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BIOC0005 Molecular Biology All Lectures Flashcards PDF - First 1/2
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🧬BIOC0005 II - Molecular Biology
Nuclear Genome: Gene Families,
Pseudogenes and Repetitive DNA
outline composition of 3 genomes found in each somatic cell?
a) genome inherited from mother —> 22 autosomes + 1 sex chrom = 23 chrom ~3 x
10^9 bp
b) genome inherited from father —> 22 autosomes + 1 sex chrom= 23 chrom ~3 x
10^9 bp
c) mitochondrial genome —> non-nuclear
#so total nuclear genome ~6 x 10^9bp per cell
#chromosomes range in size from 50-260 Mbp DNA
tiny 1.5% of human genome codes for _______, decent 25% codes for _______,
but majority 43% codes for ______?
1.5% —> protein-coding regions i.e exons
25% —> introns
43% —> non-functional repetitive DNA
#other DNA includes regulatory regions of genes, pseudogenes, fragments of
genes
when is mRNA considered "processed mRNA"?
after splicing and poly adenylation
#exon Exits nucleus, introns spliced out so stay In nucleus
describe role of 5' and 3' flanking sequences surrounding protein-coding genes?
5' control region —> promoter to bind RNA pol II + enhancer to increase transcri by
RNA pol II
BIOC0005 II - Molecular Biology 1
, 3' control region —> some genes have enhancers here too
#RNA pol II is eu that transcribes protein coding genes
describe difference between promoter and enhancer seq?
eu RNA pol II can't bind to promoter by itself so needs help of additional complex to
form complex to allow correct positioning onto promoter...
promoter = DNA seq where RNA pol II will ultimately bind
enhancer = DNA seq where additional proteins bind to form complex that increases
affinity for RNA pol II to promoter
what does list of examples above show about trend in size of gene and % of DNA in
the gene that codes for protein?
regions of exons can differ substantially even within genes of similar size
a lot of the genome is taken up by introns rather than exons
how are gene families thought to have arisen?
gene duplication = duplicated genes with some base changes = gene products
encode similar proteins but with different properties
#suggested due to their Seq similarity
define gene cluster?
multiple genes related in seq i.e found on same stretch of DNA
BIOC0005 II - Molecular Biology 2
, describe organisation of functional genes within human alpha and beta globin gene
families above?
genes arranged in order they are transcribed throughout development...
a globin gene family —> zeta transcribed only in embryo, replaced by alpha in
foetus and adult
b globin gene family —> epsilon transcribed only in embryo, replaced by gamma
transcription in foetus, replaced by delta and beta transcription in adult
#psi are pseudogenes
#theta refers to DNA seq producing mRNA detected in embryonic tissue but no
protein
#functional genes on each cluster are similar seq but accquired at diff. stages of
development
explain importance of changes in transcription throughout development?
gene cluster proteins within same gene family are similar but have diff. properties =
diff. ones essential for diff. stages of development
e.g gamma Hb chain much higher affinity for O2 than adult mother b Hb chain
#note also the location of transcription changes e.g beta globin chain transcribed a
bit in foetus but don't get sufficient transcription including bone marrow cells until
after birth
describe role of histone gene family, including specific roles of: H1, H2A, H2B, H3,
H4?
BIOC0005 II - Molecular Biology 3
, histone gene family —> nucleosome formation for DNA packing
H1 —> pulls different nucleosomes together to further condense DNA
H2A, H2B, H3, H4 —> two of each come together to form nucleosome octamer
#~140bp DNA wraps twice around histone octamer
humans have 60 histone genes grouped into ____ gene clusters, distributed over
____ chromosomes?
60 genes —> 11 gene clusters —> 7 chromosomes
state 2 features of histone genes that allows them to be expressed very quickly for
immediate use following DNA replication?
a) histone genes don't have introns —> no time wasted splicing
b) histone mRNA not poly adenylated —> quickly start translation
unlike the globin gene family, each member within a particular histone gene family
that arose from duplication encodes _______ protein?
identical
#shows crucial to function as enormous selective pressure to maintain these genes
and proteins
#for Hb this means proteins with different important properties, for histones this
means increased production of identical product
explain 3 outcomes of gene duplication depending on selective pressure of
duplicated gene?
a) selective pressure on both genes —> both genes persist and have either very
similar (globin) or identical (histone) protein products
BIOC0005 II - Molecular Biology 4
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