Studied by 4 peopleWhat are the monomers of proteins?
Amino acids
Dipeptide
Two amino acids bonded together
Polypeptide
A polymer (chain) of more than two amino acids bonded together
What are proteins made of?
One or more polypeptides
What is the general structure of amino acids?
A carboxyl group, an amine/amino group, a carbon-containing R group
How many amino acids are there?
20
What is the difference between amino acids?
Their R group
How are amino acids linked?
Condensation reaction
What is released in a condensation reaction?
Water molecule
What type of bond is formed between amino acids?
Peptide bond
What are the 4 structural levels of proteins?
Primary, Secondary, Tertiary, Quaternary
What is the primary structure of a protein?
The sequence of amino acids in the polypeptide chain
What is the secondary structure of a protein?
The 2D arrangement of the chain of amino acids. Alpha helix or Beta pleated sheet
What determines the secondary structure of a protein?
Hydrogen bonds between amino acids
What is the tertiary structure of a protein?
The 3D structure of a protein
What determines the tertiary structure of a protein?
Hydrogen bonds, ionic bonds, disulphide bridges, hydrophobic and hydrophilic interactions
What is the quaternary structure of a protein?
Some proteins are made of more than one polypeptide chains linked together. The quaternary structure is the way these polypeptide chains are assembled together
What is the primary structure of proteins held together by?
Peptide bonds between amino acids
Ionic bonds in proteins
Attractions between negative and positive charges on different parts of the molecule
Disulphide bridge/bond in proteins
Covalent bond between sulphur atoms of two cysteine amino acids
Hydrophobic interactions in proteins
When hydrophobic groups are close together, they tend to clump together
Hydrophilic interactions in proteins
Hydrophilic groups get pushed to the outside
What do hydrophilic/phobic interactions affect tertiary structure?
They affect how the protein folds up
How does a proteins primary structure determine its 3D structure and properties
The amino acid sequence of a protein determines what bonds will form and how the protein folds into its 3D structure. The 3D structure determines its properties and function in the body
Globular proteins
Round, compact proteins made up of multiple polypeptide chains.
Complex tertiary/quaternary structures.
Form colloids in water
How are the chains structured in globular proteins?
Coiled up so that hydrophilic parts are on the outside and hydrophobic parts face inwards
What are the two types of protein 3D structure?
Globular Fibrous
How does the structure of globular proteins make it good for their function?
Makes them soluble, so they're easily transported in fluids
Hydrogen bonds
Weak bonds between a slightly positively charged hydrogen atom in one molecule and a slightly negatively charged atom in another molecule
Example of globular protein
Haemoglobin
Haemoglobin strucutre
Globular protein made of 4 polypeptide chains. It has iron-contains haem groups that bind to oxygen
What is the function of haemoglobin?
Carries oxygen around the body
How is haemoglobin suited for its function?
Its soluble so can easily be transported in the blood
Collagen structure
Fibrous protein made up of 3 polypeptides
Fibrous proteins
Long, insoluble polypeptide chains, tightly coiled round each other to form a rope shape
Chains are held together by lots of bonds, making the proteins strong
Little tertiary/quaternary structure
Occasional cross linkages which forms microfibres for tensile strength
Insoluble
How are fibrous proteins suited for their function?
They are strong so are often found in supportive tissue
How is collagen suited for its function?
High tensile strength due to hydrogen and covalent bonds and forms the structure of bones, cartilage and connective tissue in animals
What do enzymes do?
Catalyse metabolic reactions
Intracellular enzymes
Catalyse reactions inside the cell
Extracellular enzymes
Secreted by cells to catalyse reactions outside of cells
Are enzymes proteins?
Yes
Activate site of enzymes
Has a specific shape where the substrate molecules bind to
What makes enzymes specific?
Their tertiary structure
How do enzymes catalyse reactions?
They lower the activation energy needed for a reaction
Enzyme-substrate complex
A complex formed when an enzyme binds to its substrate molecule(s).
Activation energy
Energy needed to get a reaction started
How does an enzyme substrate complex lower activation energy?
If 2 substrate molecules need to be joined, being attached to the enzyme holds them close together, reducing and repulsion between the molecules so they can bond more easily
In a breakdown reaction, fitting into the active site puts a strain on the bonds in the substrate so the molecule breaks up more easily
Induced fit model
Change in the shape of an enzyme's active site that enhances the fit between the active site and its substrate(s)
How do enzyme properties relate to their tertiary structure?
Enzymes are very specific and usually only catalyse one reaction because only one complementary substrate will fit into the active site
The enzyme's active site is determined by it's tertiary structure
Each enzyme has a different tertiary structure and so a different shaped active site
If the substrate doesn't match the active sit, the enzyme-substrate complex won't be formed and the reaction won't be catalysed
What can the tertiary structure of an enzyme be altered by?
Changes in pH or temperature
What is the primary structure of a protein determined by?
The sequence of nucleotides in the gene encoding for amino acids
How does enzyme concentration affect enzyme activity?
The more enzyme molecules there are in a solution, the more active sites present and the more likely a substrate molecule is to collide with an active site and form an enzyme-substrate complex
What is the limiting factor in enzyme catalysed reactions?
Substrate concentration
What does DNA stand for?
Deoxyribosenucleic Acid
What does RNA stand for?
Ribonucleic acid
What are mono nucleotides made from?
Pentose sugar
Nitrogen-containing organic base
Phosphate group
Pentose sugar
Sugar with 5 carbon atoms
DNA and RNA are polymers of what?
Mononucleotides
What is the pentose sugar in a DNA mononucleotide called?
Deoxyribose
Each DNA mononucleotide has the same _____ and a ____/
Sugar
Phosphate group
What varies between DNA/RNA mononucleotides?
Their base
4 bases (DNA)
Adenine (A)
Thymine (T)
Cytosine (C)
Guanine (G)
What is the pentose sugar in a RNA mononucleotide called?
Ribose
Each RNA mononucleotide has the same _____ and a ____/
Sugar
Phosphate group
4 bases (RNA)
Adenine (A)
Uracial (U)
Cytosine (C)
Guanine (G)
Polynucleotide
A polymer consisting of many mononucleotide monomers in a chain
What are polynucleotides joined by?
Condensation reaction between the phosphate of one mononucleotide and the sugar group of another
How many polynucleotide strands is DNA made up of?
Two
How many polynucleotide strands is RNA made up of?
One
How do two DNA polynucleotide strands join together?
Hydrogen bonding between bases
What are the DNA base pairs?
Adenine - Thymine (A-T)
Cytosine - Guanine (C-G)
Complementary base pairing
Hydrogen bonding between particular pyrimidines and purines
Pyrimidines
Cytosine
Thymine
Uracil
Purines
Adenine
Guanine
How many hydrogen bonds form between A and T?
Two
How many hydrogen bonds form between C and G
Three
DNA double helix
Two antiparallel polynucleotide strands twist to form the DNA double-helix
Who and when determined the double-helix structure of DNA
Watson and Crick - 1953
Gene
Sequence of mononucleotide bases on a DNA molecule that codes for the sequence of amino acids in a polypeptide
Different proteins have a different ______ and _____ or amino acids
Number
Order
How many bases code for one amino acid?
Three
Does DNA move out of the nucleus?
No, It is too large so is copied into mRNA (transcription). The mRNA leaves the nucleus and joins with a ribosome in the cytoplasm, where it can be used to synthesise a protein (translation)
Two types of RNA
Messenger RNA (mRNA)
Transfer RNA (tRNA)
When and where is mRNA made?
In the nucleus during transcription
What does mRNA do?
Carries the genetic code from the DNA to a ribosome in the cytoplasm, where it's used to make a protein during translation
Codon
A specific sequence of three adjacent bases on a strand of DNA or RNA that provides genetic code information for a particular amino acid
Where is tRNA found?
The cytoplasm
What does tRNA have at each end?
Amino acid binding site at one end and an anticodon at the other end
Anticodon
A sequence of three bases of a tRNA molecule that pairs with the complementary three-nucleotide codon of an mRNA molecule during protein synthesis.
What does tRNA do?
Carries the amino acids that are used to make proteins, to the ribosomes during translation
What are codons and anticodons sometimes referred to as?
Triplets
Genetic code
The sequence of base triplets (codons) in DNA or mRNA which codes for specific amino acids
Features of genetic codes
Degenerate (more than one genetic code corresponds to one amino acid)
Non-overlapping (base triplets don't share their bases, each is separate from the triplet before)
How many possible triplets are there?
64
Start and Stop codons
Triplets used to tell the cell when to start and stop the production of the protein. Found at the beginning and end of the gene
What is the first stage of protein synthesis called?
Transcription
Stage 1 of transcription:
Transcription starts when RNA polymerase attaches to the DNA double-helix at the beginning of a gene (start codon)
Transcription starts when RNA polymerase attaches to the DNA double-helix at the beginning of a gene (start codon)...
Stage 2 of transcription:
The hydrogen bonds between the two DNA strands in the gene break, separating the stands and causing the DNA molecule to unwind.
The hydrogen bonds between the two DNA strands in the gene break, separating the stands and causing the DNA molecule to unwind...
Stage 3 of transcription:
One of the strands is used as a template to make an mRNA copy
One of the strands is used as a template to make an mRNA copy...
Stage 4 of transcription:
RNA polymerase lines up free RNA mononucleotides alongside the template strand. Complementary base pairing means the mRNA ends up being a complementary copy of the DNA strand (with T being replaced with U)
Note
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