BIOLOGY DNA A DNA Structure Review DNA Deoxyribose
BIOLOGY DNA
A) DNA Structure Review • DNA- Deoxyribose Nucleic Acid • Discovered by Watson and Crick in 1953 – W/ the help of Rosalind Franklin • Stored in the Nucleus, to protect it • Monomer=Nucleotide – Sugar-Deoxyribose – Phosphate Group – Nitrogen Bases – Purines( A (adenine), G (guanine)-2 ringed Pyrimidines (C (cytosine), T(thymine))- 1 ring
• DNA is double stranded • Held together with hydrogen bonds • Hydrogen bonds link purine bases pyrimidine bases • Bases are complementary based paired, A=T, C ≡ G • 2 strands of DNA are anti-parallel, which means they run in opposite directions • DNA is spiraled, called a double helix • Genetic Information is stored in the sequence of N-bases, which translates to a sequence of amino acids that make up various proteins
B) DNA Replication • DNA Replication occurs during the synthesis phase( S-phase) of the interphase , which is part of the cell cycle • Used to make copies of the DNA so that each daughter cell produced though cell division (mitosis, meiosis, binary fission) has an exact copy of the parent DNA • Each new strand of DNA has one old strand of DNA and one new strand, so DNA replication is said to be semi-conservative
• If an error is made in copying the DNA code, this is called a mutation • The error rate of the enzymes involved in replication is 1/ per billion base pairs • a total of 3 errors occur on average every time the DNA is replicated Enzymes involved in DNA Replication DNA Helicase- unzips the DNA ‘s double helix DNA Polymerase- builds the new stand of the DNA, using the info from the template strand, has the ability to proof-read and correct the majority of errors DNA Ligase- used to link together the small fragments of new DNA created using the lagging template strand
Products of DNA Replication 2 identical strands of DNA are produced Each daughter strand has one old strand one new strand
Replication Step 1 – Initiation Unzip the double helix of DNA by breaking the Hydrogen Bonds between N-bases Lagging Template Strand Unzip this direction Replication Fork DNA Helicase Leading Template Strand
Replication Step 2 -Elongation DNA Polymerase attaches and makes a new copy of the DNA from the template strand, moving in both directions at one time The leading strand produces a continuous stand, because it moves toward the replication fork The lagging strand is produced in short pieces
Replication Step 3 -Termination DNA Ligase glues the short pieces of DNA from the lagging strand together and the strands separate producing two identical copies of DNA
DNA Replication Animation
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