Presentation is loading. Please wait.

Presentation is loading. Please wait.

Lecture 2 Properties and functions of nucleic acids BB10006 – MVH Reference: Chapter 28 (2e) or 29 (3e) Biochemistry by Voet and Voet.

Similar presentations


Presentation on theme: "Lecture 2 Properties and functions of nucleic acids BB10006 – MVH Reference: Chapter 28 (2e) or 29 (3e) Biochemistry by Voet and Voet."— Presentation transcript:

1 Lecture 2 Properties and functions of nucleic acids BB10006 – MVH Reference: Chapter 28 (2e) or 29 (3e) Biochemistry by Voet and Voet

2 learning objectives 1) Understand the C-value paradox? 2) Be able to describe how the different helical topologies of DNA contribute to packing? 3) Understand the factors that contribute to the stability of the DNA double helix? 4) Appreciate the diverse functions of nucleic acids

3 C-value paradox DNA topology and function Factors that stabilise DNA a) denaturation and renaturation b) Sugar-phosphate chain conformations c) Base pairing and base stacking d) hydrophobic and ionic interactions Functions of nucleic acids Lecture 2: Outline

4 Size of nucleic acids Largest known mammalian gene is Dystrophin gene (DMD) 2.5 Mbp (0.1% of the genome) DNA molecules tend to be larger than RNA

5 genome sizes organism Number of base pairs (kb) viruses Lambda bacteriophage ( λ)48.6 bacteria Eschericia coli4,640 eukaryotes Yeast13,500 Drosophila165,000 Human3.3 x 10 6

6 Comparative genome sizes Why is there a discrepancy between genome size and genetic complexity?

7 C-value paradox Due to the presence of Repetitive DNA (nonfunctional?) Repetitive DNA families constitute nearly one-half of genome (~52%) Protein domains contribute to organism complexity

8 Topology of DNA DNA supercoiling: coiling of a coil Important feature in all chromosomes Supercoiled DNA moves faster than relaxed DNA Allows packing / unpacking of DNA

9 negatively supercoiled (right handed) Results from under or unwinding Important in DNA packing/unpacking e.g during replication/transcription positively supercoiled (left handed) Results from overwinding Also packs DNA but difficult to unwind

10

11 supercoiled Relaxed circle Full length linear Why does a plasmid that has never been cut give more than one band on a gel? EBr

12 Forces stabilising nucleic acid structures Applications in polymerase chain reaction (PCR) A) Denaturation and renaturation of DNA

13 Denaturation of DNA Also called melting Occurs abruptly at certain temperatures Tm – temp at which half the helical structure is lost

14 DNA melting curve

15 Tm varies according to the GC content High GC content - high Tm GC rich regions tend to be gene rich

16 Renaturation of DNA Also called annealing Occurs ~ 25 o C below Tm Property used in PCR and hybridisation techniques

17

18 Forces stabilising nucleic acid structures B) Sugar-phosphate chain conformations

19 Fig: Voet and Voet position on N-glycosidic linkage Sugar ring pucker C2 or C3 pucker Endo conformation (same side as C5) B-DNA is C2 endo

20 Forces stabilising nucleic acid structures Holds together double stranded nucleic acids Hydrogen bonds do not stabilise DNA C) Base pairing

21 Hoogsteen base pairing Watson-Crick base pairing

22 Forces stabilising nucleic acid structures D) Base stacking and hydrophobic interactions

23 Under aqueous conditions, Bases aggregate due to the stacking of planar molecules This stacking is stabilised by hydrophobic forces

24 Forces stabilising nucleic acid structures Tm of a DNA duplex increases with cationic concentration Caused by electrostatic shielding of anionic phosphate groups e.g. Mg 2+ more effective than Na + E) Ionic interactions

25 Functions of nucleic acids 1) Storage of genetic information 2) Storage of chemical energy e.g. ATP 3) Form part of coenzymes e.g. NAD +, NADP +, FAD and coenzyme A 4) Act as second messengers in signal transduction e.g. cAMP

26 Functions of nucleic acids 1) Storage of genetic information

27 DNA (deoxyribonucleic acid) DNA is the hereditary molecule in almost all cellular life forms. It has 2 main functions replication (making 2 copies of the genome) before every cell division transcription: process of copying a portion of DNA gene sequence into a single stranded messenger RNA (mRNA)

28 RNA (ribonucleic acid) Has a more varied role. 4 main types of RNA are 1)mRNA: directs the ribosomal synthesis of polypeptides and other types of RNA (translation) 2)Ribosomal RNA: have structural & functional roles 3)Transfer RNA: deliver amino acids during protein synthesis 4)Ribonucleoproteins: take part in post transcriptional processing

29 Functions of nucleic acids 2) Storage of chemical energy e.g. ATP

30 ATP (adenosine triphosphate) Involved in 1) Early stages of nutrient breakdown 2) Physiological processes 3) Interconversion of nucleoside triphosphates

31 Functions of nucleic acids 3) Form part of coenzymes e.g. NAD +, NADP +, FAD and coenzyme A

32 CoA (coenzyme A)

33 Functions of nucleic acids 4) Act as second messengers in signal transduction e.g. cAMP

34 cAMP (cyclic Adenosine Mono Phosphate) Primary intracellular signalling molecule (second messenger system) Glycogen metabolism cAMP dependent kinase (cAPK) Gluconeogenesis Fatty acid metabolism - thermogenesis

35


Download ppt "Lecture 2 Properties and functions of nucleic acids BB10006 – MVH Reference: Chapter 28 (2e) or 29 (3e) Biochemistry by Voet and Voet."

Similar presentations


Ads by Google