Sintesis Protein | Transkripsi

Protein Synthesis and Transcription

Protein synthesis is the process by which genetic information in DNA is used to produce proteins. The overall pathway—DNA → RNA → protein—is known as the central dogma. This summary focuses mainly on transcription.

Why Protein Synthesis Matters

Proteins perform many roles in living organisms. They act as enzymes and hormones and help form body structures.

Changes in DNA can affect the RNA and proteins produced. For example, a mutation may disrupt pigment production and result in an albino organism.

Where the Process Happens

• Prokaryotic cells lack a nuclear membrane, so transcription and translation both occur in the cytoplasm.
• Eukaryotic cells have a nucleus. Transcription occurs in the nucleus, while translation occurs in the cytoplasm at ribosomes.

DNA Strands and Transcription

DNA consists of two antiparallel strands:

• The template strand, also called the antisense or non-coding strand, is used to make RNA.
• The coding strand, also called the sense strand, has a sequence similar to the resulting RNA.

RNA polymerase reads the template strand in the 3′ to 5′ direction and builds RNA in the 5′ to 3′ direction. The RNA sequence is complementary to the template strand and resembles the coding strand, except RNA uses uracil (U) instead of DNA’s thymine (T).

During translation, mRNA is read in groups of three bases called codons. Each codon corresponds to an amino acid, and the amino acids are joined to build a protein.

Main Stages of Transcription

1. Initiation: RNA polymerase binds to a DNA region called the promoter, which signals where transcription begins.
2. Elongation: RNA polymerase moves along the template strand and adds RNA nucleotides, lengthening the RNA molecule.
3. Termination: When the enzyme reaches a terminator sequence, transcription stops and the RNA transcript is released.

Eukaryotic RNA Processing

In eukaryotes, the first transcript is pre-mRNA. It must be processed before it can be used in translation.

• Splicing: A spliceosome removes introns, which are segments not retained in the final message, and joins exons, which are retained.
• 5′ cap and poly-A tail: A cap is added to the 5′ end, and a stretch of adenine nucleotides called the poly-A tail is added to the 3′ end. These modifications help protect and identify mature mRNA and prepare it for use in the cytoplasm.

Translation is the next stage of protein synthesis; its detailed explanation is left for a later video.

Speakers and Sources

• Presenter: Host from the Kak Bio channel
• Other speakers: None identified