Notes on Nucleic Acids 2 types of nucleic acids: DNA – deoxyribonucleic acid RNA – ribonucleic acid Chapter 8.

Notes on Nucleic Acids

2 types of nucleic acids:

DNA – deoxyribonucleic acid

RNA – ribonucleic acid

Chapter 8

• organic compounds

• large, made of subunits called nucleotides

Click image for interactive journey into human DNA

Each DNA nucleotide is made up of 3 parts:

1. Phosphate group

2. Deoxyribose – 5 carbon sugar

3. Nitrogen base – either adenine, thymine, cytosine, or guanine

Nitrogen bases

Purines – adenine (A) and guanine (G)

Pyrimidines – thymine (T) and cytosine (C)

The bases are held together by weak hydrogen bonds

Base pairings in DNA: A – T

C – G

A model of DNA was constructed in 1953 at Cambridge University in England

Scientist – James Watson, (1951-1953)

Field of study – biology

Country - America

Scientist – Francis Crick (1951-1953)

Field of study – biophysics

Country - England

Their model is described as a double twisted helix

(looks like a twisted ladder)

Watson and Crick published their proposed DNA double helical structure in a paper in the journal Nature in April 1953. In this paper Watson and Crick acknowledged that they had been "stimulated by.... the unpublished results and ideas" of Wilkins and Franklin.

Scientist – Maurice Wilkins, (1950-1953)

Field of study – biophysics

Country - England

Scientist – Rosalind Franklin, (1951-1953)

Field of study – Molecular Biology

(x-ray diffraction)

Country - England

Click image for interpret-ation of the X-ray

The process by which DNA builds an exact copy of itself - replication

• first the double helix must be unwound – this is done by enzymes called helicases

• then DNA polymerases (enzymes which move along each DNA strand) add nucleotides to the exposed bases

Replication occurs every time a cell divides, therefore passing the DNA code on into every cell

Genes are the DNA-encoded information that specifies particular proteins;

Each gene is made of a specific sequence of nucleotides

The working structures of genes are made of RNA

RNA structure:

1. Consists of a single strand of nucleotides

2. Ribose – a 5 carbon sugar

3. Uracil (U) instead of thymine (T)

uracil is paired with adenine

RNA base pairings: A – U

C – G

Three types of RNA

1. mRNA – messenger RNA

2. tRNA – transfer RNA

3. rRNA – ribosomal RNA

• All are needed for processing the information from DNA into proteins (gene expression)

Differences in DNA and RNA:

DNA RNA

1. double stranded single stranded

2. thymine uracil

3. nucleus only cytoplasm

4. deoxyribose sugar ribose sugar

Gene expression occurs in two stages:

1. Transcription – information in DNA is transferred to mRNA

2. Translation – the information in mRNA is used to make a protein

Roles of DNA & RNA in transmitting genetic information

• Story time: the analogy…

• Comp Book– Draw the Flow Map: DNA expression in the cell

• You need your pencil plus three colors:– Pencil will draw cell membrane/ cell parts/ labels– RED: DNA molecules– BLUE: any RNA molecules– PURPLE: protein

DNA RNA

RNA protein

1. Transcription (DNA RNA)

• occurs in nucleus

• begins with the enzyme RNA polymerase which binds to the promoter

Promoter – a specific sequence of DNA that acts as a “start” signal for transcription

Terminator – a sequence of bases that tells the RNA polymerase to stop adding nucleotides

Transcription Video

mRNA – is an RNA copy of a gene used as a blueprint for a protein

• carries hereditary information from DNA and delivers it to the site of translation

• acts as a template for the assembly of amino acids

tRNA – acts as an interpreter molecule

• translating mRNA sequences into amino acid sequences

rRNA – plays a structural role in ribosomes

2. Translation (RNA proteins)

• occurs in cytoplasm @ a ribosome

—both free ribosomes & ribosomes attached to ER

• uses nucleic acids to synthesize proteins

• involves all three RNA types:

—rRNA in the ribosome

—mRNA containing the genetic message

—message is made of codons

AUG-AAA-UAC-CCU-CCA-GCG-GGA

Codon – a series of three-nucleotide sequences

• each codon corresponds to an amino acid or signifies a start or stop signal

Write this down!

—tRNA carrying specific amino acids to be joined

a.a.

AUG-AAA-UAC-CCU-CCA-GCG-GGAmRNA

tRNA

UAC

tRNA

tRNA

tRNA

GGAAUG

GGU

ProtRNA

UUU

ribosome

Met

Lys TyrSer

Translation (Example)

Growing polypeptide

Translation: mRNA, tRNA & rRNA in cooperative action

…to make proteins!!!

AUG-AAA-UAC-CCU-CCA-GCG-GGAmRNA

tRNA

UAC

tRNA

tRNA

tRNA

GGAAUG

GGU

ProtRNA

UUU

ribosome

Met

Lys TyrSer

Translation (Repeated)

Growing polypeptide

Translation Video

A “Polysome”

Can you ID the 3 RNAs?

Awesome summary video from www.youtube.com

Click here to view