DNA REPLICATION

Genes- sequence of DNA that codes for a protein Important Vocabulary Genes- sequence of DNA that codes for a protein Chromosome- long strand of tightly bound DNA DNA- contains the genetic code which determines the characteristics of a living thing DNA Replication-The process of producing a copy of a DNA molecule

Need an EXACT copy of DNA so the new cell can carry out its function DNA separates into 2 strands Each strand is now a template for a new strand REPLICATION OCCURS DURING THE S PHASE OF INTERPHASE Cell can then go through mitosis or meiosis

A Closer Look… Each of your cells has 46 DNA molecules in its nucleus (one long double helical molecule per chromosome) We have 6 billion base pairs that can be copied in a couple of hours E. Coli 4.6 million base pairs that can replicate in an hour;

Where Replication Begins: Begins at sites called the origins of replication (there are many) Enzymes initiate DNA replication The two strands separate at the replication fork, and create a replication bubble DNA replication proceeds in both directions until copying is finished!

DNA Replication happens through the help of ENZYMES

HELICASE- unzips the molecule of DNA by breaking the hydrogen bonds between the base pairs and creates TWO templates

PRIMASE- provides a starting point for DNA synthesis Origin of Replication

DNA POLYMERASE- adds nucleotides to the DNA strands “the builder” Can only synthesis in the 5’ to 3’ direction!!!

2nd Step in Replication Polymerase- joins individual nucleotides producing a new DNA strand; it also proofreads each new strand DNA strands are antiparallel (oriented in opposite directions) 50 nucleotides are copied per second

Remember DNA strands are anti-parallel (opposite directions) One side is 3’ to 5’ (leading strand) One side is 5’ to 3’ (lagging strand)

Leading strand 3’ to 5’ (Can be synthesized continuously) Lagging strand 5’ to 3’ (synthesized in short fragments)

2nd Step in Replication (Continued) DNA strand elongates in a 5’-3’ direction (5’ leads w/ phosphate & 3’ leads w/ sugar) The strand being built 5’-3’, has Polymerase continuously adding base pairs→ leading strand (built on the 3’-5’ strand) The strand that is built 3’-5’, has Polymerase synthesizing in segments → lagging strand (Okazaki fragments) (built on the 5’-3’ strand)

Okazaki Fragments- short fragments of DNA produced on lagging strand

DNA LIGASE- joins or “glues” those short okazaki fragments together

3. Telomerase- adds short repeated DNA sequences to the telomeres Telomeres- DNA at the chromosome tips; difficult to replicate (especially lagging strands) Helps prevent genes from being lost or damaged in replication DNA replication is unable to reach the ends of the telomeres, and thus ends at the telomere region. This shortens the telomere region of the daughter strand. Cells can only divide a certain number of times before the DNA loss prevents further division. Telomerase plays a role in adding short repeating sequences of DNA. If telomerase is overly activated, could cause cancer. http://www.youtube.com/watch?v=hfZ8o9D1tus&feature=related http://www.youtube.com/watch?v=oNW_ykH3AvA&feature=related

Wow that was a lot of information How about some bingo???

The enzyme that provides a starting point for DNA synthesis

A sequence of DNA that codes for proteins

Opposite directions

This strand is synthesized continuously

This enzyme synthesizes DNA by adding nucleotides to template strands

Tightly coiled DNA

This enzyme unwinds the two strands of DNA

DNA replication occurs during this phase of interphase

Short fragments of DNA produced on lagging strand

The region where DNA replication begins

contains the genetic code which determines the characteristics of a living thing

This enzyme glues together the okazaki fragments

The process by which DNA is duplicated

The open area where DNA synthesis occurs

What is a mutation? Mutations Mistake in copying DNA Heritable changes in genetic info Like playing telephone- you whisper a message and it spreads around the circle; if one person mishears the message, it gets passed on inaccurately to the next message. The final message can be quite different than the original message.

Harmful or Beneficial? Harmful – change protein structure or gene activity dramatically Can disrupt normal biological activities → genetic disorders (ie. Genetic disorders) Beneficial- proteins are altered in a way that causes positive/useful effects to organisms Can be useful to organisms in different or changing environments Silent- an alteration in a DNA sequence that does not result in a change in protein Bad mutations- can cause cancer, sickle cell anemia, color blindness, Muscular Dystrophy, Haemophilia, Tay Sach’s Disease Good mutations- genetic variety in species, mutations that increase resistance to HIV, mutation that decreases the risk of Type II Diabetes, antibiotic resistance in bacteria & insects;

Problems with Replication- Mutations Frame Shift Mutations Deletion Frameshift Mutation- A base is accidentally left out Insertion Frameshift Mutation- A base is accidentally inserted Point Mutation/Substitution- The wrong base is substituted Environmental agents or radiation may also change the base sequence- mutagens X- rays, ultraviolet light, chemical mutations, radiation, tobacco smoke, etc.

Deletion Frameshift DNA strand: ACG TAG GTC TCG AAT Replicated strand: TGC ACC AGA GCT TA

Insertion Frameshift DNA strand: ACG TAG GTC TCG AAT Replicated strand: TGC AAT CCA GAG CTT A

Point Mutation DNA strand: ACG TAG GTC TCG AAT Replicated strand: TCC ATC CAG AGC TTA

Identify the following mutation: Original strand: TCG GTA ATC GAT Replicated strand: AGC ATT AGC TA Original strand: TCG TAG AAG TAC Replicated strand: AA C ATC TTC TTG