DNA & Protein Synthesis (2024-2025) PDF

# مركز الشامل ## The DNA & Protein Synthesis **ASSIST. PROF.** **Dr. GALAL ASSAKAF** **2024-2025** - A diagram shows DNA and RNA with highlighted parts. ## The Nucleic Acids (medical history) ### Discovery of DNA - DNA was named by biochemist Johann Friedrich (1844-1895) and his student. - Fri...

# مركز الشامل ## The DNA & Protein Synthesis **ASSIST. PROF.** **Dr. GALAL ASSAKAF** **2024-2025** - A diagram shows DNA and RNA with highlighted parts. ## The Nucleic Acids (medical history) ### Discovery of DNA - DNA was named by biochemist Johann Friedrich (1844-1895) and his student. - Friedrich isolated an acidic substance rich in phosphorus from salmon sperm. - It was believed that the substance was hereditary matter of the cell, but there was no real evidence. ### The Nucleic Acid (medical history) ### Discovery of the double helix - By 1900: components of DNA were known. - By 1953: x-ray diffraction determined geometry of the DNA molecule. - The Nobel Prize awarded in 1962 to 3 men: Watson, Crick and Wilkins but not to Rosalind Franklin who died at the age of 37 due to cancer. - The x-ray data from the research of Rosalind Franklin provided the answers. # DNA (DEOXYRIBONUCLEIC ACID) ## 1. FUNCTION OF DNA - DNA codes for proteins (structural proteins, enzymes, and hormones) - Information for building proteins is carried in the sequence of nitrogen bases. - Proteins determine physical and metabolic traits and regulate growth and development. # Chromosome Organization - A chromosome is an enormous strand of super coiled DNA. - Sections of DNA (3%) on the chromosome that code for proteins are called genes. - Noncoding sections of DNA (97%)are called "junk DNA" (regulatory or unknown function). ## Chromatin Structure - A diagram shows a chromatin structure with its parts: - **Metaphase chromosome** - **Chromatid** - **Chromatin fiber** - **Supercoiled structure** - **Nucleosome** - **Histones** - **DNA** # Building Blocks of DNA - DNA is composed of **nucleotides**. - **Nucleotides contain three parts:** - 5-Carbon Sugar (deoxyribose) - Phosphate Group - Nitrogen Base (four types: adenine, guanine, thymine and cytosine) ## Structure of DNA Nucleotides - Each nucleotide consists of: - **A nitrogenous base**. - **A phosphate group.** - **A sugar** ## 1. Nitrogenous Bases - **Purines** (Adenine, Guanine): - A double carbon-nitrogen ring. - **Pyrimidines** (Cytosine, Thymine, Uracil): - A single carbon nitrogen ring. # Composition of DNA - **Chargaff showed:** - **Amount of adenine relative to guanine differs among species** - **Amount of adenine always equals amount of thymine and amount of guanine always equals amount of cytosine** - A=T and G=C # Watson-Crick Model - DNA consists of two nucleotide strands. - Strands run in opposite directions. - Strands are held together by H-bonds between bases. - A binds with T and C with G - The DNA molecule is a double helix. - A diagram shows the DNA structure with complementary base pairing and hydrogen bonds. # DNA Replication - Before a cell can divide by mitosis or meiosis, it must first makes a copy of its chromosomes. - The DNA in the chromosomes is copied in a process called DNA replication. - Without DNA replication, new cells would have only half the DNA of their parents. - It is important that the new copies are exactly like the original molecules # What is the purpose of DNA replication? - It gives daughter cells produced by cell division a complete set of genetic information identical to the parent cell. # Where replication occurs? - The nucleus. # How replication occurs? 1. Helicase enzymes open the parent strand by separating the nitrogen base pairs. 2. DNA polymeraselll pairs free DNA nucleotides with the exposed base s on both strands following the bas e pair rules. - Each strand from the parent molecule serve as a template 3. Hydrogen bonds reform spontaneously sealing the two strands of each DNA molecule together. - A diagram shows the DNA replication process, highlighting the direction of replication. # Results Of Replication - Two molecules of DNA that are identical. - Each is half old (strand from parent) and half new (strand synthesized by DNA polymerase) # Enzymes In Replication - Enzymes unwind the two strands (gyrase) Topoisomerase. - DNA polymerase III attaches complementary nucleotides and reads correct. - DNA ligase fills in the gaps between Okazaki fragments . - Enzymes wind the two strands together # Replication Fork - A diagram shows the replication fork, highlighting the two strands: - Leading strand - Lagging strand - It also shows the movement of the replication fork, the enzymes: - RNA polymerase - DNA ligase - Pol ІІ - Pol І # Protein Synthesis - Cells build proteins following instructions coded in genes (DNA). - This process consists of two parts: - **Transcription:** DNA to RNA - **Translation:** RNA to polypeptides (proteins) ## 1. Transcription DNA to RNA - **What is RNA (RIBONUCLEIC ACID)?** - Nucleic acid made by genes in the DNA, involved in the synthesis of proteins. # RNA Structure - Composed of nucleotides, but differs from DNA in three ways: - Single strand of nucleotides instead of double stranded - Has uracil instead of thymine - Contains ribose instead of deoxyribose - A diagram shows DNA and RNA with highlighted parts: - DNA - RNA - Thymine - Uracil - Ribose - Deoxyribose # RNA Function - Three forms of RNA involved in protein synthesis: - **mRNA (messenger):** copies instructions in DNA and carries these to the ribosome. - **tRNA (transfer):** **carries amino acids to the ribosome.** - **rRNA (ribosomal):** composes the ribosome. # Transcription - DNA is copied into a complementary strand of mRNA. - Why? - DNA cannot leave the nucleus. - Proteins are made in the cytoplasm. - **mRNA serves as a "messenger" and carries the protein building instructions to the ribosomes in the cytoplasm.** # Location Of Transcription - The nucleus. # How Transcription Occurs? 1. RNA polymerase untwists and unzips a section of DNA (usually a single gene) from a chromosome. 2. RNA polymerase pairs free RNA nucleotides to the exposed bases of one of the DNA strands following base pair rules. - Uracil replaces thymine. 3. Only 1 strand of DNA serves as a template, the other "hangs out". 4. Newly synthesized mRNA separates from template DNA and DNA zips back up. # Steps From DNA To Proteins - **Same two steps produce all proteins:** - **DNA is transcribed to form RNA** - Occurs in the nucleus. - RNA moves into cytoplasm. - **RNA is translated to form polypeptide chains, which fold to form proteins.** # Requeriments - A diagram shows the components of the transcription process: - duplex DNA - RNA polymerase - triphosphate ribonucleotides - ATP, CTP, GTP, UTP - Mg²⁺ - RNA ## Base Pairing Compared - A table shows the base pairing during transcription and DNA replication. # The Promoter - A base sequence in the DNA that signals the start of a gene. - For transcription to occur, RNA polymerase must first bind to a promoter. - A diagram shows the promoter with its parts: - Promoter region - Promoter # Classes of RNA - **Messenger RNA (mRNA)** - Carries protein-building instruction - **Ribosomal RNA (rRNA)** - Major component of ribosomes - **Transfer RNA (tRNA)** - Delivers amino acids to ribosomes # The Genetic Code - Set of 64 base triplets. - **Codons:** - Nucleotide bases read in blocks of three. - **61 specify amino acids.** - **3 stop translation** - A diagram shows the genetic code with codons and amino acids. # The Genetic Code - Consists of 64 triplet codons (A, G, C, U). - 4 ³= 64 - All codons are used in protein synthesis. - 3 termination (stop) codons: UAA, UAG, UGA - AUG (methionine) is the start codon (also used internally). - Multiple codons for a single amino acid. - 5 amino acids are specified by the first two nucleotides only. - 3 additional amino acids (Arg, Leu, and Ser) are specified by six different codons. - A table shows the universal genetic code. ## 2. Translation - Three Stages: - **INITIATION** - **ELONGATION** - **TERMINATION** ## Initiation - Initiator tRNA binds to small ribosomal subunit. - Small subunit/tRNA complex attaches to mRNA and moves along it to an AUG "start” codon. - Large ribosomal subunit joins complex. - A diagram shows the initiation phase of translation. ## Binding Sites On Large Subunit - A diagram shows the large subunit with the binding sites for tRNA and mRNA. ## Elongation - mRNA passes through ribosomal subunits. - tRNAs deliver amino acids to the ribosomal binding site in the order specified by the mRNA. - Peptide bonds form between the amino acids and the polypeptide chain grows. - A diagram shows the elongation phase of translation with the movement of tRNA. ## Termination - A STOP codon moves into the area where the chain is being built. It is the signal to release the mRNA transcript. - The new polypeptide chain is released from the ribosome. - It is free to join the pool of proteins in the cytoplasm or to enter rough ER of the endomembrane. - The two ribosomal subunits now. - A diagram shows the termination phase of translation with the release of mRNA. # Conclusion - The image/document is an overview of the DNA and protein synthesis, explaining the different steps involved in the process. - The document includes diagrams, tables, and definitions that further clarify the concepts. The document goes through DNA replication, transcription and translation.