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
Rough endoplasmic reticulum
~ protein synthesisNucleus
DNA ~ genetic materialRibosomes
~ protein synthesis
cytoplasm
~ gel of molecules
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.
Nucleus (DNA)
Transcription DNA used as a blue print
to make mRNA
1 gene 1 polypeptide chain
mRNA carries the code for protein
synthesis and goes to ribosomes.
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
RNA ~ Ribonucleric acid in a cell
Bases in DNA:
Thymine T
Cytosine C
Adenine A
Guanine G
Bases carried on the DNA strands code for an amino acid sequence that will form a
protein.Bases in RNA:
Uracil U
Cytosine C
Adenine A
Guanine GHow bases pair to form
mRNA:
Adenine A UracilU
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.
mRNA from the nucleus
Anti-codon for binding to a codon on mRNA:
in this example it would bind to GCC, the codon for alanine
Bases that make up the triplet base codons are attached to sugar phosphate molecules,
which together are called RNA
sugar phosphate molecule
base
Chemical composition of Ribonucleric Acid
Ribose sugar molecules ~ C5H10O5
Phosphate groups H2PO4
One of 4 bases: A,U,G or C
A unit of RNA
H
O
O
O
BASE
phosphate
H2O
H2OOH
Representations of the structure of RNA
one tRNA
- C -
H2
N
COOH
CH3
H
- C -
H2
N
C = O
CH3
H
How an ester bond is formed between the tRNA and an alanine molecule:
alanine molecule
an ester link
+ 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
tRNA molecules bring amino acids to the mRNA in the ribosome
tRNA leave the ribosome when it has delivered its amino acid
Amino acids bond into the polypeptide chain
H2N
COOH
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
Make your own
summary notes/annotated diagrams about how amino acids are
converted into polypeptide chains inside cells
EP2 Protein building pages 140 to 149
Read in Chemical Storylines: