Presentation on theme: "Molecular Basis of Inheritance Chapter 16. DNA as Genetic Material Watson and Crick – 1 st scientists to propose structure of DNA - responsible for transmission."— Presentation transcript:
To replicate - virus infects host cell; takes over cell’s metabolic machinery. Viruses that specifically attack bacteria - bacteriophages (phages) Hershey and Chase labeled protein and DNA - injected them into bacteria.
Hershey and Chase concluded that injected DNA of phage provides genetic information that makes infected cells produce new viral DNA and proteins, which assemble into new viruses. DNA doubles prior to mitosis.
DNA Replication and Repair Watson and Crick discovered each strand of DNA can make template to make more DNA. Cell copies DNA - each strand forms as template to determine new complementary bases. Nucleotides pair in complementary fashion, one by one.
Origins of replication - where replication process begins. Bacteria - 1 site - replication looks like bubble moving along DNA. Eukaryotes - many origins of replication on each chromosome. Origin sites - DNA strands separate forming replication “bubble” with replication forks at each end.
1 parent strand (leading strand - one that runs 3’ to 5’) used as template to keep complementary strand continuous. Other strand (lagging strand - one that runs 5’ to 3’) copied from fork in small segments - Okazaki fragments.
Once primer formed, polymerase can add DNA nucleotides to growing daughter strand of DNA. Later - different DNA polymerase replaces original RNA with new complementary DNA nucleotides - there is no RNA left in strand.
X-rays and UV rays can alter DNA after replication. Mistakes can be fixed after DNA synthesis because cell continually monitors DNA. Mismatch repair, special enzymes fix incorrectly paired nucleotides - happens in certain types of cancers.
Xeroderma pigmentosa (genetic disease) cannot go through process. Disease prevents person from going in sun because UV rays interfere with DNA replication. More susceptible to skin cancer because they cannot fix mistakes.
Telomerase not present in all cells - life span to certain tissues or organism itself. Important for telomerase to be present in gamete cells so they can pass long telomeres on to zygote. Active telomerase in body cells can be responsible for cancer cells because cells keep dividing.