RNA & Protein Synthesis

I. DNA to Genes• A. We now know how the double

helix is replicated but we still don’t know how it is then transformed into genes.

• B. Remember genes are coded DNA instructions that control the production of proteins within the cell.

• C. A little sequence from DNA is copied and transferred into RNA, which then carry the sequence to make proteins

II. What is RNA: Structure of RNA• A. RNA consists of a long single stranded

chain of nucleotides. • B. The 3 parts of a RNA nucleotide:– 1. 5 carbon sugar ribose– 2. Phosphate group– 3. Nitrogenous bases : Adenine, Guanine,

Cytosine & Uracil

• C. RNA can be a disposable copy of a tiny segment of DNA that carries a sequence for a single gene

III. Types of RNA• A. There are 3 main types of RNA:– 1. messenger RNA – carry the copy of DNA to the rest of the

cell during transciption (mRNA)– 2. ribosomal RNA – along with proteins make up ribosomes

that is composed of 2 subunits (rRNA). The large subunit has 3 binding sites (A, P &E) for tRNA while the small subunit has one binding site for mRNA. This structure is used during translation

– 3. transfer RNA – carry an amino acid to the ribosome to bind with mRNA (tRNA)

• B. The 3 types of RNA play a key role in protein synthesis

IV. Transcription• A. Transcription is the process in which RNA molecules are

produced by copying a specific part of the DNA nucleotide sequence.– 1. It has 3 stages: initiation, elongation & termination

• B. During transcription RNA polymerase binds to DNA and separates the DNA at a promoter site using one DNA strand as a template.– 1. promoter – a section of DNA with a specific base

sequence (TATA box )that indicates to RNA polymerase to bind and begin transcription

– 2. Transcription initiation complex

IV. Transcription• C. During elongation RNA polymerase continues to

pry DNA apart and add RNA nucleotides to the 3’ end building 5’ to 3’. (A-U and C-G)

• D. Termination is when mRNA cuts free from DNA template at the sequence AAUAAA.

V. RNA Editing• A. The new RNA molecule requires a little bit of

editing getting copied directly from DNA.• B. DNA in eukaryotic cells have sections of

nucleotides called introns that are not involved in coding for proteins and are removed by snRNPs (small nuclear ribonucleoproteins) & spicesomes.

• C. The sequences that code for proteins on DNA are known as exons. (expressing sections)

• D. Prior to leaving the nucleus the introns are cut out and the exons are spliced back together

Regulation ProteinsSpecific per cell

V. RNA Editing• E. The 5’ cap modified guanine nucleotide is added

to the 5’end. This cap helps the RNA bind to the ribosome during translation.

• F. The 3’ end has a poly A tail consisting of adenine bases to protect the strand and allows easy release from the nucleus.

VI. Genetic Code• A. Proteins are made by joining the 20 different

amino acids into long chains called polypeptides– 1. the sequence of the amino acids determines the

protein• B. The genetic code from the DNA transcribed into

mRNA is read 3 letters at a time making each amino acid a different 3 letter “word”

• C. The 3 letter transcription unit along the mRNA is called the codon the tRNA that carries the amino acid to match the codon is called the anticodon.

• 1. There are over 64 possibilities of codons but only 20 amino acids so many codons may read for the same amino acid. (redundancies but no ambiguity)

• 2. There is also a very specific codon (AUG) that is known as a start codon that starts protein synthesis while UAA, UGA and UGA are stop codons and terminate the sequence

• 3. Some tRNA molecules have anticodons that can recognize 2 or more codons. Rules for the 3rd base are not strict, this is called the wobble. – Ex. DNA Sequence: AGC GTGmRNA Sequence codon: UCG CACAmino Acid that will match: Serine Histidine

VII. Translation• A. In order for proteins to be made from the mRNA the

ribosome has to carry out its main job – 1. Decoding the mRNA message into a polypeptide chain (amino

acid sequence) is known as translation• B. As the mRNA is moves through the ribosome tRNA brings

the correct amino acid to the ribosome with the help of aminoacyle-tRNA synthetase to match with the codon, as the ribosome assembles the amino acids into a chain it releases the tRNA to be used again. (GTP guanosine triphosphate gives this process its energy)

• Once the ribosome reaches a stop codon the polypeptide chain as well as the mRNA are released as well

IIX. Mutations• A. Mutations are changes in the genetic material.– 1. Can be caused by mutagenic agents (toxic chemicals &

radiation)• a. somatic vs. gamete mutations

• B. 2 types of mutations:– 1. Gene mutations – changes in a few nucleotides can cause

either point mutations or frameshift mutations (insertion or deletion)

Ex. TAC GCA -> AUG CGU -> Met Arg TAC GTA -> AUG CAU -> Met HisEx. Sickle cell anemia (point mutation)Missense or nonsense mutation

IX. Comparing Roles of DNA & RNA

A. DNA• 1. Double stranded• 2. Deoxyribose• 3. Thymine• 4. Never leaves nucleus

B. RNA• 1. Single stranded• 2. Ribose• 3. Uracil• 4. Enter & leave nucleus

X. Why Proteins are Important

• A. Remember proteins are created from your DNA sequence which are your genes.– 1. the sequence will identify the protein being made that

protein can regulate chemical reactions & catalyze others. (primary structure)• Ex. Enzyme the produces color pigment in a flower or proteins

that regulate growth

• Primary structure – amino acid sequence

• Secondary structure – twisting of chain either by coiling (a-helix) or zigzagging (beta-pleated sheets)

• Tertiary structure – folding into 3 dimensional pattern

• Quaternary structure – when 2 or more polypeptides get together

• Chaperones help with this process