DNA The BIG show! All animations are from Virtual CellAnimation Collection .

DNA

The BIG show!

All animations are from Virtual CellAnimation Collection

http://vcell.ndsu.edu/animations/home.htm

Watson and Crick

1953 the structure of DNA was finally described

Based on Roselind Franklin and Maurice Wilkins’ crystallography of DNA (Wilkins shared in Nobel prize 1962 – Franklin had died)

http://www.odec.ca/projects/2007/knig7d2/images/WatsonCrick.jpg

Double Stranded Helix

DNA is comprised of two strands of nucleic

acids - bases 6 carbon sugar –

phosphate backbone helix – twists around

each other, like the stripes of a peppermint stick

http://whyfiles.org/034clone/images/dna_molecule.gif

Structure of DNA

Primary Sequence of base pairs

along one strand – ATGC Secondary

DNA is wrapped around histones

Tertiary Histones are grouped into

bundles Quaternary

DNA located on pairs of Chromosomes

http://employees.csbsju.edu/hjakubowski/classes/ch331/DNA/chromosome.gif

Nucleotides

DNA is made up of subunits which scientists called nucleotides. Each nucleotide is made up of a sugar, a phosphate and a base. There are 4 different bases in a DNA molecule:

adenine (a purine) cytosine (a pyrimidine) guanine (a purine) thymine (a pyrimidine)

The number of purine bases equals the number of pyrimidine bases

The number of adenine bases equals the number of thymine bases

The number of guanine bases equals the number of cytosine bases

The basic structure of the DNA molecule is helical, with the bases being stacked on top of each other

What does that mean?

Adenine is hydrogen bonded to Thymine

Guanine is hydrogen bonded to Cytosine

DNA is directional from 5’ to 3’

http://porpax.bio.miami.edu/~cmallery/150/gene/c16x6base-pairs.jpg

Directional?

The DNA is “read” from the 5’ to the 3’ end, just like we read words from left to right

When DNA is replicated, it is read from 5’ to 3’

The two strands unzip to allow room for replication factors

https://eapbiofield.wikispaces.com/file/view/DNA-replication.jpg

Why is that important

Double stranded adds stability to DNA

Easy to find errors in copying or transcribing to RNA or mutations Easy to find T with a G or

C with an A

http://www.science.mcmaster.ca/mciars/Doug%20Boreham/Website_July2/Images_forwebsite/prymidine_dimer.jpg

Genes

Areas of DNA have readable sequences which code for genes

Many parts of the genome are “junk DNA” Genes can have differences in the AT and

GC, which form alleles If not detrimental, the mutation will continue If advantageous, the allele will become more

common

Questions?

BJ Shaw Panochthus frenzelianus American Museum of Natural History 2004

DNA to RNA to Protein

Overview

How it works DNA – double stranded

to protect and reduce the mutations

RNA – unstable, and breaks down quickly in the cell

Types of RNA

mRNA (messenger RNA) is transcribed from DNA

tRNA (transfer RNA) is the molecule that carries amino acids

rRNA (ribosomal RNA) reads mRNA and matches tRNA to build the protein in the correct sequence

http://www.aps.anl.gov/Science/Highlights/2001/Images/ribomain.gif

Types of RNA

cRNA (catalytic RNA) catalyses many reactions in the cytoplasm of the cell.

snRNA (small nuclear RNA) have various roles in the processing of the other classes of RNA.

snoRNA (small nucleolar RNA) over 100 of them found in the nucleolus where they are involved in several functions including making ribosomes

Amino Acids

Four nucleotides (Adenine, Thymine, Guanine, and Cytosine) translate into 20 different amino acids If 1 nucleotide = 1 amino

acid, only 4 amino acids If 2 nucleotides = 1

amino acid, then 16 amino acids (still short)

If 3 nucleotides = 1 amino acid, then 64 amino acids (too many)

http://www.ccs.k12.in.us/chsTeachers/BYost/Biology%20Notes/translation_files/image007.jpg

Amino Acids

Closer look… AUG = methionine, the

start of the protein sequence

UAA = stop UAG = stop UGA = stop Other codes allow for

“wobble” room For example, serine

starts with a UC, and any other nucleotide

http://www.ccs.k12.in.us/chsTeachers/BYost/Biology%20Notes/translation_files/image007.jpg

Protein Synthesis

DNA unzips Similar to replication,

DNA is copied (transcription)

Uracil is the molecule that pairs with Adenine rather than Thiamine

http://upload.wikimedia.org/wikipedia/commons/5/5e/RNA_polymerase_%281i6h%29.png

Protein Synthesis

mRNA is edited mRNA is spliced mRNA exits the

nucleus of the cell and is associate with the small subunit of rRNA (a ribosome) for translation

The protein is constructed one amino acid at a time

Proteins

Complex molecules One of the four major types

of molecules found within the cell DNA, RNA, and lipids are

the other three These comprise the

variation found within populations The amount of melanin will

determine the color of the iris – or it is at least 74% responsible

http://discovermagazine.com/2007/mar/eye-color-explained/eyes-400.jpg

Questions?

BJ Shaw Megatherium americanum Museo de La Plata 2008