University:
Glendale Community College
Course:
BIO160 | Introduction to Human Anatomy and Physiology
Academic year:

2020
Views:

414

Pages:

7
Author:

Davon Fischer

Section 17.2: RNA Figure 17.23 Secondary Structure of RNA §Differences between DNA and RNA primary structure: §1. Ribose sugar instead of deoxyribose §2. Uracil nucleotide instead of thymine §3. RNA exists as a single strand; forms complex threedimensional structures §4. Ribozymes - catalytic properties Section 17.2: Transcription §Transcription – process of making RNA from DNA §Major control point in expression of genes and production of proteins §Template strand (antisense strand) – DNA strand that directs synthesis §RNA polymerase reads 3’ to 5’ DNA 5’-GCCATTTCCCG-3’ ß read RNA 5’-CGGGAAAUGGC-3’ §Coding strand (complementary strand) – DNA sequence will be same as RNA sequence §Sense strand – same sequence as RNA produced DNA 5’-CGGGAAATGGC-3’ Section 17.2: Transfer RNA §Transport amino acids to ribosomes for assembly (15% of cellular RNA) §Average length: 75 bases §At least one tRNA for each amino acid §Structurally look like a warped cloverleaf due to extensive intra-chain base pairing §Aminoacyl-tRNA synthetases 3’ – attaches aa to end of anticodon Figure 17.24 Transfer RNA §Anticodon allows recognition of correct mRNA codon; properly aligns amino acid for protein synthesis §tRNA loops help facilitate interactions with the correct aminoacyl-tRNA synthetases Section 17.2: Ribosomal RNA Cytoplamsic protein complexes - protein synthesis §Components of ribosomes – small and large subunits §Eukaryotic are larger (80S) with a 60S and 40S subunit ü S – sedimentation coefficient §Prokaryotic are smaller (70S) with 50S and 30S subunits §rRNA plays a role in scaffolding as well as enzymatic functions §Peptidyl transferase – peptide bond f ormation within rRNA subunits Figure 17.25 rRNA Structure Section 17.2: Messenger RNA §Carrier of genetic information from DNA to protein synthesis (approximately 5% of total RNA) §Least abundant – 5% to 10% total cellular RNA §Formed when needed; rapid turnover §Prokaryote – protein synthesis can occur while mRNA is being synthesized §Eukaryote - mRNA must leave nucleus entering cytoplasm Section 17.2: Noncoding RNA §Noncoding RNAs (ncRNAs) - do not directly code for polypeptides §Micro RNAs and small interfering RNAs – shortest; involved in the RNA-induced silencing complex §Small Nucleolar RNAs (snoRNAs) facilitate chemical modifications to rRNA in the nucleolus §Small interfering RNAs (siRNAs) are 21-23 nt double strandedRNAs that play a crucial role in RNA interference (RNAi) §Small nuclear RNAs (snRNAs) combine with proteins to form small nuclear ribonucleoproteins (snRNPs) and are involved in splicing Section 17.3: Viruses §Viruses lack the properties that distinguish life from nonlife (e.g., no metabolism) §Infects cell - its nucleic acid can hijack the host’s nucleic acid and protein-synthesizing machinery §Make copies of itself until it ruptures the host cell or integrates into the host cell’s chromosome §Structure of Viruses §Simple virions are composed of a capsid, which encloses nucleic acid §Most capsids are helical or icosahedral §Nucleic acid is DNA or RNA §Can be single- or double-stranded, and the single-stranded RNA viruses can be + or – (e.g. (-)-ssRNA) based on whether they are positive- or negative- sense strands §(-)-ssRNA viruses need reverse transcriptase to synthesize mRNA §More complex viruses may have a membrane envelope or have proteins that protrude from the surface, called spikes