Quick Review

1. What is genetic information stored as?

2. What organelle is this information found in?

First Model of DNA

• 1953: James Watson, Francis Crick and Maurice Wilkins examined an amazing photograph made by Rosalind Franklin using a technique she developed called X-ray crystallography 

• With what they had discovered about the composition of DNA and Franklin's photographs, Watson & Crick developed and proposed the first model for the structure of DNA

Watson and Crick Model

• consisted of two nucleotide chains that wrap around each other to form a double spiral.

• This shape is called a double helix.

DNA• DeoxyriboNucleic Acid

• Genetic code of life

• Located inside the nucleus

• NEVER leaves the nucleus

• Double Stranded

• Shape of DNA is a double helix

• Made of nucleotides

Primary functions of DNA:

1. Store and Transmit genetic information

2. Direct its synthesis/replication

3. Code for protein synthesis

So, what is RNA?

• RiboNucleic Acid

• Copy of a gene in DNA

• Responsible for delivering genetic information from the DNA in the cell nucleus to the ribosome in the cytoplasm

• Located outside the nucleus

• Responsible for completion of the process of protein synthesis

• Single stranded

• 3 Types of RNA: Messenger, Transfer, Ribosomal

• Made of nucleotides

DNA and RNA

Nucleotides

• Monomers that make up DNA & RNA

Each nucleotide is composed of:

• A sugar,

• A nitrogen base

• A phosphate group:

Sugar

• Deoxyribose - a 5-carbon sugar in DNA

• Ribose - a 5-carbon sugar in RNA. • This sugar has more oxygen than the sugar in DNA.

Notice: Oxygen placement

DEoxy (de means to remove. DNA has an Oxygen removed!!!

Nitrogen Base

Purines– have a double ring of

carbon and nitrogen atoms.

– Adenine & Guanine

Pyrimidines• have a single ring of carbon

and nitrogen atoms.• Thymine & Cytosine (in DNA)• Uracil & Cytosine ( in RNA)

Phosphate Group

• -PO4

The phosphate group is attached to the sugar, and the sugar is attached to the nitrogen base 

RNA – single stranded

DNA – double stranded

Two nucleotides pair to form one of the "rungs" of the ladder in a DNA

double helix. 

The sugar and phosphate groups form the "backbone" or outer support of the

DNA ladder-like double helix.

Sugar phosphate backbone

Base Pairing RulesBase Pairing RulesThese rules describe the behavior of the bases.

1. Cytosine always bonds with guanine by forming three hydrogen bonds. (C - G)

2. Adenine always bonds with thymine by forming two hydrogen bonds. (A - T) In the RNA nucleotide, thymine is replaced by Uracil (A – U).

3. A pair of bases that always bond together is known as a complementary base pair.

3 Basic Types of RNA

• Messenger RNA – mRNA

• Transfer RNA – tRNA

• Ribosomal RNA - rRNA

Messenger RNAmRNA

• carries genetic information from nucleus to cytoplasm

Transfer RNAtRNA

• carries amino acids from cytoplasm to ribosomes

Ribosomal RNArRNA

• consists of RNA nucleotides in globular form

Celebration of Learning Moment!

You are to create a comparison between RNA and DNA.

Be sure to include:

1. Type of Sugar

2. Type of nucleotides

3. Strand type

DNA & RNA Comparison

DNA RNA

Sugar molecule is Ribose

Sugar molecule is Deoxyribose

Is single stranded Is double stranded

Uses Uracil Uses Thymine

Is smaller and leaves the nucleus

Remains in the nucleus

Has 3 basic types Only one kind of DNA

COPY of genetic code Is THE genetic code