Unit 1 Flashcards
What is a proteome?
Entire set of proteins expressed by a genome
Give two reasons why the proteome is larger than the genome?
- Alternative RNA Splicing
- Post Translation Modification
Describe the structure of an amino acid
- Central Carbon Group
- NH2 Amine Group
- COOH Carboxylic Group
- H
- Variable R group
What are the two main groups present in all amino acids?
Amine Group(NH2) Carboxylic Acid Group(COOH)
What are the four classifications of R groups?
Acidic
Basic
Polar
Hydrophobic
Describe the features of an Acidic R group
Contains a COOH
Negatively charged
What classification of R groups contains an amide group and is positively charged?
Basic
How are amino acids joined together?
Peptide Bonds
What is the primary structure of a protein?
Order of amino acids in a peptide chain
What causes secondary structure?
Hydrogen Bonds
What are the two main folding motifs?
Alpha Helix
Beta Sheet
Describe the Alpha Helix
Helical structure with four residues per turn
Describe the Beta Sheet
Polypeptide chain linked together side by side, can be parallel or antiparallel
Name some of the possible interactions that can cause tertiary structure of the protein
- Hydrophobic
- Ionic
- Hydrogen
- Van der Waals
- Disulphide
Where are hydrophobic interactions typically found?
Towards the inside of the polypeptide
What two molecules do ionic bonds occur between?
COO- and NH3+
What bonds occur between covalent bonds between R groups of Cysteines
Disulphide Bridges
What prosthetic group does Myoglobin contain?
Haeme
Give an example of a protein that contains a carbohydrate prosthetic group?
Glycoprotein
What prosthetic group does Lipoprotein contain?
Lipid
Give an example of a protein that contains a nucleic acid prosthetic group?
Nucleoprotein
What effect does PH have on a protein?
- Affects the concentration of H+ and OH- Ions in solution
- Changes charge of protein
- Places stress on polar interactions such as hydrogen and ionic bonding
- Denature the protein
Give an example of a protein which contains Quaternary structure
Haemoglobin
Describe Quaternary Stucture of a protein
Different subunits of polypeptide chains joined together
What is a Cytoplasmic Protein?
Proteins found in the cytoplasm
Hydrophyllic R groups on the surface
Globular proteins
Example: Enzymes and Hormones
What are the two classifications of proteins at the membrane?
Integral
Peripheral
What is the function of Integral Proteins?
Found within the membrane, act as channels or transporters
How are integral proteins held in the protein?
Strong Hydrophobic Interactions
What is a Ligand?
A substance which can bind to a protein
What charge is the DNA sugar phosphate backbone?
Negatively Charged
What is the name of proteins that can bind to DNA and stimulate or inhibit the transcription of genes
Transcription Factors
What is a Modulator?
Substances which can bind to an enzyme at a site remote from the active site
What type of modulators increase the affinity for the substrate?
Positive Modulators
Describe Polar R groups
Hydrophyllic
Example: C=O, N-H
What causes the increase in kinetic energy of a protein molecule?
Temperature
What effect can increasing the kinetic energy of a protein have?
Places stress on the bonds, breaking them, causing the protein to be denatured
What part of the protein determines the location in a cell?
R groups at the surface of the protein
Where are the hydrophobic R groups found in cytoplasmic proteins?
Clustered towards the middle
How are Peripheral proteins more associated with the heads of the phospholipids?
They contain more hydrophyllic R groups
Where are the R groups not involved in folding found and what is their purpose?
Form areas on the surface
Ligands can bind to them
What is the function of positively charged histomes?
Bind to DNA to form Nucleosomes, allowing the DNA to be packaged in chromosomes
Give an example of how ligand binding can influence the activity of a protein
Induced fit in enzymes
What is Co-operativity?
Co-operativity occurs in proteins with more than one subunit. It is when ligand binding at one subunit alters the conformation of other sub units.
Give an example of a protein where co-operativity occurs
Haemoglobin
Explain the effect of binding of oxygen to one of the sub units in Haemoglobin
- Changes its confirmation
- In turns changes the conformation of the remaining subunits
- -Increasing their affinity for oxygen
- Maximises the O2 uptake in lungs
What is the effect of the release of oxygen from Haemoglobin?
Reduces the affinity of the other subunits
What is a benefit of reducing the affinity of other subunits when oxygen is released from Haemoglobin?
Helps to release oxygen in oxygen depleted environments
Give an example of an oxygen depleted environment
Respiring Tissue
What two conditions can further reduce affinity of haemoglobin subunits for oxygen
Low pH (caused by presence of CO2) High Temperature
What can be added or removed from particular R groups to cause reversible conformational change in proteins?
Phosphate
What type of modification is Phosphorylation an example of?
Covalent modification and post translation modification
What can Phosphorylation help to regulate?
The activity of many cellular proteins
What is the function of a Kinase?
Catalyse Phosphorylation, by transferring phosphate from ATP to the protein
What is the name for the enzymes that catalyse de-phosphorylation?
Phosphatase
Where are ATPases found?
Membrane, as are membrane bound
What and how do ATPases use phosphate for?
ATPases use phosphate to phosphorylate themselves, and they use it to change their confirmation and alter their activity
What is a use of transmembrane ATPases?
Active transport of ions and the sodium potassium pump
What triggers the movement of Myosin?
Conformational changes due to ligand binding
What does movement of Myosin cause?
The movement of finer actin filaments
Describe the process of Muscle Contraction
- Myosin heads are bound to the actin, forming cross bridges
- Binding of ATP occurs, causes a conformational change, myosin heads detach from the actin and swing forward
- ATP is broken into ADP + Pi. They remain bound to the myosin and cause a second conformational change. The myosin acts as an ATPase
- Myosin rebinds to the actin but at a further position along the filament. A third conformational change occurs.
- ADP + Pi are released. Myosin head returns to original confirmation, dragging the actin filament along
What type of substances are able to diffuse directly through the bilayer in a membrane?
Hydrophobic
Give an example of a molecule that can diffuse directly through the membrane bilayer
Oxygen, Carbon Dioxide, Water, Steroid Hormones
Give an example of a molecule that requires a membrane protein to move it across the membrane
Glucose, Charged Molecules such as Na+, K+ and Ca2+
Can membrane proteins create/maintain concentration gradients?
Yes
What are the two types of membrane proteins?
Channels, Transporters
Describe Channel Proteins
Transmembrane proteins, passage is always passive through them
They can be gated or ungated
Give an example of an ungated protein
Aquaporin
What are the two ways gated channels can be controlled?
Ligand Gated
Voltage Gated
Describe Ligand Gated Channel Proteins
Binding of a ligand triggers conformational change
Example: Neurotransmitters act as ligands when binding to receptors in post synaptic neurons, which open to allow sodium ions in
How are voltage gated channels opened and closed?
Changes in Ion Concentration across the membrane
Explain the difference between transporters and channels
Channels - molecule binds to channel to allow other molecules to move through
Transporters - molecule binds to transporter so it can move through
Are transporters specific?
Yes, very
If a transporter moves molecules passively what is this known as?
Facilitated Diffusion
Give an example of a transporter and where it can be found
GLUT 4 transporter
Found in Fat and Muscle Cells
Define ‘Coupled Transport’
The movement of two molecules together across a membrane
What is the difference between a symport and an antiport?
A symport moves both molecules in the same direction, and antiport moves them in opposite directions
Give an example of coupled transport and state the two molecules, the name of the transporter and whether the transporter is an antiport or a symport
Glucose Symport
- Transfers Na+ and Glucose
- Symport
- Found in cells lining small intestine
In the glucose symport, does sodium move up or down its concentration gradient?
Down
What happens when Na+ binds to the Glucose Symport?
causes a conformational change which pushes both sodium and glucose across the membrane
How do cells maintain the gradient of sodium required for the glucose symport?
Using an active transport protein, known as the sodium potassium pump(Na+/K+ ATPase)
Where does the Sodium Potassium ATPase get its energy from?
The hydrolysis of ATP
Describe the direction of the Sodium Potassium Pump
Sodium out, Potassium In
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