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

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