🔬General Biology I Unit 15 – Genes and Proteins

Key Concepts

• Genes contain instructions for making proteins, which are essential for the structure and function of all living organisms
• DNA (deoxyribonucleic acid) is the hereditary material that stores genetic information in the form of a double helix
• RNA (ribonucleic acid) acts as a messenger, carrying genetic information from DNA to ribosomes for protein synthesis
• Transcription is the process of copying genetic information from DNA to RNA
• Translation is the process of synthesizing proteins using the genetic information carried by RNA
• Gene expression is the process by which genetic information is used to synthesize functional gene products, such as proteins
• Genetic mutations are changes in the DNA sequence that can lead to variations in traits and sometimes genetic disorders
• Biotechnology utilizes genetic engineering techniques to modify organisms for various applications (agriculture, medicine, research)

DNA Structure and Function

• DNA is composed of four nucleotide bases: adenine (A), thymine (T), guanine (G), and cytosine (C)
• Nucleotides are joined together by phosphodiester bonds to form a polynucleotide chain
• DNA exists as a double helix, with two complementary strands held together by hydrogen bonds between base pairs
  • A always pairs with T, and G always pairs with C
• The sugar-phosphate backbone of DNA is on the outside of the double helix, while the nitrogenous bases are on the inside
• DNA replication is the process of making an identical copy of the original DNA molecule
  • Replication is semiconservative, meaning each new DNA molecule contains one original strand and one newly synthesized strand
• DNA packaging involves histones and other proteins that help condense and organize DNA within the nucleus
• The primary function of DNA is to store and transmit genetic information across generations

RNA and Transcription

• RNA is similar to DNA but contains the sugar ribose instead of deoxyribose and the base uracil (U) instead of thymine (T)
• There are three main types of RNA: messenger RNA (mRNA), transfer RNA (tRNA), and ribosomal RNA (rRNA)
  • mRNA carries genetic information from DNA to ribosomes for protein synthesis
  • tRNA transports amino acids to ribosomes and matches them to the appropriate codons in mRNA
  • rRNA is a component of ribosomes and plays a role in protein synthesis
• Transcription begins with the binding of RNA polymerase to a promoter region on the DNA template strand
• RNA polymerase unwinds the DNA double helix and synthesizes a complementary RNA strand using the DNA template
• Transcription ends when RNA polymerase reaches a terminator sequence, and the newly synthesized RNA is released
• In eukaryotes, the primary transcript (pre-mRNA) undergoes processing, including the addition of a 5' cap and a 3' poly-A tail, and splicing to remove introns

Protein Structure and Synthesis

• Proteins are essential macromolecules that perform a wide range of functions in living organisms (enzymes, structural components, hormones)
• Amino acids are the building blocks of proteins and are joined together by peptide bonds to form polypeptide chains
• The sequence of amino acids in a protein determines its unique three-dimensional structure and function
• Protein synthesis (translation) occurs at ribosomes and involves the decoding of mRNA codons into amino acids
  • Codons are three-base sequences on mRNA that specify particular amino acids or signal the start or stop of translation
• tRNAs, with their anticodons, base pair with the codons on mRNA to ensure the correct amino acids are added to the growing polypeptide chain
• The newly synthesized polypeptide chain undergoes folding and may require post-translational modifications to become a fully functional protein
• Chaperone proteins assist in the proper folding of newly synthesized proteins

Gene Expression and Regulation

• Gene expression is the process by which genetic information is used to synthesize functional gene products, such as proteins
• Prokaryotic gene expression is primarily regulated at the transcriptional level through the action of transcription factors and operons
  • Operons are clusters of genes that are transcribed together and regulated by a single promoter (lac operon, trp operon)
• Eukaryotic gene expression is regulated at multiple levels, including transcriptional, post-transcriptional, translational, and post-translational
  • Transcriptional regulation involves the binding of transcription factors to regulatory sequences (enhancers, silencers) to control gene expression
  • Post-transcriptional regulation includes mRNA processing, stability, and transport
  • Translational regulation involves the control of protein synthesis at the ribosome
  • Post-translational regulation includes protein modifications, such as phosphorylation or glycosylation, that can affect protein function
• Epigenetic modifications, such as DNA methylation and histone modifications, can also influence gene expression without changing the DNA sequence

Genetic Mutations and Variation

• Mutations are changes in the DNA sequence that can occur spontaneously or be induced by environmental factors (UV radiation, chemicals)
• Point mutations involve the change of a single nucleotide and can be classified as silent, missense, or nonsense mutations
  • Silent mutations do not change the amino acid sequence of the protein
  • Missense mutations result in the substitution of one amino acid for another
  • Nonsense mutations introduce a premature stop codon, leading to a truncated protein
• Frameshift mutations occur when nucleotides are inserted or deleted, shifting the reading frame and altering the amino acid sequence
• Chromosomal mutations involve larger-scale changes, such as deletions, duplications, inversions, or translocations of DNA segments
• Genetic variation arises from mutations and recombination events and is essential for adaptation and evolution
• Single nucleotide polymorphisms (SNPs) are common variations in the DNA sequence that can be used as genetic markers

Applications in Biotechnology

• Genetic engineering involves the manipulation of an organism's genetic material to modify its characteristics or produce desired products
• Recombinant DNA technology allows the insertion of foreign DNA into a host organism to express specific genes (insulin production in bacteria)
• Polymerase chain reaction (PCR) is a technique used to amplify specific DNA sequences for analysis or manipulation
• DNA sequencing technologies enable the determination of the precise order of nucleotides in a DNA molecule
• Gene therapy is an experimental technique that aims to treat genetic disorders by introducing functional copies of genes into cells
• Genetically modified organisms (GMOs) are organisms whose genetic material has been altered using genetic engineering techniques (pest-resistant crops, disease models)
• CRISPR-Cas9 is a powerful gene-editing tool that allows precise modifications to be made to the genome of living organisms
• DNA fingerprinting is a forensic technique that uses genetic markers to identify individuals based on their unique DNA profiles

Review and Practice

• Genes are segments of DNA that encode instructions for making specific proteins
• The central dogma of molecular biology describes the flow of genetic information from DNA to RNA to proteins
• DNA replication ensures the accurate transmission of genetic information to daughter cells during cell division
• Transcription is the synthesis of RNA from a DNA template, while translation is the synthesis of proteins using the genetic code carried by mRNA
• The genetic code is the set of rules that defines how codons on mRNA are translated into amino acids
• Gene expression is tightly regulated to ensure that the right proteins are produced in the right amounts at the right times
• Mutations can have various effects on protein function, ranging from no effect to complete loss of function or gain of new functions
• Biotechnology harnesses the power of genetic engineering to develop new products, therapies, and research tools
• Understanding the structure and function of DNA, RNA, and proteins is crucial for grasping the fundamental processes of life and their applications in medicine and technology