Name: _________________________________________ Class: _________ Date: _________________________
Topic 7: AHL : Nucleic Acids and Proteins : 7.5: Proteins
(Matches up with CORE 3.2)
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Proteins are essential parts of organisms and participate in virtually every process within cells.
They are large biological molecules consisting of one or more chains of ____________________________.
Proteins perform many functions including: ________________________________________________________________________
______________________________________________________________________________________________
Proteins differ from one another primarily in their ___________________ of amino acids, which is dictated by
the nucleotide sequence of their genes. This results in ______________________of the protein into a specific threedimensional structure that determines its activity.
By folding into distinct shapes, proteins can perform very different roles despite being composed of the same basic
building blocks. To draw an analogy, all vehicles are made from steel, but a racecar’s sleek shape wins races, while
a bus, dump truck, crane, zamboni are each shaped to perform their own unique tasks.
PROTEIN STRUCTURE cont’d
There are _____ levels of structure to a protein. These levels of structure are referred to as:
1)
___________________________ structure
2)
___________________________ structure
3)
___________________________ structure
4)
___________________________ structure
Primary Structure
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Refers simply to the ___________________ of ______________________.
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Because there are __________ amino acids, there are countless possibilities for different primary structures.
Secondary Structure
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As the molecule begins to form, the molecule begins to __________________
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It usually forms into a spring-like shape called an _______________________
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This spring shape is maintained by _______________ bonds between every fourth amino acid.
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The other option is that it forms into a ______________________________
Tertiary Structure
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The tertiary structure is the complex, ______ protein shape
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Most proteins fold into this unique 3-dimensional structures
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It is the _________________ and _________________ of the alpha-helix and Beta-pleated sheet.
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As the “spring” or “sheet” (secondary structure) gets longer, some kinks appear.
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The folding of the polypeptide is due to ___________________________________________________________
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These bonds include __________________________________________________________________________
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A disulphide linkage depends on the presence of the amino acids _________________, which contains _________.
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An electrovalent bond can form between the negatively and positively charged molecules or amino acid groups
along the chain.
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The main types of tertiary structure of proteins are the ______________ proteins and the _____________ proteins
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Examples of Tertiary Proteins: ___________________(an iron- and oxygen-binding protein found in muscle tissue
of vertebrates), _______________________________________________
Quaternary Structure
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The quaternary structure is the hierarchical level for appreciating the _______________ and __________________
proteins, consisting of the two or more sub-units.
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When different ____________________________ come together
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The structure formed by several protein molecules (polypeptide
chains), usually called protein subunits, which function as a single
protein complex.
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Quaternary structure may also involve the binding of a prosthetic
group (like iron in hemoglobin and Mg in chlorophyll) to form a
conjugated protein.
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Example of a Quaternary Protein: ____________________ - whose quaternary structure consists of four tertiary
subunits with central HEME (IRON) containing components, ________________________________ (ANTIBODIES),
and _____________________.
Classes of Proteins (according to shape and solubility):
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Proteins can be divided into 3 classes: _______________________________________________________________
Fibrous Proteins
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________________ proteins
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__________________________________________________
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Fibrous proteins are best understood in terms of their stable,
repetitive secondary structures, which could be in the alpha
helix or beta pleated form.
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Two examples of fibrous proteins are: _______________ (in hair
and skin) and ___________________ (in tendons, cartilage, and
bones).
Globular Proteins
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The ________________________________ class of proteins
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Have a ________________ structure and are water soluble
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Some are _________________ and others are ________________________.
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Folded into three-dimensional shape - with a ___________________ interior and ___________________ exterior.
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Examples of globular proteins: _________________, ___________________, and ____________________
_____________________, _________________
Membrane Proteins
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Serve as protein channels, carriers, receptors, or as cell identification.
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Some are tertiary proteins and others are quaternary.
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______________ amino acids have ________________
(neutrally charged) R groups.
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____________ amino acids have R chains with _________
groups (charged either positive or negative).
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Proteins with a lot of polar amino acids make the proteins
______________ and therefore able to interact with water.
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Proteins with many non-polar amino acids are more
_______________ and are less soluble in water.
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With these characteristics, proteins tend to fold themselves so that the hydrophilic ones are on the inner side. This
is important for protein channels running through membranes.
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Hydrophilic molecules and ions are to pass in and out of the cells easily through these hydrophilic channels.
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The hydrophobic edges of the channels align with the fatty acid chains of phospholipids, which help control the
stable positioning of the channels.
Denaturing Protein
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The weaker bonds (eg. Hydrogen bonds) of the tertiary structure are easily broken.
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Such
factors
as
___________________
changes,
_____________
changes,
or
the
presence
of
_______________________________ ions can cause the hydrogen bonds to break, making the protein lose its
tertiary shape. Such a protein would be called __________________.
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As the _______________ of the protein depends on its shape, a denatured protein cannot function normally (this is
especially true in the case of enzymes)
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For example, when milk sours, the protein _____________ denatures and forms insoluble floating lumps.
End of Protein Notes
To Do for Review
1) Explain the four levels of protein structure, indicating the significance of each level. (7.5.1)
2) Outline the difference between fibrous and globular proteins, and give two examples of each protein type (7.5.2)
3) Explain the significance of polar and non-polar amino acids. (7.5.3)
4) State four functions of proteins, giving a named example of each. (7.5.4)