Protein Synthesis and Genetic Code Overview

Overview of Key Concepts

Learning Objectives

• Explain the steps of protein synthesis, including transcription and translation:
  Protein synthesis occurs in two main stages: transcription and translation.

  1. Transcription:

  • The process of copying genetic instructions from DNA to form messenger RNA (mRNA).

  • During transcription, DNA unwinds and a complementary strand of mRNA is synthesized.

  • The mRNA then exits the nucleus and enters the cytoplasm.

  1. Translation:

  • In this stage, the mRNA is translated into a sequence of amino acids.

  • Ribosomes read the sequence of the mRNA, while transfer RNA (tRNA) brings the corresponding amino acids to the ribosome to form a protein.

• Describe the basic structure of DNA:
  DNA, or deoxyribonucleic acid, is usually a long, threadlike molecule composed of two strands that form a double helix.

  • Each strand is made of nucleotides, which include:

  • One sugar (deoxyribose)

  • One phosphate group

  • One nitrogenous base (Adenine, Thymine, Cytosine, or Guanine)

  • In human cells, there are typically 46 DNA molecules found in the nucleus.

• Compare and contrast DNA and RNA molecules:
  DNA and RNA differ in several critical ways:

  • Structure:

  • DNA is a double-stranded molecule, while RNA is single-stranded.

  • Sugar:

  • The sugar in DNA is deoxyribose, while the sugar in RNA is ribose.

  • Nitrogenous bases:

  • DNA contains thymine (T), whereas RNA contains uracil (U).

  • Function:

  • DNA stores genetic information, while RNA plays a role in protein synthesis.

• Describe and use the genetic code identifying start and stop codons:
  The genetic code is made up of sequences of nucleotides that specify which amino acids will be added during protein synthesis.

  • Start Codon:

  • The start codon (AUG) initiates the translation process, signaling the beginning of protein synthesis.

  • Stop Codons:

  • Stop codons (UAA, UAG, UGA) terminate the translation, signaling the release of the newly formed protein.

  • By identifying these codons within mRNA, students can understand the signals for starting and completing protein synthesis.

• Focus: Central Dogma of molecular biology.

DNA and its Structure

• DNA (Deoxyribonucleic Acid)

  • Long, threadlike molecule with a uniform diameter and varied length.

  • Typically, 46 DNA molecules are found in the nucleus of most human cells.

  • Composed of nucleotides which are polymers consisting of:

  • One sugar

  • One phosphate group

  • One nitrogenous base.

Functions of DNA

• Two Major Functions:

  1. Self Replication (DNA -> DNA)

  • Mechanism for passing hereditary information from generation to generation.

  1. Protein Synthesis (DNA > RNA > Proteins)

  • All proteins are synthesized based on the genetic instructions in DNA.

Comparing RNA and DNA

• RNA vs. DNA:

  • RNA is a smaller single-strand molecule compared to the double-stranded structure of DNA.

  • Types of RNA:

  • mRNA (Messenger RNA): Carries genetic information from DNA.

  • rRNA (Ribosomal RNA): Forms the structure of ribosomes.

  • tRNA (Transfer RNA): Delivers amino acids to ribosomes.

  • Differences include:

  • Sugar in RNA is ribose instead of deoxyribose in DNA.

  • Uracil in RNA replaces thymine in DNA.

Protein Composition and Functions

• Proteins

  • Made up of amino acids (20 different types).

  • Major roles in the body:

  • Building new cells and repairing tissues.

  • Enzyme and hormone production.

  • Antibody formation for immune defense.

  • Energy production.

Types of Proteins

• Immune Proteins:

  • Antibodies and complement system proteins.

• Muscle Proteins:

  • Actin and myosin, providing muscle movement.

• Blood Proteins:

  • Hemoglobin (transports oxygen), fibrinogen (clots blood), albumin (regulates liquid levels).

• Structural Proteins:

  • Keratin (skin, hair, nails), collagen (strength), elastin (flexibility).

• Enzymes and Membrane Proteins:

  • Aid digestion, facilitate transport across membranes, and act as receptors.

The Process of Protein Synthesis

• Transcription:

  • The process of copying genetic instructions from DNA to form mRNA.

  • mRNA exits the nucleus to enter the cytoplasm.

• Translation:

  • Converts the sequence of mRNA into a sequence of amino acids, forming a protein.

  • Occurs at ribosomes where tRNA brings amino acids to mRNA.

Cracking the Genetic Code

• DNA to RNA base pairing:

  • Adenine (A) pairs with Uracil (U) in RNA, Thymine (T) pairs with Adenine (A), Cytosine (C) pairs with Guanine (G).

Practice Questions

• Review understanding of nucleotides and the processes of transcription and translation with multiple-choice questions.