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DNABook: Biochemistry, 2nd Edition by Miesfeld, McEvoy
Introduction
Chemical groups are organised into BIOMOLECULES, four major types in nature- Amino acids
- Nucleotide
- Simple sugars
- Fatty Acids
Higher- order structures of biomolecules form MACTOMOLECULES- can be chemical polymers- Proteins- polymers of
amino acids, Nucleic Acids- polymers of nucleotides or Polysaccharides- cellulose, amylose, glycogen- polymers of
carbohydrate glucose
Triacylglycerols are lipid macromolecules- formed by COVALENT LINKAGE of three fatty acids of glycerol
Organisation of macromolecules and enzyme into METABOLIC PATHWAYS- pathways enable cells to coordinate and
control complex biochemical processes for available energy
Glucose metabolism- glycolysis and gluconeogenesis
Energy conversion- citrate cycle
Fatty acid metabolism- fatty acid oxidation and biosynthesis
Metabolic pathways function within membrane- bound organelles and cellular compartments. Membranes create
AQUEOUS MICROENVIRONMENTS within cell for biochemical reactions involving metabolites and macromolecules
Translation
Replicatio
Transcripti
DNA- The Genetic Material
n
on
DNA →RNA→ Proteins
- Metabolism, Structure, Function, Organisation, Regulation, Development
Particular gene may be active in different tissues at different times
Nucleotide- composed of nitrogenous base, five-carbon ribose/ deoxyribose sugar, and one or more phosphate
groups
Nucleoside- consists of base and sugar
DNA as the molecule that contains genetic information
DeoxyriboNucleic Acid – discovered in 1869 in cell nucleus by Friedrich Miescher- found acid molecules rich in
phosphate isolated from cells in pus
- called it NUCLEIN (known as DNA)
Location- EUKARYOTES- in nucleus
- DNA is packaged with proteins forming CHROMATIN
- Genomic DNA of eukaryotes is divided into linear CHROMOSOMES
- PROKARYOTES- not membrane bound
- Generally circular, supercoiled DNA- NAKED
,Eukaryotes/ Prokaryotes
Prokaryotes
Small and simple- little internal structure
Up to 2µm in diameter- 1000 times shorter than extended length of its genomic DNA
Bacteria, blue-green algae- Cynobacteria
Prokaryotic chromosomes can range in size from 0.6 million base pairs to 10 Mbp (megabase pairs)
Eukaryotes
Cellular components of plants, animals, fungi, algae
Distinct nucleus containing DNA- separated by distinct membrane
Internal structures- Membrane- bound organelles (Mitochondria, Vesicles)
About 20µm
Chromosomes
Named because some structures could be visualised using special dyes- seen by staining dyes that pick out AT or GC -
rich regions of genome (condensed VS less condensed)- Produce pattern of bands- UNIQUE to each chromosome
Cells of given species contain constant number of chromosomes- e.g. humans have 46 chromosomes
- This number doubles immediately before CELL DIVISION- MITOSIS
Half the number of chromosomes seen in gametes
- Normal cell- DIPLOID
- Gametes- HAPLOID
Each chromosome is SINGLE DNA MOLECULE- associated with PROTEINS, folded into COMPACT STRUCTURE
All cells (except few specialist cells) contain TWO COPIES of each chromosome – pair are called
HOMOLOGOUS Chromosomes
Full set of chromosomes- KARYOTYPE
During cell division….
Cell Division requires production of complete copy of
DNA contained within cell
- results daughter cells with each contain
complete copy of genomic DNA
Genome
DNA condensation is mediated by histone proteins- results in formation of chromatin- DNA that has
condensed using protein-DNA complexes
During interphase- chromosomes are less condensed than in mitosis. Mitotic chromosomes are more easily
visualised in cell- they are tightly compacted
Mitotic chromosomes must be tightly compacted to ensure proper segregation of DNA during cell division
, Although genomic DNA must be condensed to fit within cell- must also be
arranged in specific regions can be exposed to allow enzymes and other
proteins to bind and initiate DNA replication and transcription
Less condensed, gene rich chromatin- Euchromatin- offers more sites for
protein binding than heterochromatin- more condensed regions
Majority of heterochromatin doesn’t contain genes- some region s play important
role in chromosomal division and maintenance
Centromere- region of connection between sister chromatids is composed of
heterochromatin
Sister chromatids- two identical copies of replicated DNA contained in mitotic chromosome- remain attached at
centromere
Telomere- region of heterochromatin found at ends of chromosomes
- function to maintain length of chromosomes after replication
- composed of short, repetitive DNA sequences with high G content- G-rich structures are able to form loops that
helps protects the ends of chromosomes from degradation
G-rich regions can form G-quadruplex structures
Genes
Genes- Units of Genetic Information
Basic organisation of gene divided into two components- promoter and coding sequence
Promoter- specific DNA sequence that occurs upstream 5’ of coding sequence
- necessary for interactions with transcription factors- proteins that recognise specific DNA
sequences and facilitate transcriptional initiation at gene promoters by recruiting RNA polymerase
Prokaryotic genes can either be monocistronic or polycistronic
- Monocistronic gene- promoter is followed by single protein- coding sequence -encode one protein
product in single RNA transcript
- Polycistronic gene- promoter is followed by multiple coding regions
- transcribed into single mRNA, but translation of this mRNA results in production
of three different proteins- one from each coding region
Short regions of DNA between coding regions of polycistronic genes contain instructions to halt translation
between each- allows proteins to be produced as separate units
Polycistronic genes that contain coding sequence for proteins involved in single biochemical process/ pathway-
operons
Many genes in eukaryotes contain coding regions- exons, may be separated by non-coding regions- introns
From left, first region indicated encodes upstream regulatory sequences- transcriptional regulatory proteins bind.
These upstream regulatory sequences can be located hundreds/ thousands of base pairs upstream/downstream of
activated promoter- they must be located on same chromosome as promoter
Promoter region is separated from coding sequence by region knows as 5’ Untranslated region (5’UTR)- Region
isn’t translated but rather contains sequences that when transcribed into RNA will facilitate interaction with protein
translational machinery.
At the other end of coding sequence is another untranslated region – 3’ untranslated region (3’UTR)- region
contains sequences necessary for termination of transcription by RNA polymerase
After primary RNA transcript has been synthesised, initial processing of RNA occurs- Includes:
addition of covalent nucleotide modification at 5’terminus of mRNA- 5’cap
polyadenylation (addition of adenine-containing nucleotides) at 3’end- 3’poly(A) tail
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