Download General Biology DNA Structure and more Summaries Biology in PDF only on Docsity! General Biology : Written Work #1 Lesson 1.1 ➢ Structure of DNA (Deoxyribonucleic acid) ○ Nucleic acid ○ Deoxyribose is a sugar ○ Double-stranded ○ Double helix shaped ○ Antiparallel with 5’ and 3’ ends ○ 4 nitrogenous basis code: - Adenine and Thymine - Guanine and Cytosine ○ Found in nucleus ➢ Ribonucleic acid (RNA) ○ Similar to DNA but contains ribose rather than deoxyribose sugar ○ Single-stranded ○ Types of RNA : - Messenger RNA (mRNA): carries the “message” of the DNA to the cytoplasm of cells where protein is made in amino acid sequence specified by the mRNA - Transfer RNA (tRNA): short-chain type that transfers/carries specific amino acids to form protein with specific amino acid arrangement dictated by DNA. - Ribosomal RNA (rRNA): a component of ribosomes. A non-specific site for making polypeptides. ○ 4 nitrogenous basis code: - Adenine and Uracil - Guanine and Cytosine DNA vs RNA ○ Nitrogenous bases: - Pyrimidines - cytosine, thymine and uracil have a single six-membered ring - Purines - adenine and guanine have a six-member ring fused to a five-membered ring DNA RNA Monosaccha ride (sugar) The monosacchari de is D-2-deoxyri bose, an aldopentose that lacks a hydroxyl group at C2 The monosacchari de is aldopentose D-ribose Nitrogenous bases Contains the bases A,G,C and T Contains the bases A,G,C and U ➢ DNA replication 1. Helicase unwinds the parental double helix. 2. Molecules of single strand binding protein stabilize the unwound template strands. 3. The leading strand is synthesized continuously in the 5′ to 3′ direction by DNA pol III. 4. Primase begins synthesis of the RNA primer for the fifth Okazaki fragment. 5. DNA pol III is completing synthesis of fragment 4. When it reaches the RNA primer on fragment 3, it will detach and begin adding DNA nucleotides to the 3′ end of the fragment 5 primer in the replication fork. 6. DNA pol I removes the primer from the 5′ end of fragment 2, replacing it with DNA nucleotides added one by one to the 3′ end of fragment 3. After the last addition, the backbone is left with a free 3’ end. 7. DNA ligase joins the 3’ end of fragment 2 to the 5’ end of fragment 1. ➢ DNA Proofreading and Repair ○ Proofreading by DNA Polymerases: - DNA polymerases proofread newly synthesized DNA, replacing any incorrect nucleotides to maintain DNA fidelity. ○ DNA Repair Mechanisms: - DNA repair mechanisms, including mismatch repair and nucleotide excision repair, correct errors and damage in DNA to prevent the accumulation of mutations. Lesson 1.2 ➢ DNA Transcription ○ Initiation: - RNA polymerase binds to the promoter region of the DNA molecule, marking the beginning of transcription. ○ Elongation: - RNA polymerase synthesizes a complementary RNA strand using one of the DNA strands as a template, elongating the RNA chain. ○ Termination: - Transcription terminates when RNA polymerase reaches a termination signal in the DNA sequence, causing RNA polymerase and the newly formed RNA transcript to dissociate from the DNA. ➢ DNA Translation ○ Initiation: - The small ribosomal subunit binds to the mRNA at the start codon, recruiting the initiator tRNA carrying methionine, followed by the joining of the large ribosomal subunit to form the initiation complex. ○ Elongation: - A new tRNA carrying the appropriate amino acid binds to the next codon on the mRNA, catalyzing the formation of a peptide bond between adjacent amino acids, while the ribosome moves along the mRNA, repeating the process until a stop codon is reached. ○ Termination: - When a stop codon is encountered, a release factor binds to the A site of the ribosome, triggering the release of the polypeptide chain and disassembly of the ribosome complex. ○ Protein Folding and Post-translational Modifications: - After translation, the newly synthesized polypeptide undergoes folding into its functional conformation, assisted by chaperone proteins, and may undergo post-translational modifications such as glycosylation, phosphorylation, or cleavage, which are crucial for its final structure and function. TERMS TO REMEMBER
