Sintesis De Proteina

RNA and Protein Synthesis
Chapter 8 Sections 4 - 7

3 main differences between RNA and DNA: 1. Sugar in RNA is ribose; Sugar in DNA is deoxyribose 2. RNA is single stranded; DNA is double stranded

3. RNA contains uracil in place of thymine

3 Types of RNA
1. Messenger RNA (mRNA)- disposable copy of DNA to carry instructions to assemble proteins at the ribosome

2. Ribosomal RNA(rRNA)- RNA inside the ribosome to make the ribosome exist
3. Transfer RNA (tRNA)- transfers amino acids in the cytoplasm to the growing polypeptide chain in the ribosomes to construct proteins

Protein Synthesis is the process of converting mRNA into a protein. It is the process of how proteins are made. Protein Synthesis has 2 steps:

1. Transcription -takes place in nucleus
2. Translation-takes place in ribosome

Transcription converts a DNA gene into a single-stranded mRNA molecule. In other words, Transcription is a process that copies DNA to make a strand of mRNA. Takes place in Nucleus.

Transcription begins at specific locations on DNA called promoters. Enzyme called RNA Polymerase separates DNA strand by breaking H bonds between nucleotide pairs. Separated strands of DNAare used as templates to assemble strand of mRNA.

RNA Polymerase start site

nucleotides DNA Templates

Nucleotides pair with one template strand of DNA. RNA polymerase bonds the nucleotides back together. The DNA helix winds again as the gene is transcribed

mRNA DNA

RNA Polymerase

Nucleotides

RNA polymerase moves along the DNA

The mRNA strand detaches from the DNA once thegene is transcribed. It will leave the nucleus to find a ribosome floating in the cytoplasm or find a ribosome on the Rough ER. This event marks the end of Transcription and the beginning of Translation.

mRNA

Transcription Overview

The transcription process is similar to replication.
• Transcription and replication both involve complex

enzymes and complementary base pairing. • Thetwo processes have different end results.
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Replication copies all the DNA; transcription copies a gene. Replication makes one copy; transcription can make many copies.

one gene

growing RNA strands

DNA

Translation converts mRNA into a protein. This process involves translating the language of nucleic acids (base sequences) into a language of proteins (amino acids). A genecarries a code to make one protein. A gene can be anywhere from 300 to 3000 base pairs long. Code written in language with only 4 “letters”: A, C, G, U

Code read 3 letters at a time (each 3 letter “word” known as a codon) to make an amino acid.
codon for methionine (Met) codon for leucine (Leu)

***Amino acids are the building blocks of proteins.

Steps to Translation:
1. mRNA leavesnucleus and attaches to ribosome.

2. Translation begins with tRNA in ribosome binding to AUG, the start codon, which signals the ribosome to assemble amino acids in a polypeptide chain to create a protein.

3. Each tRNA has an anticodon whose bases are complementary to the codon on mRNA. tRNA brings amino acids to ribosomes and build a polypeptide chain, which creates a protein.

anticodoncodon

4. Ribosome moves along mRNA, and bind new tRNA molecules to mRNA codons and link amino acids together to create a polypeptide chain.

5. The now empty tRNA molecule exits the ribosome. 6. A complementary tRNA molecule binds to the next exposed codon.

7. The polypeptide chain grows until tRNA reaches 1 of the 3 stop codons (UGA, UAA, UAG). At the end of translation, the protein isreleased, folded into a 3D structure, transported in a vesicle to the Golgi Apparatus to be modified and “shipped” to its final destination within the cell or outside of the cell.
Protein molecule

stop codon

The Genetic Code is the language of mRNA. tRNA translates this 4 letter language into amino acids, so a protein can be created. You read 3 letters at time. Example: AUG CCC GGG AUU...