Chapter 13 –RNA and Protein Synthesis

Section 1 - RNA

RNA

• RNA stands for RiboNucleic Acid• RNA is a nucleic acid; therefore, made of

nucleotides• RNA works with DNA to make proteins• Proteins are made through a process called

protein synthesis• Review: Proteins are made of amino acids• Review: Proteins are made by ribosomes

Phosphate

5 – Carbon Sugar- Ribose (if RNA)- Deoxyribose (if DNA)

Nitrogen Base

• Guanine• Cytosine• Adenine• Thymine (only in DNA)• Uracil (only in RNA)

Differences between RNA and DNA

RNA• Has the sugar ribose• Single stranded• Has uracil

DNA• Has the sugar deoxyribose• Double stranded - double helix• Has thymine

The Nucleotides of RNA

DNA has the 5-carbon sugar, deoxyribose.

RNA has the 5-carbon sugar, ribose.

DNA has thymine, adenine, cytosine and guanine.

RNA has uracil, adenine, cytosine and guanine.

DNA is a double stranded molecule. It has base-pairs with hydrogen bonds between the nitrogen bases. The molecule is anti-parallel.

RNA is a single stranded molecule.

3 types of RNA

There are 3 major types of RNA:1. Messenger RNA (mRNA) – carries the genetic

code from DNA to the ribosome (site of protein synthesis)

2. Ribosomal RNA (rRNA) – makes the two subunits of ribosomes

3. Transfer RNA (tRNA) – transports amino acids (monomers of proteins) to the ribosomes

3 types of RNAMessenger RNA (mRNA) – carries code from DNA to ribosome for protein synthesis

Transfer RNA (tRNA) – transports specific amino acid to ribosome for protein synthesis

Ribosomal RNA (rRNA) – assembles amino acids brought by tRNA in a specific order from mRNA to make proteins; made of RNA by the nucleolus

Production of RNA

• RNA is made through a process called transcription– “trans” – across– “script” – to write

• DNA is split and one strand forms a template• A sequence of DNA that codes for a protein is

known as a gene• There are portions of DNA that do not code for

protein

Transcription

• DNA template is formed when it untwists and hydrogen bonds between nitrogen bases are broken

• RNA polymerase (an enzyme) binds complementary nucleotides to the template– Places Cytosine with Guanine– Places Adenine with Thymine– Places Guanine with Cytosine . . . BUT– Place URACIL with Adenine

• RNA DOES NOT HAVE THYMINE!!

Transcription

Transcription1. DNA “unzips”2. One side of DNA becomes a

template3. Free nucleotides of RNA attach to

open sites of the template by RNA Polymerase (not shown)• Cytosine attaches to Guanine• Uracil attaches to Adenine• Guanine attaches to Cytosine• Adenine attaches to Thymine

4. Messenger RNA is produced and released

5. mRNA is edited• Introns removed• Exons spliced together

6. mRNA goes to ribosomes for protein synthesis

Another look at transcription . . .

Transcription (cont’d)

• Transcription starts at a location called the promoter

• Promoter is a specific sequence of DNA that starts transcription

• Pre-RNA is produced• Introns are cut out and thrown out• Exons are spliced together to form mRNA• mRNA is sent to ribosomes to be decoded

Editing/Refining

• Introns and Exons are processed• Introns are removed and exons are

placed together• Exons are expressed; introns disappear• Purpose of introns are not known

A sequence of nitrogen bases on a segment of DNA of one of its strands that actually carries instructions for the order of amino acids in a protein is called a gene.

When DNA separates, one side becomes the template. Which side is the template? The side that is a code for a protein!

After transcription, a molecule of mRNA with codons is produced.

During translation, each codon of mRNA is matched with an anti-codon on a tRNA molecule with the amino acid it carries.