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Learning Outcomes:
 Describe how DNA and RNA encode for the amino
acid sequence in a polypeptide chain.
 Describe the structure of DNA and RNA in terms of a
sugar–phosphate backbone and attached bases.
Storyline EP2 (p 144 to 149) Activities EP2.7 and EP2.8.
 Explain the role of hydrogen bonding in the pairing
of bases in DNA, and the replication of genetic
information by RNA.
 Illustrate and explain the role of hydrogen bonds as
intermolecular forces, which help determine the
sequence of amino acids in a polypeptide chain.
Chemical Ideas: Chapter 5.4 (p 102 to 108)
Cell structure
cytoplasm
~ gel of molecules
Rough endoplasmic
reticulum
~ protein synthesis
Nucleus
DNA ~ genetic material
Ribosomes
~ protein synthesis
DNA ~ genetic information and the blue print for
protein synthesis
Bases in DNA:
 Thymine T
 Cytosine C
 Adenine A
 Guanine G
Hydrogen bonds
between
base pairs
Part of a DNA strand- a gene – unzips and
transcription of the base pairs produces a strand of
mRNA.
RNA ~ Ribonucleric acid in a cell
Nucleus (DNA)
tRNA
collect amino acids in the
cell’s cytoplasm and carry
them to the ribosomes
where they will be built into
a polypeptide chain ~
translation
1 gene 1 polypeptide chain
Transcription
DNA used as a
blue print to
make mRNA
mRNA carries the
code for protein
synthesis and goes to
ribosomes.
Bases carried on the DNA strands code for an
amino acid sequence that will form a protein.
Bases in DNA:
Bases in RNA:
 Thymine T
 Uracil
 Cytosine C
 Cytosine C
 Adenine A
 Adenine A
 Guanine G
 Guanine G
U
How bases pair to form mRNA:
Adenine
A
Uracil
U
Cytosine
C
Guanine
G
Thymine
T
Adenine
A
Guanine
G
Cytosine
C
Three bases ~ tripet base codes, or codons, are
used for each amino acid.
in this example it would
bind to GCC, the codon
for alanine
Anti-codon for binding
to a codon on mRNA:
mRNA from the nucleus
sugar phosphate molecule
base
Bases that make up the triplet base
codons are attached to sugar
phosphate molecules, which together
are called RNA
Chemical composition of Ribonucleric Acid
Ribose sugar molecules ~ C5H10O5
Phosphate groups H2PO4
One of 4 bases: A,U,G or C
H
OH
O
A unit of RNA
H2O
BASE
O
H2O
O
phosphate
Representations of the structure of RNA
How an ester bond is formed between the tRNA and
an alanine molecule:
an ester
link
CH3
CH3
H2N - C - COOH
H2 N - C - C = O
alanine
H
molecule
one tRNA
H
+ H2O
When a tRNA collects an amino acid it takes it to
the mRNA strand that has become attached to a
ribosome.
Protein synthesis: ribosome read codons on mRNA.
Ribosome moles along the mRNA chain
Amino acids bond into
the polypeptide chain
tRNA molecules
bring amino acids
to the mRNA in the
ribosome
H2N
COOH
tRNA leave the
ribosome when it
has delivered its
amino acid
The bases in RNA are planar and the bases fit
together so that groups are in just the right
positions for hydrogen bonds to form ~ molecular
recognition.
2 hydrogen bonds between uracil and adenine
3 hydrogen bonds between cytocine and guanine
Read in Chemical Storylines:
EP2 Protein building pages 140 to 149
Make your own
summary notes/annotated diagrams
about how amino acids are converted into
polypeptide chains inside cells