GEN BIO 2 | Protein Synthesis

Protein Synthesis

Genes along the DNA molecule can direct synthesis of RNA as it aids the in the synthesis of polypeptides in forming proteins.

mRNA | Full Name

Messenger RNA

mRNA | Definition

carries information that specifies a protein

rRNA | Full Name

Ribosomal RNA

rRNA | Definition

forms the ribosome where the site of protein synthesis occurs

tRNA | Full Name

Transfer RNA

tRNA | Definition

carries amino acid to the ribosome

Transcription

the process in the nucleus in which a gene’s DNA sequence is copied/transcribed to make the mRNA molecule through the attachment of free RNA bases

Base Pairings in Transcription

• Cytosine and Guanine pair with each other.

• Adenine pairs with Uracil.

• Thymine Pairs with Adenine.

Steps in Transcription

1. Initiation

2. Elongation

3. Termination

Initiation in Transcription

The enzyme RNA polymerase binds to the region of a gene called the promoter. The DNA unwinds to expose the nucleotides so the RNA polymerase can read it and make a complementary sequence of bases.

Elongation in Transcription

The RNA strand lengthens as the RNA polymerase adds the RNA nucleotides in a 5’ to 3’ direction.

Termination in Transcription

RNA polymerase reaches the terminator gene, signalling the release of a new mRNA strand and the removal of the enzyme to the DNA template.

Introns

junk sequences that is not needed by the protein and can cause errors

Exons

the good sequences

mRNA Processing

• In this nucleus process between transcription and translation, a 5’ cap is added to the beginning of the RNA while a poly-A tail is added to the end of it.

• Both of these additions secure the RNA sequence while it matures before entering t.

• The introns are also chopped out as the exons are joined together.

Spliceosome

what removes the introns from the mRNA

codon

the triplet code in mRNA that indicates the creation of a certain amino acid

Movement of mRNA

it moves out of the nucleus and into the cytoplasm

Translation

the process in the cytoplasm where the genetic code in the mRNA is read to make a protein; it requires all three RNAs, amino acids, and enzymes. The RNA enters the ribosome.

Stages of Translation

1. Initiation

2. Elongation

3. Termination

The Parts of the tRNA

one end of the tRNA has an anticodon while the other end contains the amino acid specified by the codon

anti-codon

the triplet codes in the tRNA that complement the bases in the mRNA

Large Subunit

where the sites are located

E site

known as the exit site, how the tRNA exits the large subunit

P Site

also known as the peptidyl site, this is where the peptide bonds are created; the first tRNA goes to this site

A site

• also known as the aminoacyl site, this is where the amino acid is created

• the polypeptide chain attached to the tRNA in the P site transfers to the amino acid of this chain in the tRNA in this site to lengthen the amino acid chain

Initiation in Translation

• the small ribosomal subunit attaches to the mRNA in the vicinity of the start codon or (AUG).

• An anticodon (UAC) of a tRNA carries the start amino acid methionine or Met that pairs with the mRNA codon

• The large ribosomal subunit joins to the small subunit

Methionine

the starting amino acid or start codon

Elongation in Translation

The polypeptide chain increases in length one amino acid at a time

• A new tRNA enters the site.

• The tRNA at the P site transfers its amino acid to the tRNA in the A site.

• The ribosome moves forward as the tRNA from the P site moves to the E site and exits the area.

• The tRNA in the A site moves to the P site.

Termination in Translation

• a stop codon appears at the A site (UAG, UAA, UGA)

• The protein complex known as the release factors binds tot he stop codon and cleaves the polypeptide from the last tRNA.

• This creates a functional protein.

How many amino acids are involved in protein synthesis?

20