reactive O2 specifies
Regulate - MP, apoptosis, Ca signalling (including Ca-apoptosis), cellular metabolism, heme and steroid synthesis
Have oestrogen receptors (mtERs) thus sensitive to hormones
In liver cells, have enzymes that detoxify ammonia (waste product of protein metabolism)


Describe the smooth ER

Site of lipid, phospholipid and steroid synthesis connected to nuclear envelope
Abundant in cells (ovaries, testes, skin oil glands) that secrete these products
Metabolism of carbs and steroids, drug detoxification, attachments of receptors on CMPs
Muscle cell - regulates Ca ion conc.


Describe the cytoskeleton

Dynamic structure made of microfilaments (actin), microtubules (tubulin) and intermediate filaments (only found in animal cells) forming framework for movement of organelles and cell shape


Describe the Golgi body

Modifies, sorts and packages macromolecules for exocytosis or use with in cell primarily those delivered by RER
Transports lipids and involved in creation of lysosomes
N/O-linked goycosylation


Describe the rough ER

Complex responsible for manufacture of lysosomal enzymes (mannose-6-phosphate marker added in cis-Golgi network)
Manufacture of secreted proteins secreted either constitutively (no tag) or regulatory (clathrin and basic AA in signal peptide)
Initial stage of N-linked glycosylation


Describe a vesicle

Variety of functions
Internal environment different from cytosolic as is separate from cytosol thus used for organising cellular substances
Involved in metabolism, transport, buoyancy control, enzyme storage (ready for immediate release), chemical reaction chambers


Describe ribosomes

Site of gene translation
Attaches to mRNA, reads codon. tRNA with complementary anti-codon recruited bringing specific AA building protein.
Continues until reaches stop codon, if none will remain attached forming complex


Describe the nucleus

Cell control centre: maintains integrity of genes and regulates gene expression
Contains DNA and histone proteins to form chromosomes
Has double membrane enclosing entire organelle isolating from cytoplasm, nuclear envelopes and nucleoskeleton (like cytoskeleton)


Describe nucleolus

Organelle found in nucleus that forms around specific chromosomal a previous in nucleus
Made of proteins and RNA
Transcribe and modify rRNA and integrate ribosomal proteins into immature ribosomes
Stress sensor and able to regulate rRNA synthesis based on cell environment


Describe the differences between prokaryotes and eukaryotes

Lack membrane bound nucleus (have nucleoid) and complex organelles
Ribosomal binding site in mRNA is the Shine Delgarno sequence: 8 bases up from AUG
Have mesosomes - folds inwards in PM that increase SA, can be artefact (damage to PM during chemical fixation)
Have cell wall, capsules and flagella (chemotaxis - movement of organism in response to chemical stimuli


Describe gram +ve bacteria (purple)

Thick cell wall of peptidoglycan which is mesh that gives strength
Cell would be spherical and v sensitive to osmotic changes without


Describe gram -ve bacteria (red)

Complex cell wall external to PM with thin peptidoglycan layer
Have outer membrane with lipopolysaccharides conferring
Structural integrity, resistance to chem. attack, toxicity (septic shock, death)


How do many antibiotics work?

Act by inhibiting cell wall synthesis
B-lactam antibiotics (Penicillins) interfere with peptidoglycan synthesis causing cell lysis


What is pH?

Logarithmic measure of conc. of H+ ions (protons) in solution
pH = -log[H+]


What is the physiological pH of the body and why is this important?

pH 7.4
pH affects solubility of substances and the activity of biological systems thus keeping pH constant is important for body
Blood pH<7.3 acidosis
Blood pH>7.5 alkalosis


Define acid, base, conjugated acid and conjugated base

Acid - proton donator, gains -ve charge
Base - proton acceptor, gains +ve charge
Conjugated acid - species formed from addition of H+
Conjugated base - what is left after acid donates proton


What is the major respiratory acid in the body and how is it formed?

Dissolved in water forming carbonic acid which dissociates releasing H+
CO2 + H2O H2CO3 H+ + HCO3-


Name some metabolic acids and how they produced

Organic (lactic, uric) and inorganic (sulphuric) produced by metabolism of AAs containing phosphorus and sulphur
Lactic - product of anaerobic glycolysis
Keto acids - ketoacidosis, lack of insulin
Drugs - aspirin


Define buffer

Solution that resists changes in pH when acid/alkali is added to it
Usually a solution of weak acid and its conjugate base
Biological fluids have ENDOGENOUS buffers


How do buffers work?

Weak acid will partially dissociate and salt will fully dissociate allowing H+/OH- ions to be added and equilibrium will shift to replace the lost molecules
As one fully dissociates more ions will be produced and not removed


What are the main buffers in the body and where are they found?

Haemoglobin (HHb) found in red blood cells
Proteins (HProt) in intracellular fluid
Phosphate (H2PO4-) in intracellular fluid
BICARBONATE (CO2->H2CO3) - blood plasma, interstitial fluid


Define buffer capacity

Extent of resistance to pH change i.e. how much acid/base added before pH changes dramatically


What is the dissociation constant?

Kd - Type of equilibrium constant that measures the dissociation of larger compound to split reversible to smaller components