BTEC Level 3 National Applied Science, Student Book
This is Btec Applied Science Unit 11 Assignment A (Structure and function of nucleic acids) which was awarded a distinction. This is an example of a Distinction level assignment, and you may use it as a guide to help you achieve a distinction and finish this assignment.
Unit 11: Genetics and Genetic Engineering
A: Understand the structure and function of nucleic acids in order to describe gene expression and the
process of protein synthesis
Assignment title: Structure and function of nucleic acids
Nucleic Acids: Nucleic acids, biopolymers
required for gene delivery, encoding, and
expression, are found in all organisms. Because
they were originally found in the cell nucleus,
these important molecules that are also found
in bacteria, viruses, mitochondria, and
chloroplasts are called nucleic acids. The two
main categories of nucleic acids are ribonucleic
acids and deoxyribonucleic acids ( DNA)
(RNA). Nucleotide monomers joined together https://www.thoughtco.com/thmb/YQ6-4kkDuO_9f2Ga8SPVRZuIbxs=/1500x0/
form the building blocks of nucleic acids. filters:no_upscale():max_bytes(150000):strip_icc():format(webp)/nucleotide_base-
5b6335bdc9e77c002570743e.jpg
Nitrogenous bases, pentose sugars (pentoses),
and phosphate groups are the three components that make up nucleotides. Nitrogenous bases are
composed of pyrimidine and purine molecules (adenine and guanine) (cytosine, thymine, uracil). Both
RNA and DNA include deoxyribose, a pentose sugar with five carbons. Nucleotides are joined to create
polynucleotide chains. They are joined by a covalent link between a sugar and phosphate on each side.
These linkages are referred to as phosphodiester links. Phosphodiester linkages make up the sugar-
phosphate backbone of both DNA and RNA. Dehydration synthesis, which also happens in proteins and
carbohydrate monomers, is used to link nucleotides together. When nitrogenous bases are added, water
molecules are lost during the synthesis of nucleic acids. The finest illustration of how certain nucleotides
may carry out crucial cellular functions as "single" molecules is adenosine triphosphate (ATP), which
drives several cellular activities.
DNA: DNA is a double-stranded molecule, organized into
chromosomes and located in the cell nucleus. DNA encodes
the genetic material of an organism. Two helical strands of
nucleic acid are twisted into a double helix, creating double-
stranded DNA. This twist makes the DNA more compact.
DNA fits into the nucleus by being tightly wrapped around a
component called chromatin. Chromosomes are formed
when chromatin condenses during cell division. Chromatin
relaxes to allow the cellular replication machinery to access
the DNA strands prior to DNA replication. DNA is also found
in mitochondria and chloroplasts, but chromosomes are
https://1.bp.blogspot.com/-zdmE6r1xKE0/XdgSLd0u-bI/AAAAAAAAdVk/JKI5u
found only in eukaryotic nuclei. Prokaryotes, which lack a oRJUgP3VBVgAuauKNImIfFgCNcBGAsYHQ/s1600/DNA.png
,nucleus that is attached to a membrane, contain one circular chromosome of DNA in their cytoplasm.
Extrachromosomal DNA, sometimes known as a plasmid, is a kind of self-replicating genetic material
that is present in some prokaryotes, including bacteria, and some eukaryotes. In order to analyse gene
expression, recombinant DNA methods frequently employ plasmids. When cells divide, copies of this
genetic data are passed on to new cells. When replicating, the genetic code is copied. Replication is
accomplished by many mechanisms, including replication enzymes and many proteins called RNAs.
Eukaryotic cells, including animal and plant cells, replicate DNA during the mid-S phase of the cell cycle.
DNA replication is required for the growth, repair, and regeneration of living cells.
Stages of DNA replication:
Step 1: Replication Fork Formation: A double-stranded DNA molecule must be "unzipped" into two
single strands before it can replicate. The two DNA strands are held together by four DNA bases:
adenine (A), thymine (T), cytosine (C), and guanine (G). Cytosine and adenine or guanine do not
combine. Only thymine. These base pair bonds must be broken in order for the DNA to unwind. DNA
helicase is the enzyme responsible for this. DNA helicases break base-pair hydrogen bonds, splitting the
base strand into replication fork-like structures. From here the replication process begins. Each strand of
DNA has aligned 5' and 3' ends. This symbol represents a side group attached to the DNA backbone. The
3' end has a hydroxyl group (OH) and the 5' end has a phosphate group (P). This orientation is important
as replication can only occur in the 5' to 3' direction. However, replication forks are bi-directional. The
leading strands are oriented 3:5, while the tail strands are oriented 5:3 (lagging strands). As a result, he
replicates the two planes using his two different processes that allow different directions.
Step 2: Primer Binding: Duplicating the main strand is
easy. After the DNA strands are separated, the 3' ends
of the DNA strands are attached to short pieces of RNA
, called primers. Primer binding always indicates that replication has begun. Primers are generated by the
enzyme DNA primase.
Step 3: Elongation: The process of elongating or joining additional strands is carried out by DNA
polymerase enzymes. There are five major variants of DNA polymerases in both bacterial and human
cells. Polymerases I, II, IV, and V are involved in error detection and repair in bacteria such as E. coli,
while polymerase III functions as the key enzyme
involved in replication. During replication, DNA
polymerase III attaches to the primed strand and
begins adding new base pairs complementary to the
strand. The three major polymerases involved in
eukaryotic DNA replication are alpha, delta, and
epsilon. Replication occurs in the 5' to 3' direction on
the leading strand, so the newly generated strand is
contiguous. Replication is initiated by the lagging
strand by binding a number of primers. Each primer
https://bam.files.bbci.co.uk/bam/live/content/zgg2n39/large
is separated by just a few bases. Okazaki fragments
are then added to the strand between the primers by a DNA polymerase. Fragmentation of newly
created fragments stops this replication process.
Step 4: Termination: After creating both continuous and discontinuous strands, the enzyme exonuclease
removes the RNA primer from the first strand. Then replace these primers with the required bases. The
newly generated DNA is examined for errors, corrected, and replaced with another exonuclease. A DNA
ligase enzyme joins the Okazaki fragments into one continuous strand. Their linear DNA ends pose a
problem because DNA polymerases can only add nucleotides in the 5' to 3' direction. At the ends of the
parental strand are repeated sequences of DNA called telomeres. Telomeres, which act as protective
caps that prevent adjacent chromosomes from joining together, are structures found at the ends of
chromosomes. Telomerase is a special type of DNA polymerase enzyme that catalyses the synthesis of
telomere sequences at DNA ends. Ultimately, a recognizable double helix is formed by the
complementary and paternal DNA strands. At the end of the process, two DNA molecules are formed.
Each consists of the original strand and a new strand from the first molecule.
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