• Chromosomes are found in the nucleus of the cell.

• Chromosomes are made of DNA.

• DNA = Deoxyribonucleic acid

• A DNA molecule has 2 strands.

• DNA strand made of nucleotides.

Nucleotide:

Deoxyribose sugar

Phosphate

Base

Nucleotides on the same strand are held together by a strong chemical bond. The bond forms between the sugar and phosphate. This is called the sugar-phosphate backbone.

Strong chemical bond.

4 different bases: Adenine (A), Thymine (T), Cytosine (C), and Guanine (G).

T A

GC

T A

GC

A and T join together, and G and C join together. They are complementary to each other.

Bases are held together by weak hydrogen bonds.

The resultant molecule is DNA.

The 2 strands twist together to form a double helix.

Fig. 3.3 p.19

RNA = ribonucleic acid.

Made of nucleotides of the same structure, joined in the same way.

3 differences from DNA : -

1. Uracil instead of thymine

2. Single-stranded

3. Ribose sugar instead of deoxyribose

2 types of RNA:

1.Messenger RNA (mRNA) – carries code for a gene from DNA to ribosome.

2. Transfer RNA (tRNA) – carries specific amino acids to growing protein.

For the following strands of DNA, write the complementary bases on the next DNA strand.

1.G A G A C A T T T A C G

2. C T T G C C A A T A C G

3. A G C T T G A C C A T G

C T C T G T A A A T G C

G A A C G G T T A T G C

T C G A A C T G G T A C

For the following strands of DNA, write down their complementary strands of RNA .

1. G A G A C A T T T A C G

2. C T T G C C A A T A C G

3. A G C T T G A C C A T G

C U C U G U A A A U G C

G A A C G G U U A U G C

U C G A A C U G G U A C

• chemical components of DNA same from species to species.

• sequence of bases unique

• bases make up genetic instructions which control inherited characteristics.

• DNA can reproduce itself exactly

• process called DNA replication

1.DNA helix unwinds.

2. Weak H bonds between bases break => 2 DNA strands separate with bases exposed.

Fig. 9.4 p.70

3. Free DNA nucleotides align with complementary nucleotides on open chain.

4. Weak H bonds form between complementary pairs.

5. Strong chemical bond forms between nucleotides to form a chain. Controlled by DNA polymerase.

6. Daughter DNA molecules wind back up into double helix.

http://www.lewport.wnyric.org/jwanamaker/animations/DNA%20Replication%20-%20long%20.html

Stick in simplified replication diagram.

For replication to occur, nucleus must contain:

1. DNA (for template)

2. Nucleotides

3. Enzyme

4. ATP (energy)

• 2 new molecules formed

• One new strand, one from parent molecule

=> semi-conservative

• replication allows new genetic information to be formed

• 2 DNA molecules coil up, and become 2 identical chromatids held by centromere.

• replication ensures exact copy of genetic information is passed from cell to cell.

• inherited characteristics are controlled by enzymes.

• enzymes are made of protein

• a protein’s function depends on correct sequence of amino acids

•Order of amino acids is controlled by base sequence of DNA.

=>DNA determines inherited characteristics.

• DNA carries the genetic code

• Each triplet of bases is called a codon

•Each codon codes for one amino acid.

Protein synthesis – 2 stages:

1. Transcription Fig. 3.6 p.21

2. Translation Fig. 3.8 p.22

This stage makes a copy of the DNA code to take to the ribosomes.

Copy = messenger RNA (mRNA)

*Fig. 3.6 p.21*

1. DNA strands unwind.

2. Weak H bonds break => DNA strands separate.

3. Free RNA nucleotides line up with complimentary bases on DNA.

4. Weak H bonds form between bases.

5. Strong chemical bonds form between RNA nucleotides. Controlled by RNA polymerase.

6. H bonds between RNA and DNA bases break => strands separate.

7. mRNA moves to cytoplasm, and attaches to a ribosome.

8. H bonds form between DNA bases, strand winds up into double helix.http://www.biostudio.com/d_%20Transcription.htm

Stick in simplified transcription diagram.

Each triplet of bases on mRNA = codon.

Transfer RNA (tRNA)

• each tRNA molecule has a triplet of bases => anticodon.

• each anticodon codes for one amino acid.

• each cell ~ 20 tRNA molecules (one per amino acid).

• tRNA transports amino acid to site of protein synthesis, and ensures amino acids align in correct order.

1. Ribosome attaches to one end of mRNA.

2. 2 tRNA anticodons align with complimentary mRNA codons.

3. Strong peptide bond forms between 1st 2 amino acids, when 1st 2 anticodons are aligned.

4. 1st tRNA leaves ribosome.

5. Ribosome moves along mRNA so 3rd tRNA anticodon can align.

6. Peptide bond forms between 2nd and 3rd amino acids.

7. 2nd tRNA leaves ribsosome, and so on, until polypeptide chain is complete.http://www.biostudio.com/demo_freeman_protein_synthesis.htm

Stick in simplified translation diagram.

8. Peptide chain undergoes folding/rearrangement to become complete protein in the Golgi apparatus.

Protein made in free ribosome – used within the cell.

Protein made in ribosomes attached to RER – for export.

After protein synthesis – mRNA re-used, tRNA re-joins with amino acid.