Study guide for Ch 16-18
• Alfred Hershey and Martha chase answered the question whether protein or DNA was the genetic material by using Bacteriophages (viruses that infect bacteria). o Bacteriaphages were good for the experiment because they only contain 2 organic compounds, DNA and protein. • James Watson and Francis Crick were the first to solve the structure (structure=function) of DNA. • X-ray crystallography( process used to visualize molecules in 3-D. • DNA is a double helix- structure
• The nitrogenous bases of DNA are( adenine (A), thymine (T), guanine (G), and cytosine (C). • The 2 strands (the leading and the lagging strand) are antiparallel. o The leading strand goes in direction 5’ to 3’. o Lagging strand goes 3’ to 5’. Takes longer to replicate cause it’s built in fragments. • Tip from the book(know these enzymes for replication: DNA polymerase, ligase, helicase, and topoisomerase. Know this enzyme for transcription(the role of RNA polymerase. • Replication(making DNA from already existing DNA strand. DNA replication is semiconservative (1/2 of original DNA and the other ½ is from new DNA strand). This is used by humans! o A group of enzymes called DNA polymerases catalyzes the elongation of new DNA at replication fork. The overall direction of DNA replication goes from the origin to the fork. o DNA polymerase adds nucleotides to the growing chain one by one; working in a 5’ to 3’ (DNA build strand (“new”) or RNA polymerase go 5’(3’ in the build strand). Parent strand DNA and RNA polymerase is 3’ to 5’. o DNA polymerase matches adenine with thymine and guanine with cytosine o The lagging strand is synthesized in separate pieces called Okazaki fragments (which segments in 3’(5’), which are then sealed together by DNA Ligase. Forming a continuous DNA strand. • Many factors in replication:
o Base pairing in DNA replication( A=T/ G=C.
o Mismatch repair(special repair enzymes fix incorrectly paired nucleotides o Nucleotide excision repair.
• Tip****(know the difference between replication (DNA to DNA), transcription (DNA to RNA), and translation (RNA to protein). • In Eukaryotic cells, DNA and protein are packed together as chromatin. o Heterochromatin(very condensed chromatin.
o Euchromatin(loosely condensed chromatin.
• Telemer region(small fragment of DNA that is lost during replication due to enzyme’s inability to attach the fragment on to the end of the DNA helix. (This is our biological clock).
• Gene expression(the process by which DNA directs the synthesis of proteins (or sometimes RNA). • Transcription= DNA(RNA
o Takes place in the nucleus in eukaryotic cells.
• Messenger RNA (mRNA) produced during transcription. It carries the genetic message of DNA to the protein making machinery of the cell in the cytoplasm, ie the ribosome. • The mRNA triplets are called codons (a codon is a mRNA triplet). o mRNA is read codon by codon.
▪ Start codons and stop codons are used in the build strand the protein coding segment is between the start codon and stop codon in the build strand. • They are written in the 5’ to 3’ direction.
• More than one codon codes for each of the 20 amino acids. Genetic code includes 64 codons (4 x 4 x 4). o The group must be read in the correct groupings in order for translation to be successful o 3 codons act as signal terminators (UAA, UAG, UGA) o AUG always has to be start codon.
• RNA polymerase(enzyme that separates the 2 DNA strands and connects the RNA nucleotides as they base-pair along the DNA template strand. o RNA pol. Can add RNA nucleotides only to the 3’ end of the strand. REMEMBER… uracil replaces thymine when base pairing to adenine.==>difference betw DNA and RNA....
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