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Genes and chromosome - Coggle Diagram
Genes and chromosome
Central dogma
once information has got into a protein it can't get out
DNA replication
Eukaryotic chromosomes are in this state after replication
at metaphase during mitosis
transcription
DNA molecule template
mRNA( Three nucleotides code for one “codon.”)
tRNA binds
translation
Protein sequence determines its biological function
DNA Supercoiling
Linking Number (Lk)
(+): right-handed helix
Lk = Tw + Wr
Twist (Tw) is the # twists or turns of the helix
Writhe (Wr) is the # coils
Superhelical Density=specific linking difference
characters
with the help of proteins to
prevent strands from rotating
separation of the strands easier
double-stranded DNA helix.
most Cellular DNA Is Underwound(less relaxed)
influence transcription and
replication
Topoisomer
same bp
same sequence
different degree of
supercoiling
others
Conversion between topoisomers requires a DNA
strand break.
negatively supercoiled DNA (more compact)
travels faster in an agarose gel electrophoresis
Topoisomerases
what:Enzymes
That Change Lk
– Type I:cut in one DNA strand
Type II:cut in both DNA strands
E. Coli
Topo I and III (Type I)
increase Lk
single-stranded breaks
Topo II (DNA gyrase)
decreases Lk
uses ATP and double-stranded breaks
Topoisomerases Are Targets for Antibiotics
Topoisomerase Inhibitors Used as
Chemotherapy Agents
forms:
Plectonemic
seen in plasmids
Toroid/solenoid
in chromatin
bacteria and virus
Many Viral Genomes Are RNA
Many viruses are surrounded by
protein coat
HIV
phage Q(嗜菌體)
Bacterial Genomes Are Double-Stranded Circles
double-stranded
circular plasmids
no essential genes
plasmid exchange
Some Bacterial Genomes Also
Contain Introns
do not interrupt protein-coding
sequences
interrupt mainly tRNA sequences
introns encode catalytic RNA sequences(insert and reverse transcribe themselves into the genomic
DNA)
human
only a small fraction (1.5%) of the total genome
encodes for proteins.
exons
translated into
amino acid sequence
1.5%
exon
mRNA sequences are spliced together
introns
are transcribed but
not translated
removed after transcription
interrupt mainly tRNA sequences.
transposons
what: Sequences That Can
Move Within the Genome
within the genome of a single cell
account for ~50% of the human genome
Eukaryotes Also Contain Highly Repetitive
DNA or Simple Sequence Repeats (SSRs)
Also known as “satellite” DNA
centromeres(著絲點)
Centromere Sequences Are Where
Proteins Attach
during mitosis
Have AT-rich repeated sequences
telomeres(端粒)
Telomere Sequences Cap the Ends
of Eukaryotic Chromosomes
keep DNA ends
from unraveling
added by enzyme telomerase (protein+nucleotides)
Cellular Aging
telomeres are shortened after each
round of replication
越來越短，越來越老
Underwinding Facilitates Additional
DNA Structural Changes
Helps to maintain structure of cruciforms at palindromes(回文)
Cruciforms rarely occur in relaxed DNA
cruciform 穩定結構
chromatin
consist of
fibers of protein
DNA
small amount of RNA
histones
nucleosomes.
Mitochondria and Chloroplasts Also Have DNA
Double-stranded circles
mitochondrial DNA
It codes for
mitochondrial rRNA
mitochondrial tRNA
mitochondrial specific protein
most encode by nuclear gene
Eukaryote DNA Is in Multiple
Discrete Chromosomes
