MGD S1 - Cell structure, Amino acids and Proteins Flashcards
Ribosome function?
Ribosomes interpret cellular information from the nucleus and synthesise proteins. There are different types of ribosomes (80s eukaryotic, 70s prokaryotic)
Microfilament function?
- Made up of actin
- In non-muscle cells the actin makes up a web-like layer, the cell cortex, located immediately below the cell’s plasma membrane
- The structure helps define the shape of the cell
- They also facilitate the movement of certain particles and structures i.e macrophages, fibroblasts and nerve growth cones
Microtubules function?
- Made ups of α-tubulin and β-tubulin dimers
- dynamic structure
- The main ‘building blocks’ forming the cytoskeleton
- The cells framework within which all components of the cell are held in position or allowed restricted movement
- Movement of materials and structures within cells Eg help form the mitotic spindle during prophase
Intermediate filament function?
- Important for maintaining the mechanical structure of cells
- There are different types occurring in different cells and therefore provide structural support in slightly different ways
Centrosome function?
Contain the centrioles, which are involved in the process of mitosis
Nucleus function?
- Control centre of the cell
- Contains cell’s DNA in the form of genes
- Sequestration of DNA and replication of DNA
- Transcription and modification of RNA
Rough endoplasmic reticulum function?
- Consists of many interconnected membranous sacs called cisternae, onto which ribosomes are attached In the lumen of the cisternae.
Produce proteins that are either:
1) Retained within vesicles
2) Secreted from the cell
Smooth endoplasmic reticulum function?
- Many enzymes attached to the surface of the the cisternae or located within Chemical reactions within the SER vary with the type and location of cells
- Helps with protein folding
- Glycosylation - involves the addition of oligosaccharides
- Disulphide bond formation and rearrangement - to stabilise the tertiary and quaternary structure of many proteins
- Modification of some drugs EG by the cytochrome P450 enzyme in liver cells
Lysosome function?
1) Autophagy - Digestion of materials within the cells
2) Heterophagy - Digestion of materials originating from outside the cell
3) Biosynthesis - recycling unwanted products of chemical reactions to process materials received from outside the cell Lysosomes also destroy the cell - usually after it has dies
Peroxisome function?
Similar to lysosome but also include:
- β-oxidation of fatty acids
- Breakdown excess purines to urea
- Breakdown of toxic compounds Eg in the cells of the liver and kidney
- Plays a role in the biosynthesis of cholesterol and bile acids derived from cholesterol
Vesicle function?
Transport and deliver contents (hormones and neurotransmitters etc) either into or out of the cell, via the cell membrane
What are the 4 types of non-covalent interactions that help bring molecules in a cell together?
1) Electrostatic interaction - attractive forces between oppositely charged atoms
2) Hydrogen bonds - special form of polar interaction where an electropositive hydrogen atom is partially shared by two electronegative atoms. It hydrogen can be seen as a proton that has partially disassociated from a donor atom, allowing it to be shared by a second acceptor atom
3) van der Waals attractions - Spontaneous polar interactions
4) Hydrophobic interaction - caused by pushing of non-polar surfaces out of the hydrogen-bonded water network, where they would interfere with the highly favourable interactions between water molecules
How many amino acids are there?
20
How are amino acids linked?
Covalent peptide bonds
Define aliphatic
Hydrocarbons arranged in a linear chain
Define aromatic
Closed hydrocarbon chain
What is an amphipathic molecule?
Molecule containing both hydrophilic and hydrophobic regions
Define pH
Concentration of H+ ions in solution pH= -log(H+)
What is the purpose of a buffer?
Solution made of weak acid and its conjugate base that resists changes in pH upon the addition of small amounts of acid or alkali
What is the isoelectric point of a protein?
pH at which the protein has no net charge Acidic proteins have a low Pi and basic protein have a high Pi
Describe the structure of an amino acid
- Central alpha carbon atom
- Amino group
- Carboxyl group
- R group
What happens to an amino acid with a Pi lower than the pH of solution?
Amino acid is deprotonated
How are amino acids classified?
Polar, non-polar, aliphatic, aromatic, charged, uncharged
Name two non-polar amino acids?
Phenylalanine and Tryptophan
Name two negatively charged amino acids
Glutamate and aspartate
Name two positively charged amino acids
Lysine and arginine
What is a peptide bond? List the features of a peptide bond
- Covalent linking of two amino acids between the carboxyl group of one and the amino group of the other with the subsequent removal of a water molecule
- Peptide bonds are planar, in trans arrangement and have double bond properties due to delocalisation of electrons
What is the consequence of a change in the primary structure of a protein?
Altering the sequence of amino acids can impact the secondary and tertiary structure leading to a non-functional polypeptide
List the key features of an alpha helix
1) Right handed
2) R groups on the outside of the helix
3) 3.6 amino acids per turn
4) 0.54 nm pitch
5) Stabilised by hydrogen bonds
List the key features of a beta pleated sheet
1) Extended conformation
2) Parallel or antiparallel
3) Interconnecting hydrogen bonds between each
4) R groups alternate between opposite sides of the chain
5) 0.35nm pitch
Name two helix forming amino acids
Alanine and leucine - small hydrophobic residues
Name two helix breaking amino acids
Glycine - Small R groups support other conformation
Proline - non-rotation around C-N bond
List the essential amino acids
If Learnt, This Huge List May Prove Truly Valuable
Isoleucine Leucine Tryptophan Histidine Lysine Methionine Phenylalanine Threonine Valine
Describe the differences between globular and fibrous proteins and give examples of each
Globular - different secondary structures, compact, for catalysis and regulation Eg enzymes
Fibrous - One type of secondary structure, long strands or sheets, for shape and support Eg collagen
What are amyloidosis?
Accumulation of mis-folded or altered dysfunctional proteins which cause disease
