Seniors Tuition And Mentorship Program Semester

Seniors’ Tuition And Mentorship Program (Semester 2, 2014)
Year 2

2.24: DNA notes
Central Dogma of Molecular Biology

DNA
-DNA is better known as deoxyribonucleic acid
-It is made up of small subunits known as nucleotides.
-These nucleotides are further made up of a phosphate group, a deoxyribose sugar and a nitrogenous base.

-DNA usually exists as a double-helix structure that is made up of 2 polynucleotide strands that run antiparallel to each other
-These two polynucleotide strands are held together by interactions between the nitrogenous bases.
These interactions are known as hydrogen bonds.
-There are 4 nitrogenous bases in DNA. They are Adenine, Thymine, Guanine and Cytosine.

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2.24: DNA notes
-Nitrogenous bases only interact with certain nitrogenous bases. For instance, Adenine interacts with Thymine, while Cytosine interacts with Guanine.

RNA
-RNA, also known as ribonucleic acid, is single-stranded.
-An RNA nucleotide is structurally similar to that of a DNA nucleotide, but it contains a ribose sugar instead of a deoxyribose sugar.
-In addition, RNA has the nucleotides Adenine, Cytosine, Guanine and Uracil. Thymine is NOT present in RNA.
-Adenine pairs with Uracil, while Cytosine pairs with Guanine.
-RNA is usually used as a “temporary molecule”, meaning that it is usually made only when needed.

DNA Replication
-Begins in locations of genomes known as “origins”
-Replication starts with unwinding of the double-helix DNA at the origin by DNA helicase (an enzyme), and the synthesis of new strands creates a replication fork
-DNA polymerase synthesises new DNA by adding nucleotides matched to the template strand.
-The replication of DNA is also known as a semiconservative process, in which the original parent strands serves as the template for the new complimentary strands to be created.
-Replication is done in a 5’ to 3’ direction

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2.24: DNA notes

Protein Synthesis (Transcription and then translation)
-Only one DNA strand is used as the template strand for transcription
-RNA polymerase is used in creating copies of mRNA (messenger RNA) from the template strand.
This is a similar process to DNA polymerase replicating a copy of a DNA template strand by creating a new strand from stringing nucleotides that are complementary to the template strand.
-However, transcription is done in a 3’ to 5’ direction, which is in the opposite direction of DNA replication. -After transcription, the mRNA exits the nucleus and attaches itself to a ribosome, where tRNA will begin the translation process.
-Transfer RNA, better known as tRNA, translates mRNA into a protein molecule within the cytoplasm.
-tRNA contains anticodons that are complementary to codons on the mRNA. Each codon on the mRNA has a different complementary anticodon, hence it also specifies for a different amino acid.
-Each tRNA carries a specific amino acid, which joins together with the other amino acids to form a polypeptide chain after the mRNA has been read and translated.

-Proteins are built from amino acids linked up in a chain to form a 3D structure.

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2.24: DNA notes
-Almost all organisms use the same genetic code.
-In addition, each amino acid can be specified by more than one codon. (degenerate)

Recombinant DNA
-The process of recombination involves taking sections of an organisms DNA and fusing it with the
DNA of another organism into a single DNA molecule.
-The process begins with action by restriction enzymes. Restriction enzymes are able to recognise specific nucleotide sequences on a DNA molecule and cleaves the DNA at those sites.
-The DNA section cut by the restriction enzymes will have some single-stranded sections, known as sticky ends.
-The exposed nucleotides at the sticky ends will then undergo complementary base pairing with another organism’s DNA which has also been cleaved by the same restriction enzymes.

-After the organism’s DNA and foreign DNA have come together, DNA ligase repairs the sugar phosphate backbone.

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