DNA Structure and Replication PDF

DNA structure and replication **MLO3.   **Explain, with the aid of diagrams, how DNA is replicated, how cells divide, and distinguish between mitosis and meiosis. Ribose sugar vs deoxyribose A close-up of chemical structures Description automatically generated Deoxyribonucleic acid is named that...

DNA structure and replication **MLO3.   **Explain, with the aid of diagrams, how DNA is replicated, how cells divide, and distinguish between mitosis and meiosis. Ribose sugar vs deoxyribose A close-up of chemical structures Description automatically generated Deoxyribonucleic acid is named that way because all the nucleotides in it contain 2' deoxyribose. Nitrogenous bases include adenine (A), cytosine (C), guanine (G) and thymine (T). Adenine and guanine are purines because they have a double ring. Cytosine and thymine (and uracil) are pyrimidines because they only have a single ring. Nucleotides can have up to 3 phosphates attached together in a chain.  Nucleoside = base + sugar Nucleotide = nucleoside mono, di or tri -- phosphate Adenosine monophosphate (AMP) = Adenine, ribose, one phosphate Uridine monophosphate (UMP) = Uracil, ribose, one phosphate Guanosine monophosphate (GMP) = Guanine, ribose, one phosphate Cytidine monophosphate (CMP) = Cytosine, ribose, one phosphate DNA can be identified because the nucleotides lack a 2'OH group Features of DNA: - Nucleotide chain is linked by phosphodiester bonds - DNA is polar; 3' end of DNA at the bottom has a free OH/5' end of DNA at the top has a free phosphate - DNA has a sequence, which is the order in which the different bases appear in the chain. - Strands of DNA are antiparallel - Inside of double helix is highly hydrophobic DNA forms a double helix because the two strands are held together by hydrogen bonds between adjacent bases that are complimentary (Watson-Crick base pairs) The 5'-3' strand of DNA codes for protein X wherease the produced mRNA 3'-5' is the mold for making the coding strand. DNA polymerases synthesize DNA using a template DNA stand creating a double stranded structure as a product. The sequence on the 5'-3' is called a primer, which is required for DNA polymerase to start. DNA polymerase requires deoxynucloside triphosphates to synthesize DNA, and will only work if the free nucleotides are complimentary to the original strand. DNA polymerase only adds the new nucleotide at the 3' end of the growing strand -- this is known as 5'-3' synthesis. DNA replication process: - Initiation factors bind to origins of replication, separating DNA strands (melting) - Helicase binds to melted sites, unwinding DNA forcing the strands apart, creatinf a replication bubble - Replication bubble is kept open by a single stranded DNA binding protein - The edges of the bubble where helicase is unwinding are called replication forks - DNA primase synthesizes RNA primer, which extends in 3' end direction - Top strand (leading strand) synthesizes DNA as helicase moves along creating one long DNA strand - Another primer is synthesized so DNA is synthesized in the direction that leads away from the replication fork. This means the lagging strand is made in short fragments (Okazaki fragments)