Download B8. Nucleic Acids (HL)

B8. Nucleic Acids (HL)
Nucleic Acids
• Natural polymers built from monomers
known as nucleotides.
• Nucleic acids usually contain thousands
of nucleotides and are among the largest
macromolecules found in the body.
• Two types: Deoxyribonucleic Acid and
Ribonucleic Acid
• Nucleotides are made up of three parts
– A phosphate group
– A pentose sugar
– A nitrogenous base
- The phosphate group attached to the 5-prime
carbon and a nitrogenous base is attached to
the 1-carbon
A nucleotide
A numbered ribose
Formation of Polynucleotides
• Polynucleotides are formed when one or more
nucleotides are bonded together.
• Nucleotide triphosphates (unbonded nucleotides with
three phosphate groups) attach to the 3-prime carbon on
the DNA backbone. The energy for this reaction is
provided by the hydrolysis of the bonds between the
phosphate groups.
Deoxyribonucleic Acid
• But, the nitrogenous bases of complementary strands are
bonded by hydrogen bonds
– There are 2 bonds between thymine and adenine
– There are 3 bonds between cytosine and guanine
• There are two strands in a DNA double helix, running in antiparallel fashion
– Hydrogen bonds hold the strands together due to the side chains
present
●
Deoxyribose lacks an oxygen atom on C2.
●
DNA is a doubled strand nucleic acid.
• Uses of DNA:
– Storage of genetic information
– Allows living organisms to reproduce
– Coordinates, with RNA, the process of protein synthesis
• DNA is composed of:
– A phosphate group
– Ribose (as the sugar)
– The organic nitrogenous bases: Adenine, Guanine, Thymine, and
Cytosine
• Adenine and Guanine are purines
• Cytosine and Thymine are pyrimidines
• The phosphate and ribose in the DNA make up its backbone
and are bonded together by covalent phosphodiester bonds
• The sugar and nitrogenous bases are also bonded together
by covalent bonds
●
Nitrogenous bases are specific in their pairing and one DNA
strand determines the arrangement of the complimentary
strand
Bonding of Nitrogenous Bases
Types of Ribonucleic Acid (RNA)
• There are three types of RNA molecules involved
in the processes that we are studying
– Messenger RNA (mRNA)
– Ribosomal RNA (rRNA)
– Transport RNA (tRNA)
Ribonucleic Acid (RNA)
• RNA consists of a very similar structure to DNA
except for these key differences:
– Uracil replaces thymine
– Ribose replaces deoxyribose
(pentose; lacks an oxygen on the
second carbon atom)
– RNA is single stranded
Comparative structures of uracil
and thymine: thymine has an
extra methyl group
Comparitive structures of
ribose and pentose
Protein Synthesis
• Chromosomes are very long DNA sequence which
store genetic information
– there are 23 pairs of (different) chromosomes in
the human body
• A gene is a finite anddiscrete unit of heredity that is
coded by a sequence of nitrogenous bases
• Through a series of processes (transcription and
translation), the nitrogenous bases will come to
dictate a series of amino acids
– These amino acids will form a polypeptide which
will in turn form a protein : GENE TO PROTEIN
• Proteins directly or indirectly determine the
observable characteristics of an individual
Transcription
• In this process, the DNA helix is unwinded (with
the help of the enzyme helicase) and a
complimentary strand of RNA is formed
– This RNA is known as mRNA
• The mRNA undergoes editing processes until a
specific sequence of bases is achieved
• The mRNA exits the cell’s nucleus and enters the
cell’s cytoplasm
Translation
• Once the mRNA exits the nucleus and enters the cell’s
cytoplasm, it is directed to the ribosome- also known as rRNA
• Each triplet of base pairs are referred to as a codon while
each codon corresponds to a specific amino acid
– This is known as the genetic code and it is both universal
and degenerate
• These amino acids will be brought to the ribosome by tRNA
and the formation of a polypeptide will commence
• Once the specific protein is formed, the mRNA, rRNA, and
tRNA will separate
• The polypeptide sequence will undergo further conformational
changes in order to become a functioning protein
DNA Profiling
•
All individuals have variations in their genetic information
•
Certain sequences are repeated throughout a gene while the length of each
sequence determines the individuality
•
When a DNA sample is gathered as evidence, restriction enzymes are used to
cut the sample into a specific coding sequence that matches the coding
sequence that will be compared
•
These sequences are known as microsatellites and there are certain splits
that occur in each sample (regions where there are no codons) that are
specific to each individual
Gel Electrophoresis
•
The samples are placed into wells cast in a gel
•
The gel is immersed in a conducting fluid and an electric field is applied
•
Sample will move across the gel a certain distance depending on its size
•
The bands obtained are then labeled with radioactive phosphorus
•
X-ray film is used to detect radiation and a fingerprint is obtained
•
This fingerprint is then used for comparison purposes such as paternity cases,
criminal cases, and to map evolutionary traits of species
•
There is a slight chance of error with this process as individual gene sections
may match – because we are dealing with such a small region