nucleic acids
Draw a nucleotide and circle/label the 3 different components
Pentose sugar, phosphate group, nitrogenous base
What is the central dogma? (Definition)
What are the 2 processes of gene expression?
The central dogma describes the flow of information in cells
DNA -> mRNA (transcription)
mRNA -> polypeptide (translation)
What are the 2 processes involved in gene expression? What happens in each?
Transcription (info in DNA is copied to make mRNA)
Translation (mRNA is used to synthesize a polypeptide)
What is the function of sigma factor in transcription?
What is the purpose of the hairpin loop in transcription?
*What steps of transcription are each seen in?
Sigma factor must bind to RNA polymerase for the process to happen
The hairpin loop forms during the termination phase and is a signal for everything to dissociate
Draw a molecule of tRNA. Label the 3' and 5' ends and the anticodon loop
What is the importance of the 3' end?
3' end: amino acid binding site
What are the key differences between DNA and RNA?
(Mention the pentose sugar in each, the structure of both, stability)
DNA: double stranded, has deoxyribose as the sugar, is more stable, contains genetic info
RNA: single stranded, has ribose as the sugar, different structures/functions, can transmit genetic info
What type of bond forms between nitrogenous bases? How many form between A & T? C & G?
Hydrogen bond
2 between A&T, 3 between C&G
What is a gene?
A sequence of nucleotides in DNA that code for a protein
*The protein that is synthesized can lead to the expression of certain traits (eye color, etc)
What are the 2 strands of DNA called in transcription? Which one is used to synthesize mRNA?
Template/non-coding strand- used to make mRNA
Non-template/coding strand
In translation, how does a new peptide bond form between the polypeptide chain in the P site and the new amino acid in the A site?
C end of polypeptide is released from tRNA at P site and is joined to the free N group of the amino acid in the A site
What are the different nitrogenous bases? Where are they found, and are they purines or pyrimidines?
Purines: adenine, guanine
Pyrimidines: thymine (DNA only), cytosine, uracil (RNA only)
Draw a strand of nucleotides, label the 3' and 5' ends
3' end: open -OH group on pentose sugar
5' end: open phosphate group
Draw a 'gene' and label the different regions on the gene that are important in transcription. What is the function of each?
-Promoter region: signals the beginning of transcription
-Transcribed region: specifies an amino acid sequence
-Terminator region: signals end of transcription
In eukaryotes, what process happens after transcription and before translation? What is involved in this process?
Why doesn't this process happen in prokaryotes?
RNA modification/processing
Introns are removed
5' guanine cap added
3' poly-A tail added
What are the 3 characteristics of the genetic code?
Give examples of each
What is the 'wobble position'?
1) Unambiguous: a single codon never codes for more than one amino acid
2) Conservative: the first 2 bases in codons code for the same amino acid (almost always)
3) Redundant: more than 1 codon specifies 1 amino acid
Wobble position: the 3rd position of the anticodon may not be complementary to the 3rd base in the codon
If a molecule of DNA contains 30% Thymine, what percentage would be Guanine?
20%
(30% thymine=30% adenine=60%
40%/2= 20% guanine, 20% cytosine)
Draw two nucleotides being joined together. What type of bond connects them and where?
Phosphodiester bond between 3' and 5'. New nucleotides are always added to the 3' end!
Explain the structure of a ribosome.
What is it made of and what are the 2 subunits? What are the functions of these subunits?
rRNA and proteins (where is rRNA made?)
Small subunit: interacts with the tRNA anticodon, which matches with the mRNA codon
Large subunit: catalyzes the formation of peptide bonds
Given this sequence of nucleotides of the coding strand of mRNA, give the mRNA sequence
5' ACG GGC TAA TTG 3'
Non-coding/template strand:
5' TGC CCG ATT AAC 3'
mRNA: 5' ACG GGC UAA UUG 3'
Explain the 3 sites of the large ribosome and what happens in each
E site: exit site, uncharged tRNA leaves ribosome
P site: (peptidyl) tRNA holding growing polypeptide chain passes polypeptide to the tRNA in the A site
A site: (aminoacyl) New, charged tRNA enters ribosome
What are the levels of complexity of RNA?
nucleotide, single strand, hairpin loop (secondary structure), tertiary structure
What are the levels of complexity of DNA?
Nucleotide, single strand, double helix, chromosome, genome
Given this sequence of DNA (non-coding strand), give the mRNA, anticodon, and amino acid sequence
5' ACG TTA CCG GAA 3'
mRNA:
anticodon sequence:
polypeptide:
mRNA: 5' UGC AAU GGC CUU 3' (codons)
Anticodon: 5' ACG UUA CCG GAA 3' (tRNA anticodons)
AA: Cys-Ile-Gly-Leu
*Remember to read 5' to 3'
Describe, in detail, the 3 steps of transcription
1. initiation- sigma factor binds to RNA polymerase and brings RNA poly to the promoter region of the gene. RNA polymerase unwinds the double helix to form a replication bubble
2. elongation: RNA polymerase synthesizes mRNA in the 5' to direction
3. termination: RNA poly reads the terminator region. As a result, a hairpin loop forms in mRNA and the process ends.
Describe in detail, the 3 steps of translation
*How is the order of initiation different in prokaryotes vs eukaryotes?
1. Initiation
(prokaryotes) mRNA binds to small ribosomal subunit
initiator tRNA binds to the start codon (AUG) in P site
large ribosomal subunit binds to small subunit
2. Elongation: charged tRNA enters A site, peptide bond forms, translocation of ribosome
3. Termination: stop codon is reached, release factor binds to stop codon in A site