Proteins + Protein Synthesis Flashcards
What are proteins?
Macromolecule
Peptides made of amino acid molecules and joined by peptide bonds.
Contain C, H, O, N and S
What is the structure of an amino acid?
A carbon attached to a hydrogen, an amine group (NO2), a carboxyl group and an R-group (variable group).
What is meant by primary structure?
The SEQUENCE of amino acids joined together by condensation. Original SEQUENCE of amino acids.
- only has peptide bonds
What is meant by the secondary structure?
Bonds between the molecules depending on the sequence of amino acids.
Alpha helix - hydrogen bonds between the amino acid chain = causes a coil shape
Beta pleated sheet - Peptide chains lie parallel to each other. Hydrogen bonds
What is meant by the tertiary structure?
R-groups interacting to give the final shape of the molecule.
Ionic bonds, disulfide bonds, hydrogen bonds, hydrophobic/hydrophilic interactions.
What is meant by quaternary structure?
Interactions between proteins (called subunits!)
e. g. haemoglobin, insulin
- same interactions as tertiary
Differences between globular and fibrous proteins? (2)
- Globular is soluble while fibrous is insoluble
- Globular is spherical while fibrous is narrow strands
What is an example of a globular protein and what is its function?
Insulin. Regulating blood sugar
What are two examples of conjugated proteins and what are their functions?
Haemoglobin - The red pigment in blood that binds to up to 4 oxygen molecules
Catalase - A catalyst containing 4 haem groups that breaks down hydrogen peroxide
What is the difference between a conjugated and globular protein?
Conjugated a contain non-protein component called a prosthetic group.
What are three fibrous proteins and what are their functions?
Keratin - not 3D, strong and inflexible, found in hair, skin and nails
Collagen - strong and flexible, connective tissue found in skin, tendons, ligaments and nervous system
Elastin - stretchy and flexible, elastic fibres in blood vessels and alveoli
How would you do a chromatography experiment to separate amino acids? (7)
1) Wearing gloves, draw a pencil line at the bottom of the chromatography paper, about 2cm from the edge
2) Mark four equally spaced points along the line
3) Use a capillary tube to spot some amino acid onto the first mark. Let it dry and respot. Label using a pencil
4) Three remaining marks are also spotted
5) Paper is put into the solvent so the paper is only 1cm deep. Cover the jar
6) Paper is left in the solvent until solvent reaches 2cm from the top. Then it is removed and a line is drawn along the solvent front. Let it dry
7) Paper is then sprayed in a fume cupboard with ninhydrin spray. Amino acid reacts with spray and turns purple. The centre of each spot is marked with a pencil.
During a chromatography experiment, why does the student wear gloves?
So that any substances on our fingertips does not interfere with the experiment.
Why is a pencil used instead of a pen for a chromatography experiment?
The ink will bleed out and mix with the substances so pencil is used.
Why was the solvent only 1cm deep?
Chromatography
To ensure it wouldn’t touch the substances and become impure
How do you calculate Rf value?
distance travelled by component/ distance travelled by solvent
What enzyme is used to form polypeptides?
peptidyl transferase
What amino acid has sulphur in its R group
Cysteine
What subunits make up Haemoglobin?
2 alpha
2 beta
- conjugated protein + haem group
What is the function of an R-group?
- Different r-groups
- Causes polarity (or not) or may contain sulfur to change interactions
How are disulfide bonds formed?
- Sulfur - sulfur interaction (two r-groups)
Why is RNA used for protein synthesis? (3)
- DNA is too large to leave pores
- DNA could be damaged in cytoplasm
- RNA is short so it can fit through and the original information won’t be damaged
Method of transcription? (5)
- 5’ to 3’ strand (sense strand) contains needed code
- Antisense strand (complementary) is copied as a template
- So RNA has a copy of the sense strand
- RNA is made from free nucleotides as bases form hydrogen bonds.
- Uracil replaces thymine
Method of translation? (8)
- Ribosomes made of rRNA and protein
- Ribosome attaches to mRNA strand in cytoplasm
- mRNA is read in codons - 3 base triplet code
- tRNA will bind to complementary codon with anticodon to mRNA
- Anticodons join to make peptide bonds (polypeptide chain forms)
- Only 2 can bind at a time so 1st tRNA leaves as 3rd joins
- Bond catalysed by peptidyl translaterase
- Repeats until stop codon reached
How do you form identical polypeptides?
Several ribosomes can pass along mRNA behind the first
