Levels of Protein Structure Primary 1º Structure The primary structure is simply the sequence of amino acids in a protein Chains of amino acids are written from the amino terminus Nterminus to the carboxyl terminus Cterminus ID: 536915
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Slide1
Lesson 5 – ProteinsLevels of Protein StructureSlide2
Primary 1º Structure
The primary structure is simply the sequence of amino acids in a protein.
Chains of amino acids are written from the amino terminus (N-terminus) to the carboxyl terminus (C-terminus).Slide3
Usually the amino acids are represented by their 3 letter abbreviations. Less commonly you will see the full name of each amino acid or even the single letter designations.Slide4
Secondary 2º Structure
There are 2 types of secondary structure
α
-helix and
β
–sheet.Slide5
α-helix
The helix is right handed with 4 residues (amino acids) per turn.
Hydrogen bonds between oxygen (the C=O group) and hydrogen (N-H group) stabilise the helix.Slide6
β-Sheet
Polypeptide chains are linked together in a side by side formation with hydrogen bonds.
Hydrogen bondsSlide7
β-Sheet
β
-sheets can be parallel or antiparallel.Slide8Slide9
Tertiary 3º Structure
This involves the folding of the polypeptide chains to give a more complex 3D structure.
The complexity of the tertiary structure of proteins has been determined using techniques such as X ray crystallography and NMR (nuclear magnetic resonance).
The tertiary structure is all about the interactions between the R groups.Slide10
Hydrophobic Interactions
The non-polar R groups (remember – these are hydrophobic) tend to get placed in the centre of the molecule.Slide11
Disulphide Bonds
Disulphide bonds are strong covalent bonds can form between - SH groups that are found in different parts of the polypeptide.
Think?
Which amino acid residue contains an –SH group?
Cysteine!Slide12
Disulphide bondsSlide13
Prosthetic Groups
Some proteins have associated non-protein groups. These are known as
prosthetic groups
.
Prosthetic Group
Name of Proteins
haeme
Myoglobin, haemoglobin
carbohydrate
glycoprotein
lipid
lipoprotein
nucleic acid
nucleoproteinSlide14
Myoglobin
Myoglobin has m –helices linked together with
nonhelical
sections. It contains a
haeme
group that is protected in a hydrophobic ‘pocket’.Slide15Slide16Slide17Slide18
Stability of Tertiary Structure
Protein structures are secured by weak hydrogen bonds and a few disulphide bonds.
Despite this they are surprisingly stable structures. This due in the most part to the evolution of proteins that have useful yet stable conformations.
Proteins fold to give a structure with the
lowest free
e
nergy
– this will therefore change if the chemical environment changes.Slide19
Quaternary 4° Structure
Some proteins are made up of 2 or more polypeptide subunits.
Haemoglobin is an example of a protein with a quaternary structure – it is
tetrameric
(made up of 4 parts). It has 2
α
–helices and 2
β
–sheets.
Each of the polypeptide chains has a
haeme group and the 4 chains are held together by hydrogen and ionic bonds. Slide20
HaemoglobinSlide21
Motifs and Domains
When describing proteins we can identify motifs and domains in the protein.
Motif – a particular form of secondary structure. An examples include
βαβ
motif or
β
barrel.
Domains – regions of a polypeptide chain that fold independently to give distinct regions with potentially different rolesSlide22
MotifSlide23
Domain
“A
protein domain
is a conserved part of a given protein sequence and
structure
that can
evolve
, function, and exist independently of the rest of the protein chain. Each domain forms a compact three-dimensional structure and often can be independently stable and
folded
.” Wikipedia
Pyruvate kinase has 3 different domains.Slide24
Classes and Functions of Proteins
Page 38 in your monograph details 9 different classes of proteins.
Your task:
Prepare a
powerpoint
, poster or
mindmap
to include all of the information found on page 38.
Try to come up with ways of
r
emembering the functions and some examples of each.
There will be a quiz on all of section 2.3 Proteins on
Monday November 26th
.Slide25
Your Task- Proteins
Past Paper Questions
You will need to access these in the department. Please
DO NOT TAKE
past papers home – we have limited numbers.
2002 MC Q5
2004 MC Q12
2006 Section B Q1
2008 MC 5
2009
Section B Q6
2. Complete Scholar activities on amino acids.3. Read and make notes on pages 30-35Make sure your glossary is up to date.
Pg 38 protein task.DUE Monday(November 26
th)