Lecture 2 Properties and functions of nucleic acids - PowerPoint PPT Presentation

Loading...

PPT – Lecture 2 Properties and functions of nucleic acids PowerPoint presentation | free to download - id: 6adb44-YjhjY



Loading


The Adobe Flash plugin is needed to view this content

Get the plugin now

View by Category
About This Presentation
Title:

Lecture 2 Properties and functions of nucleic acids

Description:

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

Number of Views:7
Avg rating:3.0/5.0
Date added: 14 August 2019
Slides: 36
Provided by: bssmvh
Learn more at: http://www.bath.ac.uk
Category:

less

Write a Comment
User Comments (0)
Transcript and Presenter's Notes

Title: Lecture 2 Properties and functions of nucleic acids


1
Lecture 2 Properties and functions of nucleic
acids
Reference Chapter 28 (2e) or 29
(3e) Biochemistry by Voet and Voet
BB10006 MVH
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
Lecture 2 Outline
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
4
Size of nucleic acids
DNA molecules tend to be larger than RNA
  • Largest known mammalian gene is
  • Dystrophin gene (DMD)
  • 2.5 Mbp (0.1 of the genome)

5
genome sizes
 
organism Number of base pairs
(kb)
viruses Lambda bacteriophage (
?) 48.6 bacteria Eschericia coli 4,640 eukaryot
es Yeast 13,500 Drosophila 165,000 Human
3.3 x 106
 
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
Allows packing / unpacking of DNA
Supercoiled DNA moves faster than relaxed 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
(No Transcript)
11
Why does a plasmid that has never been cut give
more than one band on a gel?
Full length linear
Relaxed circle
supercoiled
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 25oC below Tm
  • Property used in PCR and hybridisation techniques

17
(No Transcript)
18
Forces stabilising nucleic acid structures
  • B) Sugar-phosphate chain conformations

19
position on N-glycosidic linkage
Sugar ring pucker
C2 or C3 pucker Endo conformation (same side as
C5) B-DNA is C2 endo
Fig 28-18 Voet and Voet
20
Forces stabilising nucleic acid structures
  • Holds together double stranded nucleic acids
  • Hydrogen bonds do not stabilise DNA

C) Base pairing
21
Watson-Crick base pairing
Hoogsteen 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
  • mRNA directs the ribosomal synthesis of
    polypeptides and other types of RNA (translation)
  • Ribosomal RNA have structural functional
    roles
  • Transfer RNA deliver amino acids during protein
    synthesis
  • 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
(No Transcript)
About PowerShow.com