Proteins Flashcards
what are proteins made of
Long chains of amino acids
what are amino acids
monomers from which proteins are made.
what is a dipeptide
who two amino acids join together
what is a polypeptide
when two or more amino acids join together.
What is the general structure for amino acids
NH2- amine group, COOH- carboxyl group and R- variable side chain
how do the 20 amino acids differ
differ only in their side group
how are amino acids linked together
by condensation reaction to form polypeptides. A molecule of water is released during the reaction .
What are
the bonds that are formed between the amino acids called
peptide bonds
what kind of reaction is it when the peptide bond is broken in a dipeptide.
hydrolysis
what are the four structural levels of proteins
Primary, secondary, tertiary, quaternary.
what is the primary structure of proteins
sequence of amino acids in the polypeptide chain
what is the secondary structure of proteins
the polypeptide chain doesn’t remain flat and straight.
-Hrogen bonds form between the amino acids in the chain.- making it automatically coil into an alpha helix or fold into a beta pleated sheet- this is the secondary structure.
what is the tertiary structure of proteins
coiled and folded further. more bonds form, including hydrogen bonds and ionic bonds(attractions between negative and positive charges on different parts of the molecule)
what is the quaternary structure of proteins
made of several different polypeptide chains held together by bonds. examples include haemoglobin, insulin and collagen, 3D shape
what is the structure and function of enzymes
usually roughly spherical in shape due to the tight folding of the polypeptide chains. They are soluble and often have roles in metabolism.g breaking down large food molecules- digestive enzymes. or help to synthesise large molecules
examples of proteins
Enzymes
Antibodies
Transport proteins
structural proteins
what is the structure and function of antibodies
ivolved in immune response, made up of two light(short) polypeptide chains and two heavy(long) polypeptide chains bonded together. Antibodies are variable regions- the amino acid sequences in these regions vary greatly
what is the structure and function of transport proteins
e.g channel proteins in cell membranes- contain hydrophobic and hydophilic amino acids which cause the protein to fold up and form a channel. These proteins transport molecules and ions accross a membrane
what is the structure and function of structural proteins
physically strong. Consist of long polypeptide chains lying parallel to each other with cross-links between them. Examples include keratin (hair and nails) and collagen( found in connective tissue)
what is the test for proteins
add sodium hydroxide solution because the test must be alkaline
then add copper sulphate solution, if present turns purple if not stays blue
what are enzymes
biological catalysts, they catalyse metabolic reactions at both cellular level and for an organisms as a whole
what is formed when a substate fits into an enzymes active site
an enzyme-substate complex
how does an enzyme reduce the activation energy needed
if the two substrate molecules need to be joined, being attached to an enzyme holds them closer together, reducing any repulsion between the molecules so they can bond more easily.
If the enzyme is catalysing breakdown reaction, fitting into the active site puts a strain on bonds in the substate, so the substate molecule breaks up more easily.
how is the induced fit model different to the lock and key
enzymes are specific and only bond to one particular substate. The substate has to make the active site change shape in the right way.
what are the properties of enzymes
very specific- only catalyse one reaction.g maltase only breaks down maltose.- this is because only one complementary substrate will fit into the active site.
The active sites shape is determined by the tertiary structure.
If the tertiary stricture is altered in any way, the shape of the active site will change. If a mutatuion occurs in a gene the primary structure could be affected therefore effecting the tertiary structure.
how is the primary structure of a enzyme determined
a gene
how does temperature influence enzyme activity
more heat means more kinetic energy, so the molecules move faster. The enzyme is more likely to collide with the substrate molecules. energy of these collisions also increases, each collision is more likely to result in a reaction.
how would too much temperature effect enzyme activity
rise in temp- enzyme molecules vibrate more.
if the temperature goes above a certain level, this vibration breaks some of the bonds that hold the enzyme shape. active site changes shape. enzyme and substrate no longer fit together.- enemy is denatured.
how does Ph effect enzyme activity
All enzymes have an optimum pH value. Most work best at pH7(neutral). Exceptions include pepsin- acidic 2- found in stomach.
above and below optimum pH the H+ and OH- ions found in acidic ad alkalis can mess up the ionic bonds and hydrogen bonds that hold the enzymes tertiary structure in place. Making the active site change shape- denature.
How does Enzyme concentration affect the Rate of reaction
The more enzyme molecules tare are in a solution, the more likely the substrate molecule is to collide with one and form n enzyme-substrate complex. increasing the concentratetion of the enzyme increases the rate of reaction.
If the amount of substrate is limited . comes to a point where there’s more than enough enzyme molecules to deal with all available substrate, so adding more enzyme has no effect
why does the substrate concentration effect the rate of reaction up to a point
higher substrate conc- faster reaction; collisions between the substrate and enzyme more likely. only true up to a ‘saturation’ point. Active sites are full, adding makes no difference.
Substrate conc decreases with time, if no other variables trade of reaction will decrease over time. makes initial rate of reaction the highest.
what are enzyme inhibitors
molecules that bind to the enzyme that they inhibit. can be competitive or non competitive.
how do competitive inhibitors affect enzyme activity
have a similar shape to the substrate, compete with the substrate molecules to bind to the active site, but no reaction takes place, instead blocking the active site , so no substate molecule can fit in.
How much the enzyme is inhibited depends on the relative concentrations of the inhibitor and the substrate
how do non-competitive inhibitors effect the rate of reaction
bind to the enzyme away from its active site, causes active site to change shape so the substrate molecules can no longer bind to it.
increasing conc of substarate won’t make any difference to the reaction rate.
What is DNA
deoxyribonucleic acid is used to store genetic genetic info- all the instructions an organisms needs to grow and develop
what is RNA
ribonucleic acid- similar to the structure of DNA , main function is to transfer genetic information from the DSNA to the ribosomes. Ribosomes read the RNA to make polypeptides (proteins) in a process called translation.
what is a nucleotide made from
A pentose sugar (sugar containing 5 carbon atoms)
a nitrogen- containing organic base
a phosphate group
what is the pentose sugar in a DNA nucleotide called
deoxyribose
each nucleotide has the same sugar and a phosphate group. the base on each nucleotide varies
what are the four possible bases for a DNA nucleotide
Adenine, Thymine, cytosine and guanine
what is the name of the sugar in a RNA
ribose sugar
what are the four different bases n RNA
Adenine, Uracil ,cytosine and guanine
what is the name of a polymer of nucleotides
polynucleotide
what reaction forms polynucleotides
condensation between the phosphate group of one nucleotide and the sugar of another forming an ester bond
what is the chain of sugar and phosphates known as
sugar-phosphate backbone
what is it called when each base can only join with one particular partner
complementary base pairing
what are the different complementary base pairings
adenine and thymine (A-T) and Cytosine and Guanine (C-G). Meaning there is always equal amounts of Adenine and thymine and Cytosine and Guanine
what bonds form between A and T
two hydrogen bonds
what bonds form between C and G
three hydrogen bonds.
what word desbrides the way the two strands on polynucleotide strands twist to. form a double Helix
Antiparallel
who discovered the double helix structure
Waste and Crick
what enzyme splits the two strands in a semi conservative replication
DNA helicase- breaks the hydrogen bonds making the helix unwind
what happens in stage 2 of DNA replication
original strand acts as a template, in leading strand enzyme primer produces a primer- short piece of DNA- this acts as the start point for dNA synthesis. Then DNA polymerase binds to the leading strand and walks along it adding complementary base pairings in 5’ to 3’ direction
what are the two strands called
leading is top lagging is bottom
what happens in stage 3 of DNA replication Numerous primers are made on lagging strand due to the direction being 3’ to 5’
DNA polymerase then adds a series of complementary bases in 5’ to 3’ direction using the different primers as a starting point, then the enzyme exonuclease removes all the primers, then another DNA polymerase fills in all the gaps left behind with DNA. Enzyme ligase then seals up the DNA in both strands.
who validated semi conservative replication
Meselson and Stahl
DNA contains heavy nitrogen and light nitrogen
how did meselson and Stahls experiment work
two samples of bacteria- one in a nutrient broth containing light nitrogen and one in a broth containing heavy nitrogen
