2.4 Proteins Flashcards
What is the monomer that forms proteins?
Amino Acids
What is the structure of an amino acid?
Central carbon bound to:
- An amine group (NH2)
- A carboxyl group (COOH)
- A hydrogen atom
- A variable side chain (R)
How many amino acids exist universally?
20
What do we call a chain of amino acids?
Polypeptide
Are polypeptides polar?
They differ in structure, some are some are not
What type of bond holds amino acids together?
(Covalent bonds) called peptide bonds
How are polypeptides broken down?
Hydrolysis
Between which groups do peptide bonds form?
Carboxyl and Amine group
What is the primary structure of amino acid sequences?
The order
What is the secondary structure of amino acid sequences?
How the amino acids are folded
What is the tertiary structure of amino acid sequences?
The overall 3D configuration
What is the quaternary structure of amino acid sequences?
The structure including any other polypeptide strands which may or not be present
What are the two stable configurations of amino acid secondary structures?
Alpha helices
Beta-pleated sheets
Describe alpha helix structure
Amino acids fold in a coil/ spiral arrangement
Describe beta-pleated sheets
Directionally-oriented staggered strand conformation
How do alpha helices and beta pleated sheets form?
Hydrogen bonds form between non-adjacent amine and carboxyl groups
What determines the tertiary strucutre?
Interactions between the variable chains
Give an example of a protein with a quaternary structure
Haemoglobin
4 polypeptide chains and an iron-containing haeme group
What is a prosthetic group?
A non amino-acid component that is part of a protein
Define denaturation
Is a structural change in a protein that results in the loss (usually permanently) of its biological properties
Which two factors can cause denaturation?
pH
temperature
How does temperature cause denaturation?
High levels of thermal energy can break the hydrogen bonds
How does pH cause denaturation?
The pH can alter the charge of the protein, altering it’s solubility and shape
What is the process of converting a gene sequence into a polypeptide?
Transcription
Translation
How many polypeptides do genes typically code for?
Usually 1 but there are exceptions
When do genes code for more than one polypeptide?
- Genes may be alternatively spliced to generate multiple polypeptide variants
- Genes encoding tRNA sequences are transcribed but never translated
- Genes may be mutated and consequently produce an alternative polypeptide sequence
What is the proteome?
The totality of proteins expressed within a cell, tissue or organism at a certain time
Why may a proteome be significantly larger than the number of genes?
- Alternative splicing (creating more than one protein from a single gene)
- Modification after translation to promote further variants
What purposes may a protein serve?
Structure Hormones Immunity Transport Sensation Movement Enzymes
