From DNA to Polypeptide

Fun Times with the Double Helix

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Itself is not alive…

Exists for only one reason… to make more DNA

2 meters squeezed into each cell ~2o million km!

Holds the instructions to make and maintain you.

Contains roughly 3.2 billion letters- 103,480,000,000

combinations

Is 99.9% identical to everyone else’s DNA

Is 0.1% completely and utterly unique to you.

James Watson and Francis Crick- discovered the structure of DNA– the double helix

http://www.youtube.com/watch?v=sf0YXnAFBs8

4 types of nucleotides, A,T, C, G

Complementary base pairing:

A = T

C = G

DNA inside nucleus makes copy of itself during _____ stage of _______________.

Part of the DNA helix unwinds (by enzyme “helicase”) when H+ bonds between nitrogenous bases are broken.

Each strand serves as a pattern for a new strand of DNA

Enzyme DNA Polymerase moves along each separate strand and matches bases (A, C, T, G) on each strand to a new base that is “floating” inside the nucleus.

H+ bonds reform between bases…

Each strand of DNA serves as a template for a new strand.

The replicated DNA is made of one old strand and one new strand

http://www.youtube.com/watch?v=4jtmOZaIvS0&feature=related

http://www.youtube.com/watch?v=d1UPf7lXeO8&feature=related

How does a cell interpret DNA?

Simulation:

Group A: Design a structure using all the materials in the ziplock bag.

Devise a way to communicate with Group B how to duplicate this design… no words, no pictures… all blueprints stay at Group A site.

From DNA to messenger RNA

Making a protein (polypeptide) begins with making mRNA (messengerRNA) inside the nucleus.

RNA is also a “nucleic acid”

is single-stranded

has “uracil” (U) instead of thymine

has 5C sugar “ribose”

Step 1: DNA strand separates at a gene spot on DNA.

Only 1 strand of DNA will serve as a template- starts at a “promoter”

Step 2: Enzyme “RNA polymerase” matches RNA bases with DNA bases: A, U, C, G

Step 3: Enzymes link RNA nucleotides together into a single-strand of RNA.

Step 4: mRNA leaves nucleus with code for protein and moves to ribosomes where the protein will be made.

Important editing is required of mRNA:

Introns: cut-out connected sequences

Exons: expressed sequences spliced together- final edited RNA

http://www.youtube.com/watch?v=5MfSYnItYvg&feature=relmfu

There are actually many types of RNA.

In most cells three kinds of RNA are critical to the making of proteins.

mRNA – “messenger RNA” carry copies of the instructions for the proteins from the DNA to the ribosomes

rRNA – “ribosomal RNA” are part of the ribosomal structure

tRNA - “transfer RNA” transfers the amino acids to the ribosomes to make the protein

Making of proteins is called “protein synthesis”

Instructions for each protein comes from the mRNA in 3-base messages called “codons”

Codons are translated in the ribosomes. mRNA attaches to the ribosome (rRNA)

“Translation” is the decoding of the message from the mRNA into a polypeptide chain (protein).

The tRNA is a cloverleaf-shaped molecule that has on one end a complementary “anticodon” and on the other end an amino acid.

Example: codon AAA, anticodon UUU or lysine

As the codons from the mRNA are “read” inside the ribosome and the tRNA delivers one amino acid at a time…

these amino acids bond together with “polypeptide” bonds …

the “language” of mRNA instructions is called the Genetic Code…

How can 3 base codons make 20 amino acids?

(4 x 4 x 4) = 64 possibilities

http://www.youtube.com/watch?v=41_Ne5mS2ls&NR=1