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Central Dogma, Triplet Code and Wobble Pairing
Understanding Genetics: The Central Dogma
In the next few videos, we will be discussing the genetic code
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Ribosomes are responsible for translating mRNA into proteins
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Wobble Pairing
The basis for redundancy is the concept of wobble pairing
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For some amino acids, two codons are used
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It means that it can bind to more than one base pair
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Inosine is a modified
nitrogenous base that occurs in tRNAs
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Once RNA polymerase binds, it needs to unwind DNA in order to use it as a template to create
RNA
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Unlike DNA polymerases, RNA polymerases do not have proofreading activity
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The one exception is that DNA contains thymine and RNA contains uracil
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RNA splicing is the process of
removing noncoding introns
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The spliceosome, consisting of RNA-protein complexes called
small nuclear ribonucleoproteins (snRNPs), binds to pre-mRNA and performs the splicing
process
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Nucleosides
MedSchoolCoach MCAT Prep
Nucleic acids include pentose sugars with five carbon atoms
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Nitrogenous bases,
purines and pyrimidines, are separated by their ring structures
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Furthermore,
nucleotides are essential as an energy source for many metabolic processes
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The Watson
Crick base pairing can be applied not only for DNA but also for RNA
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This model
was important as it explained a simple mechanism for DNA replication
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Guanine in one DNA molecule pairs with cytosine in the other DNA molecule
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The Northern blot technique is used to detect the presence of a particular RNA molecule
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The image below shows a diagram of the Northern blot
technique
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Without telomerase, DNA replication would cause the ends of the chromosomes,

known as telomeres, to shorten with each round of division
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Telomeres are regions of repetitive DNA sequences located at the ends of chromosomes
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Think of them as
the aglets on the ends of your shoelaces that prevent fraying
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Telomerase binds to the overhang of the shortened telomere and extends it using its RNA
sequence
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By adding more repetitive sequences to the
end, telomerase can maintain or even increase the length of a telomere
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Chromosomal Proteins, Chromosome Organization and
Single Copy vs
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Chromosomal Proteins
There are many different types of proteins associated with chromosomes, but the one you need
to know is called Histones
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It
contains the majority of coding sequences
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It is possible for mutations to accumulate in these areas without
producing deleterious effects
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The operons can be regulated in two ways: negative control or positive
control
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In the presence of lactose, lactose will actually bind to the repressor, preventing it
from binding to the operator
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However, in the presence of lactose, it actually binds to lactose

Operon/Jacob-Monod Model Part 2
Positive Control of Operons
In positive control of operons, an activator protein binds to the DNA to stimulate transcription
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When an inducible
molecule binds to an activator protein, it causes a conformational change that will either allow
or prevent the protein from binding to DNA
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This is different from prokaryotes, where each RNA can

encode for multiple protein products
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This allows different cells to express different combinations of
proteins more easily
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Alternative splicing refers to the fact that different
combinations of introns and exons can be kept or removed in a pre-mRNA molecule
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miRNAs are one way of silencing gene expression
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In prokaryotes, ribosomes bind to a specific sequence of
nucleotides just before the start codon
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There are three different sites in the ribosome called the A site, P site, and E
site
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The A site is where the new tRNA with amino acid binds
The P site is where the growing peptide chain is held
The E site is where the empty tRNA exits

It is important to note that there are no tRNAs with an anticodon that matches the three stop
codons that do not encode for a tRNA
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These modifications can occur along many places in a protein including the N-terminus or the
side chains of the amino acids
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Acetylation
Acetylation involves the addition of an acetyl group for the MCAT
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DNA Methylation
DNA methylation is the addition of a methylated DNA to bind to the histone less tightly
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Glycosylation
Glycosylation involves the addition of carbohydrate to a protein
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Disulfide Bonds
Disulfide bonds are a covalent modification and are important for stabilizing protein structure
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