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Cell structure

Cell structure. Nucleoid. Single strand of DNA, usually circular, usually looks like a big ball of messed up twine… Size – smallest organism yet discovered (Nanoarchaeum equitans) 490,889 base pairs; e. coli 4.7 Mbp, most prokaryotes 1-6 million base pairs (1-6 MBp); Humans 3300 MBp

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Cell structure

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  1. Cell structure

  2. Nucleoid • Single strand of DNA, usually circular, usually looks like a big ball of messed up twine… • Size – smallest organism yet discovered (Nanoarchaeum equitans) 490,889 base pairs; e. coli 4.7 Mbp, most prokaryotes 1-6 million base pairs (1-6 MBp); Humans 3300 MBp • DNA is around 1000 mm long in bacteria, while the organism is on the order of 1 mm long – special enzymes called gyrases help coil it into a compact form

  3. Construction, Part 3 • Bases – Two types: Pyrimidine Purine • Derivatives Cytosine, C Uracil, U Thymine, T Adenine, A Guanine, G DNA  C,T,A,G No U RNA  C,U,A,G No T

  4. dNTP’s • Deoxyribonucleotide triphohosphate • ATP (the energy-generating molecule) is the same and the ‘A’ building block – also GTP, CTP, UTP, TTP • These react to chain lengthen and form RNA or DNA – lose 2 of the PO4 groups in the process

  5. DNA is double-stranded (double helix), while RNA is single stranded • RNA has a slightly different sugar backbone – ribose instead of deoxyribose • RNA has a lot of turns and kinks, more chaotic structure, but some sections are closer to the outside than others… RNA DNA

  6. Palindromes and DNA • DNA’s structure is inherently directional • dNTP’s have bonds on opposite ends that attach  3’ (OH) and a 5’ (PO4) • Direction of the ‘code’ 3’  5’

  7. DNA enzymes • Restriction endonuclease – cuts DNA at specific base combinations • DNA ligase – links DNA molecules • DNA polymerase I – attaches DNTP’s, repairs DNA • DNA polymerase II – attaches DNTP’s, proofreads • DNA gyrase – twists, coils DNA • DNA Helicase – DNA strand separation • DNAse - degrades DNA to DNTP’s

  8. Data copying inside a cell • Polymerases – proteins that catalyze different components of DNA, RNA replication • DNA replication – occurs by unwinding, copying each strand, and putting 2 identical pairs together • Transcription – formation of RNA from DNA • Translation – formation of proteins from RNA information

  9. Transcription RNA polymeraze takes the DNA and temporarily unwinds it, templates the transfer RNA from that, using ribonucleoside triphosphates to assemble…

  10. Ribosome • The ribosome is the site of translation of messenger RNA into protein. It is composed of two subunits. • In prokaryotes, the large subunit is called 50S and the small subunit is called 30S. The 30S subunit consists of a single strand of RNA (the 16S rRNA, 1542 bases), and 21 proteins ranging in molecular weight from 9 kD to 61 kD. • The 30S subunit is the site of translation initiation. • Measured by a ‘sedimentation coefficient’ – 16S rDNA is associated with a 16S sized small subunit of the RNA translating ribosome

  11. RNA and protein construction • The nucleotide base sequence of mRNA is encoded from DNA and transmits sequences of bases used to determine the amino acid sequence of the protein. • mRNA (“Messenger RNA”) associates with the ribosome (mRNA and protein portion). • RNA (“Transfer RNA”) also required • Codons are 3 base mRNA segments that specify a certain amino acid. • Most amino acids are coded for by more than one codon. • Translation ends when ribosome reached “stop codon” on mRNA.

  12. Ribosomal RNA • Ribosomal RNA is single stranded • RNA is a single stranded nucleic acid • mRNA- messanger RNA – copies information from DNA and carries it to the ribosomes • tRNA – transfer RNA – transfers specific amino acids to the ribosomes • rRNA – ribosomal RNA – with proteins, assembles ribosomal subunits DNA is transcribed to produce mRNA mRNA then translated into proteins.

  13. Codons • 64 combinations of bases – 61 of these code for amino acids, 3 of them signal the end or start of the chain Anticodons – the opposite sequence (G-C U-A) on the transfer RNA

  14. Translation • mRNA is coded for one or more specific amino acids and moves to the ribosome to assemble amino acids into proteins • On mRNA, codons are 3 bases, coded to specific amino acids • On tRNA, the anticodon latches to the codon on the mRNA

  15. Translation = Protein Formation • The ‘code’ on mRNA determines the sequence of protein assembly • Codon-anticodon?

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