Unit 2: Lecture 3 Flashcards
How many protein coding genes does the human genome contain?
20, 000
In molecular biology, what is a gene called?
transcription unit (ie. the sequence of DNA that produces a RNA transcript
What does a sequence of nucleotides in DNA code for?
a single RNA molecule, along with the sequences necessary for its transcription
What does a sequence of nucleotides in DNA usually contain?
promoter
RNA-coding sequence
terminator
What is mRNA?
messenger RNA
- transcribed from DNA
- encodes protein (translated into a polypeptide chain in protein synthesis)
- considered “unstable” RNA
What is RNase?
enzyme that degrades RNA, and are present everywhere
What is the half-life of mRNA (when 50% of RNA is degraded)?
minutes for bacteria, hours for eukarya
What do genes code for?
genes are templates for RNA synthesis
What are the 3 types of RNA made from a gene?
mRNA (messenger RNA)
tRNA (transfer RNA)
rRNA (ribosomal RNA)
Which type of RNA is the only RNA that encodes a protein?
mRNA
What does tRNA do?
- considered as “stable” RNA
- folds to form 2° structures
- carries amino acids for translation
What does rRNA do?
- considered as “stable” RNA
- complexes with proteins to make a ribosome
What is a ribosome?
rRNA + protein
What protects RNA from degradation?
the functions of tRNA and rRNA
What sequences do genes have?
promoters and terminators
What is a promoter?
- DNA sequence where regulatory proteins called transcription factors bind to recruit the RNA polymerase to start transcription of one DNA strand
- controls gene expression
What do terminators do?
tell RNA polymerase where to stop transcribing
How is a gene ‘read’?
from promoter sequence to terminator sequence
ie. the protein that transcribes (RNA polymerase) reads the gene starting around the promoter and moves along to the terminator
What are transcription factors?
DNA binding proteins
What do DNA binding proteins do?
- could bind in either major or minor grooves of DNA
- recognize specific sequences of base pairs, therefore R groups interacting with molecular groups on a GC base pair will be different than a AT base pair
- bind by H-bonds and other non-covalent interactions (ie. amino acid side chains (R groups) interact with the bases)
What does how strongly a protein binds determine?
how long it will stay on the DNA strand and whether transcription will proceed
What is transcription regulated by?
- how often RNA POL (with Sigma and/or other transcription factors) binds to the promoter
- how tightly transcription factors bind to the promoter
What results in more RNA transcripts made from a particular gene?
binding more often and tightly
How does the sequence of a promoter control gene expression?
different promoters can have different sequences but still can be recognized by transcription factors
What are consensus sequences?
- calculated order of most frequent nucleotides (bases) found at each position in a sequence
- model for a DNA binding site
- conserved DNA sequences, they bind to transcription factors in promoters
Do promoters from different genes have different DNA sequences?
yes, they can have similarities too
What is a strong promoter?
promoters that are closer to consensus sequence will bind to transcription factors (and therefore RNA POL) MORE tightly (strongly) and MORE often
What is a weak promoter?
promoters that are closer to consensus sequence will bind to transcription factors (and therefore RNA POL) LESS tightly (weakly) and LESS often
What are weak vs. strong interactions?
non-covalent interactions between R groups on the protein and bases on the DNA
DNA is transcribed to mRNA, which will be translated into a
protein. The sequence of the mRNA will include…
the complementary RNA sequence to the DNA starting with the transcription start site
What is the template strand in DNA?
strand from 3’ to 5’
- base pairs are complementary to the template strand
- the opposite, non-template strand is anti-parallel to the template strand and is complementary to the template
- mRNA is complementary to the DNA template
Why is the non-template strand sometimes called the ‘coding’ strand?
it resembles the mRNA that encodes the protein
What are the upstream and downstream directions relative to?
promoter
polymerase reads genes in the 3’ to 5’ (promoter to terminator) direction on the template strand
What is the upstream of the promoter direction?
towards 3’ end
What is the downstream of the promoter direction?
towards 5’ end
Where is the promoter found?
upstream of the terminator
Where is the terminator found?
downstream of the promoter
In genes encoding mRNA, what doe the coding sequence or coding region specify?
the amino acids of the protein
What are the differences in bacterial and eukaryotic transcription/translation?
bacterial: same space and time
eukaryotic: DNA is enclosed in nucleus, transcription occurs in nucleus, translation occurs in cytoplasm
