• 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: Phosphate Base
Deoxyribose sugar
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 sugarphosphate backbone.
Strong chemical bond.
4 different bases: Adenine (A), Thymine (T), Cytosine (C), and Guanine (G).
T
C
A
G
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.
T
C
A
G
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 CTCTGTAAATGC 2. C T T G C C A A T A C G GAACGGTTATGC 3. A G C T T G A C C A T G TCGAACTGGTAC
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 CUCUGUAAAUGC 2. C T T G C C A A T A C G GAACGGUUAUGC 3. A G C T T G A C C A T G UCGAACUGGUAC
• 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
Fig. 9.4 p.70 1.DNA helix unwinds. 2. Weak H bonds between bases break => 2 DNA strands separate with bases exposed.
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 2 nd 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.