Nucleotides – Are Compounds Containing Base, Sugar And Phosphate Group

NUCLEOTIDES – are compounds containing BASE, SUGAR and PHOSPHATE GROUP FUNCTIONS: o For production of nucleic acid o Intermediate substance for metabolic process o Regulatory substance for coenzymes o Energy currency of the cell (ATP) o Regulates some process in metabolism

I. BASE PURINE RN A DN A

ADENINE GUANINE ADENINE GUANINE

PYRIMIDIN E CYTOSINE URACIL CYTOSINE THYMINE

II. SUGAR – PENTOSE o RIBOSE  Has HYDROXYL  Carbon #2 o DEOXYRIBOSE  Remove HYDROXYL

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C1 – attachment to BASE

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C5 – attachment to PHOSPHATE GROUP

C2 – attachment to HYDROXYL GROUP

SUGAR + BASE = NUCLEOSIDE III. o o o

PHOSPHATE GROUP MONOPHOSPHATE DIPHOSPHATE TRIPHOSPHATE

ESTER BONDS o Stabilizes the phosphate groups o Found between phosphates o Has high energy bonds at phosphate groups NUCLEIC ACIDS o a chain of nucleotides linked by ester bonds o group of nucleotides linked by phosphodiester bonds at C3 and C5 NUCLEASE o an enzyme that destroys phosphodiester bonds o ENDONUCLEASE – inside cleaving (middle) o EXONUCLEASE – outside cleaving (ends)

DNA (DOUBLE HELIX) o A chain of many nucleotides o DEOXYRIBOSE (A, G, C,T) o Contains genetic information o Has 2 nucleotide chains arranged in a double helix in a right handed turn B-DNA (WATSON & CRICK DNA) o Most common type of DNA o Described by Watson and Crick PHOSPHATE-SUGAR BACKBONE o HYDROPHOBIC o Found outside the helix BASE o HYDROPHILIC o Located inside the helix CHARACTERISTICS OF DNA: 1. ANTIPARALLEL – opposite direction 2. COMPLEMENTARY – bases complement each other 3. H-BONDS – links the complementary bases o DENATURING H-BONDS  Altering pH  High temperature – most commonly used for denaturing DNA 4. MELTING POINT – the temperature at which 50% of the DNA strand is separated 5. RENATURATION – done simply by cooling CENTRAL DOGMA OF MOLECULAR BIOLOGY o Simply expresses how proteins are derived from DNA DNA (REPLICATION) -> RNA (TRANSCRIPTION) -> PROTEIN (TRANSLATION) DNA REPLICATION – occurs in S PHASE TRANSCRIPTION & TRANSLATION – can occur in either G1 or G2 PHASE STEPS IN DNA REPLICATION: 1. Determine the origin of replication o DNA a PROTEIN – determines the origin of replication by binding to the site of replication o PROKARYOTES – single origin of replication o EUKARYOTES – multiple origins of replication 2. Separation of the double strands by the enzyme HELICASE 3. SINGLE STRAND BINDING PROTEINS (SSBP) – prevents the 2 strands from coiling again and protects the single strands from NUCLEASE (degradation)

4. Relaxation of super coils by the enzyme DNA GYRASE/DNA TOPOSIOMERASE 5. DNA-DEPENDENT RNA POLYMERASE o RNA PRIMER – important in beginning the DNA replication o DNA is read in the 3’-5’ sequence 6. DNA POLYMERASE – extends the strand 7. DNA POLYMERASE III – proof-reading from 3’-5’ (exonuclease activity) 8. DNA POLYMERASE I – lengthens the DNA chain and removes the RNA primer (5’-3’ exonuclease activity) o Lengthening of the replication is towards the replication fork LEADING STRAND – towards the replication fork LAGGING STRAND – away from the replication fork OKAZAKI FRAGMENTS – fragments that are not continuous DNA LIGASE – enzyme that combines the okazaki fragments

-Rosette Go 080808 