Biology 311 Human Genetics
Fall 2004
Lecture 1: Review of Molecular Biology: Eukaryotic Gene Expression
Reading: Chap. 1, Strachan and Read (2004) Human Molecular Genetics,
third edition.
Outline:
1. Review of molecular biology: Study questions
2. Overview of gene expression
3. Eukaryotic gene structure
4. Regulation of transcription
5. RNA processing
Lecture:
1. Review of molecular biology
 Review most topics by reading Chapter 1 and completing the study
questions, due next Wed. in class.
 Today we will focus on eukaryotic gene structure and expression, topics
that may be less familiar to you.
 No class on Friday, as Dr. Bachman will be away Thursday-Sunday; see
Dr. Lentz for questions.
2. Overview of gene expression
DNARNAprotein
Nucleic acids:
Proteins:
DNA and RNA, encode information
carry out many cell functions
Processes:
Replication (DNA DNA)
Transcription (DNA RNA)
Translation (RNA protein)
3. Structure of eukaryotic genes
5'
exon 1
intron
exon 2
promoter
3'
poly(A) sites
Terms:
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Exon
Intron
5’ end
3’ end
upstream
downstream
promoter
transcription start site
poly(A) addition sites
4. Regulation of transcription
Control at the level of RNA synthesis requires
 Promoters
 Transcription factors
 RNA polymerase
Different RNA polymerases for each type of eukaryotic gene
features of promoter:
 made of many short sequence blocks
 serve as binding sites for proteins that activate transcription= "transcription
factors"
 regulatory elements act in cis=on same DNA strand
 regulatory proteins bind to these sites; attract RNA polymerase to the
gene to stimulate transcription
 can have ubiquitous and tissue-specific transcription factors
 enhancers=sequence elements that promote gene transcription, can be
located far away from beginning of gene
 silencers=sequence elements that suppress transcription, can also work at
a distance
examples of promoter elements see Table 1.5
Element
GC box or Sp1
site
TATA box
CAAT box
Sequence
GGGCGG
location
Bind factor
proximal promoter Sp1
TATAAA
CCAAT
-25
-80
CRE
GTGACGT(A/C)A(A/G)
Promoter or
enhancer
2
TFIID
C/EBP,
CTF/NF-1
CREB/ATF
family
5. RNA processing
Most eukaryotic transcripts are processed. For mRNAs:
 Remove introns (sequences that don't code for proteins)=RNA splicing
 Add cap to 5' end--a modified nucleotide (7-methylguanosine
triphosphate)
 Add poly(A) tail to 3' end=stretch of 200 As.
a. Removal of introns
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introns contain non-coding sequences and must be removed (see Fig.
1.14).
GT-AG rule (or GU-AG rule) refers to conserved nucleotides in the intron
at the intron-exon junction.
There is also a conserved site close to the 3' end of the intron (~40 bp
away) called the branch site (see Fig. 1.16).
RNA processing to remove introns is carried out by a large structure called
the spliceosome.
Spliceosome is made of small nuclear RNAs (snRNAs) and many
proteins.
b. Capping
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add nucleotide to 5' end of mRNA
purpose:
o protect mRNA from degradation 5'3'
o help transport from nucleus to the cytoplasm
o important for RNA splicing
o important for attachment of mRNA to small subunit of ribosome in
translation
c. Polyadenylation
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signals for terminating transcription not really known
sequence AAUAAA near 3' end of primary transcript made by RNA
polymerase II signals cleavage
after cleavage, polyA polymerase adds about 200A residues to 3' end.
Possible functions:
o Aid transport of mRNAs to cytoplasm
o Stabilize mRNA to prevent degradation
o Facilitate translation
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