LGS A-Level OCR Biology - Unit 2 - Proteins
The secondary structure of a protein is formed by the folding or coiling of the primary amino acid chain, held together by hydrogen bonds. This creates structures such as α-helices and β-pleated sheets.
What are the monomeric units of proteins?
Amino acids
Key Terms
What are the monomeric units of proteins?
Amino acids
Where do we get amino acids from?
Our diet
Outline the journey an amino acid takes from food to protein in a cell
food is ingested
enzymes in the stomach/small intestine hydrolyse protein into amino acids
the amino acids are absorbed by the gut wall...
How many common amino acids are there?
20
Give 4 functions of proteins
enzymes
hormones
antibodies
structural proteins
What do the interactions of differing R-groups determine?
The folding of the protein
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| Term | Definition |
|---|---|
What are the monomeric units of proteins? | Amino acids |
Where do we get amino acids from? | Our diet |
Outline the journey an amino acid takes from food to protein in a cell | food is ingested enzymes in the stomach/small intestine hydrolyse protein into amino acids the amino acids are absorbed by the gut wall into the blood the amino acids leave the blood in the tissue fluid and enter cells proteins are synthesised on the ribosomes |
How many common amino acids are there? | 20 |
Give 4 functions of proteins | enzymes hormones antibodies structural proteins |
What do the interactions of differing R-groups determine? | The folding of the protein |
What type of reaction occurs to form a protein from 2 amino acids? | Condensation |
What type of bond is formed from the synthesis of a protein? | Peptide |
What is produced in the condensation reaction between two amino acids? | Water and dipeptide |
What is the general formula of an amino acid? | |
Between which parts of the amino acid molecules does the condensation reaction between two amino acids occur? | The carboxyl group of one amino acid and the amine group of another amino acid |
What is a chain of amino acids called? | A polypeptide |
What is the end of a polypeptide with an amino group called? | The N-terminus |
What is the end of the polypeptide with a carboxyl group called? | The C-terminus |
What is the definition of primary structure of a protein? | The SEQUENCE of amino acids |
What type of bonding holds the primary structure of a protein together? | Peptide |
What shape is the primary structure of a protein? | Linear |
What forms the secondary structure of a protein? | The folding of the primary structure |
What type of bonds hold together the secondary structure of a protein? | Hydrogen bonds |
In the secondary structure, what do hydrogen bonds form between? | Partially positive H and partially negative O |
What are the two possible shapes of the secondary structure? | alpha helix beta pleated sheet |
What is the tertiary structure formed by? | The folding of the secondary structure |
Why do proteins fold at the tertiary level of structure? | Due to the interactions between the R-groups |
What are the 4 types of bond formed at the tertiary level of structure? | ionic bonds hydrogen bonds disulfide bonds hydrophobic and hydrophilic interactions |
What do ionic bonds form between? | Positively and negatively charged ions |
What do hydrogen bonds form between? | Partially positive H and partially negative O |
What do disulfide bridges form between? | Sulfur atoms contained within R-groups |
Which amino acid contains sulfur? | Cysteine |
What do hydrophobic and hydrophilic interactions form between? | Polar and non-polar R-groups |
What kind of shape does the tertiary structure have? | 3D |
What forms the quaternary structure? | Formed by the interaction of more than one tertiary protein and/or with prosthetic groups |
What type of bonds holds together the quaternary structure? | -ionic -hydrogen -disulfide -hydrophobic and hydrophilic interactions |
What is a prosthetic group? | a non-protein component of a conjugated protein |
Define simple proteins | Proteins without a prosthetic group |
Give 3 characteristics of globular proteins | -compact -water soluble -roughly spherical |
Why are globular proteins water soluble? | -TERTIARY structures are folded so that the hydrophobic R-groups are kept away from the aqueous environment -hydrophilic R-groups are on the outside |
What are globular proteins used for? | -regulating many processes |
Give examples of the processes globular proteins regulate | -muscle contraction -immunity -chemical processes |
Give an example of a globular protein | Insulin |
Why is it beneficial for insulin to be water-soluble? | -insulin is a hormone -hormones are transported in the blood so must be water soluble |
What is the function of insulin? | Regulates blood glucose |
Are conjugated proteins a type of globular protein? | Yes |
What do conjugated proteins contain? | A non-protein prosthetic group |
Give an example of 2 conjugated proteins | Haemoglobin Catalase |
What is the function of haemoglobin? | Carries oxygen in the blood in erythrocytes |
What is haemoglobin made up of? | 2 alpha-helices 2 beta-pleated sheets |
How many subunits make up haemoglobin? | 4 |
What does each haem group contain? | Iron 2+ ion |
What does each subunit of haemoglobin contain? | A haem group |
How do haem groups allow erythrocytes to carry out their function? | Iron ions in haem groups can reversibly combine with an oxygen molecule |
How many oxygen atoms can one haemoglobin molecule carry? | 8- remember ATOMS not MOLECULES |
Define globular protein | spherical, water-soluble proteins |
Define fibrous protein | long, insoluble, structural proteins |
What is the function of catalase? | Break down of hydrogen peroxide which otherwise is harmful to cells |
What type of protein is catalase? | Conjugated |
What type of prosthetic group does catalase contain? | Haem |
How many haem groups does catalase contain? | 4 |
Give 3 examples of fibrous proteins | Collagen Elastin Keratin |
Where is Keratin found? | In hair, skin, and nails |
How does the primary structure of repetitive amino acid sequences affect the properties of fibrous proteins? | -gives them organised structures -makes strong molecules that do not fold into complex 3D shapes |
Which amino acid does keratin contain in a high proportion? | Cysteine |
What does Cysteine contain in its R-group? | Sulfur |
What type of bonding occurs a lot in keratin? | Disulfide bonds |
How does a high proportion of disulfide affect the properties of keratin? | It makes it inflexible and strong |
Where is elastin found? | In the walls of blood vessels and alveoli of lungs |
What does elastin allow tissues to do? | Expand and return to size |
Why is it beneficial for tissues to contain elastin? | It confers strength and elasticity |
What makes up elastin? | Aggregates of tropoelastin |
Where is collagen found? | In the skin, tendons, ligaments, and nervous system |
Why does collagen contain glycine for every 3rd amino acid? | Glycine is the smallest amino acid and so they can pack together more tightly |
What property does collagen have? | Flexibility |
Define polypeptide | Chains of 3 or more amino acids |
Define protein | one or more polypeptides arranged as a complex macromolecule |