Deoxyribonucleic acid DNA Deoxyribonucleic acid

DNA structure 1953 – James Watson and Francis Crick, at Cambridge University, England Double Helix – (twisted ladder) phosphate and sugar alternate on the sides Bases are held together by hydrogen bonds Complimentary bases: Adenine - thymine Cytosine – Guanine 1949 – Chargaff determined: % A = % T, % C = % G

White Board Practice What is the % of the other bases if A = 10%? T = 10 G = 20 80 2. What is the % of the other bases if C = 37%? C = 37 A = G = 37 T = 74 26

White Board Practice 3.What is the % of the other bases if T = 23%? T = 23 C = A = 23 G = 46 54 4.What is the % of the other bases if G= 3%? G = 3 A = C = 3 T = 6 94

Open the textbook to page 198 5. Which bases are purines and which bases are pyrimidines? Purines: A and G Pyrimidines: T and C 6. How does their structure differ? Purines have 2 rings and Pyrimidines have 1 ring 7. How does their structure and base pairing relate to overall DNA structure? Correct base pairing is 3 rings long, keeping the sides of the DNA molecule straight.

DNA Replication – DNA makes an exact copy of itself During which part of the cell cycle does replication occur? During S of interphase 2. Why must the copy be exact? to prevent mutations

3. What monomers make up the DNA molecule. nucleotides 4 3. What monomers make up the DNA molecule? nucleotides 4. What are the 3 parts of the DNA nucleotide? phosphate, deoxyribose sugar, base 5. Draw a DNA nucleotide.

DNA Replication Helicase (an enzyme) separates the DNA by breaking the hydrogen bonds (DNA unzips) DNA polymerase brings in nucleotides to bond with their complimentary bases DNA polymerase drops off, 2 DNA molecules are formed

Human chromosomes are very long. Replication occurs at 50 nucleotides per second. It would take 53 days to replicate 1 chromosome therefore: replication forks occur at many sites simultaneously to allow for rapid replication

RNA – ribonucleic acid contains Uracil, not thymine contains Ribose, not deoxyribose 3 types: Messenger RNA (mRNA) - brings messages from the nucleus into the cytoplasm - ribbon shape - contains codons

2. Ribosomal RNA (rRNA) - makes up the ribosome 3. Transfer RNA (tRNA) - brings amino acids to the ribosome - found in the cytoplasm - t-shaped - has anticodon

Transcription – making mRNA RNA polymerase (an enzyme) separates the DNA by breaking the hydrogen bonds (DNA unzips) RNA polymerase brings in RNA nucleotides to bond with their complimentary bases along one side of the DNA molecule RNA polymerase drops off, mRNA moves away, DNA molecule closes