SCIE1106 Study Guide - Final Guide: Inverted Repeat, Ribosomal Rna, Inosine
TOPIC TWO: DNA to Proteins, the Central Dogma
DNA Structure:
DNA is the genetic material of a cell; a base-paired,
anti-parallel, right-handed double helix which code
for individual amino acids, the building blocks of
proteins. The building blocks of DNA are called
nucleotides, and consist of a phosphate group,
deoxyribose sugar and a base of adenine, thymine,
guanine or cytosine. Nucleotides are added together
through phosphodiester bonds where the
phosphate of one molecule reacts with the O( group
of another nucleotide.
If a sugar is deoxyribose (DNA), add a deoxy- prefix to the name (e.g.
deoxyadenosine) and if a sugar is ribose (RNA), the prefix ribo- is added to the
name (e.g. riboadenosine triphosphate). In general, adenine pairs with
thymine with 2 hydrogen bonds connecting them, and cytosine and guanine
pair together with three hydrogen bonds. Three bases together form one
codon, which codes for one amino acid.
DNA strands run in opposite direction (i.e. they are antiparallel). The strands are
complementary, with the sequence of one strand defining the sequence of the
other strand from base pairing rules. The information encoded by the order of
bases runs from 5’ to 3’. One strand is labeled the coding strand, while the other
strand is called the non-coding, or template strand.
DNA Replication:
Base
Abbrev
Sugar and base
(nucleoside)
Sugar, base and
phosphate (nucleotide)
Adenine
A
Adenosine
Adenosine monophosphate
Guanine
G
Guanosine
Guanosine monophosphate
Cytosine
C
Cytidine
Cytidine monophosphate
Thymine
T
Thymidine
Thymidine monophosphate
Uracil
U
Uridine
Uridine monophosphate
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There are a number of general features that apply to all chromosomal
replication:
1. Complementary base-pairing enables semiconservative DNA replication
2. DNA synthesis initiates at origins
3. Synthesis usually moves bidirectionally away from an origin via two
replication forks
4. Synthesis of new DNA is always -
5. Synthesis of new DNA requires a primer
Each strand of a double stranded DNA (dsDNA) molecule serves as a template for
synthesis of a new complementary strand due to the base-pair rules (A binding
to T, G binding to C). Each strand of a dsDNA molecule serves as a template for
synthesis of a new complementary strand. That means that each daughter
molecules has a parental strand plus a new strand. This provides more accuracy
and speed to the DNA replication process.
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dsDNA is pried apart at a replication origin by DNA helicase at a position
identified by a particular DNA sequence (called the ori). A group of proteins meet
to operate as a protein machine moving along a replication fork. DNA
polymerase adds nucleotides to the end of the new strand, and also has a
proofreading property to reduce error rate. Long linear chromosomes of
eukaryotes have multiple origins of replication whereas short, circular
chromosomes of prokaryotes have a single origin of replication.
Both daughter strands are polymerized in a to direction. The leading strand
is synthesized continuously while the lagging strand is synthesized
discontinuously, made up of a series of short Okazaki fragments.
There are a number of primers used in the DNA replication process:
• DNA primase (or RNA polymerase), which is used to synthesize short
strands of RNA on a DNA template.
• DNA polymerase, which adds each deoxynucleotide to the end of a
primer strand attached to the template strand.
• DNA ligase, which joins fragments by their sugar-phosphate backbones
The proteins at a replication fork cooperate to form a replication machine,
carrying out the following process:
1. Single stranded DNA (ssDNA)
binding proteins stabilize the
ssDNA and aid helicase
2. Helicase pries apart (unwinds) the
double helix to form another ssDNA
for replication
3. Sliding clamp holds DNA
polymerase firmly on the DNA
during DNA replication
4. Clamp loaded assembles the clamp
on the DNA using ATP energy
5. Lagging strand of DNA is folded to bring its DNA polymerase into a
complex with the leading strand DNA polymerase
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Document Summary
Topic two: dna to proteins, the central dogma. Dna is the genetic material of a cell; a base-paired, anti-parallel, right-handed double helix which code for individual amino acids, the building blocks of proteins. The building blocks of dna are called nucleotides, and consist of a phosphate group, deoxyribose sugar and a base of adenine, thymine, guanine or cytosine. Nucleotides are added together through phosphodiester bonds where the (cid:887)(cid:495) phosphate of one molecule reacts with the (cid:885)(cid:495) o( group of another nucleotide. If a sugar is deoxyribose (dna), add a deoxy- prefix to the name (e. g. deoxyadenosine) and if a sugar is ribose (rna), the prefix ribo- is added to the name (e. g. riboadenosine triphosphate). In general, adenine pairs with thymine with 2 hydrogen bonds connecting them, and cytosine and guanine pair together with three hydrogen bonds. Three bases together form one codon, which codes for one amino acid. Dna strands run in opposite direction (i. e. they are antiparallel).
