Put the following stages of the cell cycle (interphase, prophase, metaphase, anaphase, telophase/cytokinesis) in order. (6 points) d c e a b D, A, C, B, E

What is DNA? DNA is short for Deoxyribose Nucleic Acid. It holds an organism’s genetic instruction manual (code), and it is made up of nucleotides.

Remember nucleotides? Five-carbon sugar (deoxyribOSE) Phosphate group Nitrogenous base (A, T, C, G)

Why is DNA so important? DNA is like an instruction manual or a blueprint. It contains all of the instructions for how to make proteins that in return make up an organism.

Why is DNA so important? Specific parts of DNA called genes code for specific proteins that determine our appearance and other physical traits. EVERY CELL needs to have DNA in it. Without DNA, different types of cells wouldn’t be able to make proteins; living organisms could not survive without DNA.

What does DNA look like?

What does DNA look like? DNA is double-stranded and has a double-helix shape, sort of like a twisted ladder – the sugars and phosphates are like the sides of the ladder and the nitrogenous bases are like the rungs (what you stand on).

Bases are bonded to the deoxyribose sugar and hydrogen bonded to its compliment base DNA is double-stranded, with each strand going in opposite directions (5’ to 3’) – then twisted into a helix The alternating phosphates and sugars make up the DNA backbone

What does DNA look like? Each base bonds to another base across from it by weak hydrogen bonds, and each pairs up in a specific way:

evolution.berkeley.edu/.../dna_structure.gif

What does DNA look like? DNA has four possible nitrogenous bases: Adenine (A) Cytosine (C) Guanine (G) Thymine (T)

[A=T] Adenine (A) --- Thymine (T) [C=G] Cytosine (C) --- Guanine (G) Base Pairing Rules [A=T] Adenine (A) --- Thymine (T) [C=G] Cytosine (C) --- Guanine (G)

The sequence of these bases is like a code, or a computer language, that carries information.

Base Pairing Rules If you know the order of bases on one strand, you can predict the sequence on the other: Example: A C T A C C G G T A C C A T A ____________________________

How did we discover DNA? In the early 1950s, Rosalind Franklin took X-ray crystallography photos of DNA She was the first to figure out that DNA was a double-helix, but she didn’t want to share her results until she was absolutely certain.

https://www.evernote.com/shard/s2/sh/1c8a7050-8ce4-451f-8ca4-412566d10958/9bc615dc36ad0000e2598b97e4990494/res/751577b9-d090-4c9f-b06c-677b51c4c768/16_06_XrayDiffraction-L.jpg?resizeSmall&width=832

How did we discover DNA? In 1953, James Watson and Francis Crick proposed the double helix model of DNA. In 1962, they won the Nobel Prize for medicine for their work.

www.emc.maricopa.edu

How did we discover DNA? Watson, Crick and Maurice Wilkins (a member of Franklin’s research team) all won the Nobel Prize. However, the Nobel Prize can only be shared among three winners and it only goes to living recipients (Franklin died of ovarian cancer in 1958).

Warm-Up 3/8/13 Yesterday, we talked about DNA…. 1. A pairs with _____ G pairs with _____ Name at least two people who contributed to discovering the structure of DNA.

Think back to INTERPHASE… Interphase has three parts: G1, S, and G2

Think back to INTERPHASE… Before a cell can divide by mitosis or meiosis, it must make a copy of its DNA --- this is called SYNTHESIS. Without replication, new cells would only have half of the DNA of their parents.

Think back to INTERPHASE… Before a cell can divide by mitosis or meiosis, it must make a copy of its DNA --- this is called SYNTHESIS. Without replication, new cells would only have half of the DNA of their parents.

Think back to INTERPHASE… In the S phase, the DNA is copied so that there will be a full set of chromosomes for each of the daughter cells. The ‘S’ stands for ‘synthesis’ - synthesis means ‘making something’. In this phase, we are making DNA. This process is called DNA replication.

DNA REPLICATION What? Copying DNA in order to make 2 identical copies Where? Takes place in the nucleus Why? So cells can have two identical copies of DNA after mitosis and cell division How?

Steps in DNA Replication: Separation of Strands DNA helicase ‘unzips’ DNA Hydrogen bonds that hold base pairs together are broken (these are weak bonds).

Steps in DNA Replication: Base Pairing Free nucleotides pair with exposed nucleotides on both sides of the unzipped DNA.

Steps in DNA Replication: Bonding of Bases DNA polymerase bonds new nucleotides to the template strands

Steps in DNA Replication: Bonding of Bases Sugars and phosphates of the “new” nucleotides are bonded to form a strong “backbone”

Steps in DNA Replication: Results of Replication This process results in 2 identical DNA strands. 1 strand 2 strands

Steps in DNA Replication: Results of Replication ½ of each is from the template strand and ½ has been newly synthesized (made) This is called semiconservative replication. 1 strand 2 strands

Now the cell has two sets of chromosomes so that when it divides, both new cells have their own set of chromosomes.

DNA Coloring: Deoxyribose: purple Phosphate: brown Adenine: red Cytosine: yellow Guanine: green Thymine: blue