The Four Levels of Protein Structure: a level biology


hey guys welcome back to learnbiology.net I’m Frankie and in this revision session will cover specification
reference three point one point four point one this is topic 1a and your
learning outcomes are number one understand the four levels of protein
structure number two understand the roles played by different bonds such as
hydrogen bonds ionic bonds and disulfide bridges in the structure of proteins a
linear sequence of many thousands of amino acids builds large complex
macromolecules known as proteins proteins are fundamental molecules and
with the diversity of structures and functions are an essential component of
all living organisms protein typically makes up approximately 50 percent dry
weight of most cells and are therefore essential players in almost every
cellular process functional proteins are dependent upon the three-dimensional
conformational shapes its tertiary structure this unique configuration or
arrangement of the amino acids from the primary structure will determine the
biological function that a particular protein plays if in some way for example
mutation or denaturation the proteins primary structure is changed then its
tertiary structure is affected often rendering the protein useless let’s take
a look at the four levels of protein structure these sequential levels help
us understand how a proteins three-dimensional conformational shape
is determined firstly a specific linear sequence of amino acids is constructed
which we will cover in more detail when we learn about transcription and
translation in topic for a this linear sequence of amino acids is known as the
primary structure of the protein commonly called a polypeptide chain with
one end of the chain having the amine group the nh-2 and the other having the
carboxyl group of the seed of low h remember each amino acid is connected by
a peptide bond the amino acids here represented by those blocks and the line
that joins them represents each of those peptide bonds next we have the proteins
secondary structure here the polypeptide chain folds and coils into specific
structures known as number one the alpha helix and the Alpha helix is essentially
a coiled section of the polypeptide chain and number two we have a beta
pleated sheet which is a folded section of the polypeptide chain notice there on
each of these the Alpha helix and the beta pleated sheet we have hydrogen
bonds represented as these dotted blue lines which form to hold the secondary
structures together so the hydrogen bonds are shown here on the Alpha helix
and between parallel polypeptide chains of the beta pleated sheets in diagrams
in many textbooks for example beta pleated sheets are often represented as
flat arrows like this and so to reiterate the secondary structures of
proteins let’s see how both the Alpha helix and beta pleated sheets may be
represented together in a typical schematic diagram and here we see the
Alpha helix represented as a coil and there’s another alpha helix whilst the
beta pleated she is shown here are depicted as these flat arrows on this
diagram we can also make out the amino acids which are linked together by
peptide bonds and finally we have these dotted blue lines representing the
hydrogen bonds which form between the R groups of specific amino acids holding
the secondary structures together and there we are
the hydrogen bonds between the coils of the alpha helixes and the hydrogen bonds
between the beta pleated sheets as the polypeptide folds and coiled further the
tertiary level of protein structure is formed here a number of different bonds
are formed between specific R groups of the certain amino acids the bonds you
need to know are number one in bonds number two ionic bonds and
number three disulfide bridges hydrogen bonds and ionic bonds are formed between
positively and negatively charged our groups of the amino acids while some
amino acids have cysteine in there are groups which contains sulfur and when
these atoms bond a strong covalent bond called a disulfide bridge is formed now
held together by a variety of these bonds the tertiary structure of the
protein can be defined resulting in the proteins three-dimensional
conformational shape and for many proteins this is its final level of
protein structure however many proteins are a combination of one or more
tertiary level polypeptides assembled together and connected via further
bonding associations for these quaternary level proteins their final
three-dimensional conformational shapes are only realized once all relevant
polypeptide chains are connected the quaternary level structures of proteins
such as hemoglobin insulin and collagen are key examples and that brings us to
the end of another revision session in the next one we’re going to take a look
at protein shape and function so until then as always take it easy

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