Chapter 2.B-Molecular Biology Flashcards
How many carbon sugar is in a nucleotide?
5 carbons
Which part of the nucleotide makes it charges, and whats the charge?
Phosphate (-) charged
How to 2 nucleotides link together?
Covalent bonds formed betw. phosphate of one nucleotide and the pentose sugar of the next.
Creates a strong backbone
Different between DNA and RNA (3)
1. DNA = DEOxyribonucleic acid RNA = Ribonucleic acid 2. Polymers: \+ DNA = 2 polymers of nucleotide (double stranded) \+ RNA = 1 polymer of nuceotide (single stranded) 3. BASES: \+ DNA = ATCG \+ RNA = AUCG
Which C can the phosphate of another nucleotide linked to?
3rd Carbon of the 3’ (prime) terminal
Which part of the nucleotide can the pentose of another nucleotide linked to?
The phosphate of the 5’ terminal
What did Watson and Crick discover?
The structure of the DNA through model-making
What did Rosalind Franklin discover?
Photograph ‘51’ (Double Helix of DNA)
What did Hershey and Chase’s experiment show?
Evidence that DNA is hereditary genetic material.
What is the process of Hershey and Chase’s experiment?
T-2 Phage virus used
1. PROTEIN COAT of the 1st group of viruses radioactively labelled in RED with radioactive SULFUR
2. DNA of the 2nd group of viruses radioactively labelled in BLUE with radioactive PHOSPHORUS.
3. The viruses left to infect e.coli bacterial cells
4. When the bacteria and viruses were separated
+ RED (PROTEIN COAT) molecule on the outside of the bacteria
+ BLUE (DNA) molecule on the inside of the bacteria
What type of replication happens in DNA?
Semi-conservative
What did Meselson and Stahl’s experiment show?
Evidence for Semi-Conservative replication
What did Meselson and Stahl use in their experiment?
N-15 rare isotope of Nitrogen. = denser than normal one
Steps of the Meselson and Stahl experiment.
- Cultured bacterium E.coli for 14 generations in a medium with ONLY N-15
- Transferred bacteria abruptly to a medium in which all N was N-14
+ The bacteria divided and replicated DNA every 50 mins - Collected samples of DNA from bacterial culture for several hrs from time when it was transferred to N-14 medium
- Extracted the DNA and measured its density by ‘Caesium Chloride density centrifugation’
What does DNA gyrase do in DNA replication?
Relieves the strain on the DNA
What does Helicase do in DNA replication?
Separates the 2 strands by breaking the H. bonds between bases
What is Helicase made of?
+ 6 globular polypepetides arranged in donut shape
+ Polypeptide = put together with 1 strand of DNA molecule passing through the centre (of donut) and the other = outside it.
Where does Helicase get the energy to break the H. bonds?
ATP
What is the function of DNA polymerase in DNA replication?
Links nucleotides together to form a new strand, using the preexisting strand as a template.
Which end of the carbon does the DNA polymerase add on to the existing strand?
+ Adds he 5’ of the FREE NUCLEOTIDE
= to the 3’ of the EXISTING STRAND
By forming covalent bonds!
DNA Sequencing steps (5)
1) The DNA sample is replicated by PCR
2) Many of the unknown DNA that’s to be seq. = placed in test tubes
3) Primers and some free nucleotides = added so that DNA can be replicated
4) Dideoxyribonucleic acid (dideoxyribonucleotides) = labelled with fluorescent markers added to matching labelled test tubes (A,T,C,G)
5) The DNA continues to replicate until it comes to a ‘dodgy’ base = randomly attaches to it’s complementary base = is when replication of that strand stops.
Transcription
The synthesis of mRNA copied from the DNA base sequence by RNA polymerase.
Steps of Transcription (5)
1) RNA polymerase binds to the site on the DNA at the start of the gene
2) RNA polymerase moves along the gene separating the DNA into single strands
→ pairing up the nucleotides with its complementary bases on 1 strand of the DNA
→ No Thymine in RNA so its URACIL instead
3) RNA polymerase forms covalent bonds betw/ the RNA nucleotides
4) RNA separates from the DNA and the double helix reforms
5) Once the Transcription stops at the end of the gene = the completed RNA is released
Sense strand
Has the same base sequence as the RNA produced
Antisense strand
The template strand
→ has complementary base sequence to the RNA and sense strand
Post Transcriptional Modification (PTM)
When Eukaryotic cells modify mRNA after the transcription of the DNA
At which pts can regulation of gene expression occur in prokaryotes and eukaryotes?
Transcription, Translation, Post-TranSLation regulation
Why don’t prokaryotes undergo PTM?
Cuz they don’t have a membrane surrounding their genetic material so once a SINGLE codon is transcribed it can immediately be tranlated
What does the separation of location of transcription and translation allow to happen?
Significant Post-TranSCriptional modifications
→ e.g removing introns (prokaryotes don’t have introns)
What does splicing of mRNA do?
Increase the number of diff. proteins an organism can produce.
Alternative Splicing
+ Process during gene expression where a single gene codes for multiple proteins
When does alternative splicing occur
In genes that have multiple exons
→ apart of the exon may or may not be included in the final mRNA
What does the proteins translated from alternatively spliced mRNAs differ in?
Amino acid sequence AND Biological funct.
Sequence of occurrence of PTM
DNA → pre-mRNA → splicing → mature RNA
Eukaryotic DNA is regulated in response to what?
Variations in environmental conditions
The 2 introns (promoter proximal elements) that regulate transcription
+ Enhancers = increases the rate of transcription when proteins binds to them
+ Silencers = decreases the rate of transcription when proteins binds to them
Promoter proximal elements
Nearer to the promoter and binding of proteins to them = necessary to initiate transcription
The impact of environment on gene-expression (2)
+ Changes in external/internal environment results in changes in gene expression
+ Chemical signals with cells leads to changes in levels of regulatory proteins or transcription factors
→ Therefore change in gene expression as response t intra/extra cellular conditions
Chemical modifications of which part of the histone protein determines whether or not a gene is expressed ?
The tails
Typically what charge do histones have?
+ Positive charge due to the lysine residue
→ associate tightly w/ negatively charged DNA to form condensed structures that INHIBIT transcription
Histone Acetylation causes?
Neutralises the charge on = DNA is less tightly coiled
→ INCREASES transcription
Types of Chromatin (2)
1) Heterochromatin = when DNA = supercoiled and is not accessible for transcription = exists as condensed form
2) Euchromatin = when DNA is loosely packed = accessible to transcription
Promoter
The part of the DNA to which RNA polymerase binds to, to initiate the transcription of DNA
Terminator
Initiates the end of the DNA strand that is transcribed
DNA methylation
When a methyl group is added to CYTOSINE
Why is DNA methylation dangerous?
It is permanent and lasts a long time
In genes that are methylated what happens to the cytosine?
It gets shut down
→ The DNA that is methylated is NOT expressed
What are the levels of DNA methylation of the genome or of specific genes associated w/? (5)
\+ Age \+ Diet \+ Environmental factors \+ Emotions during important developmental stages \+ Exposure to infectious diseases
Smoking increases methylation
Therefore some genes are not transcribed and if they are involved in the control of the cell cycle = tumour is formed
Methylation increases w/?
Age
→ occurs as a result of environment
→ can be inherited by offspring
Transcription factors
Protein that controls the rate of transcription of genetics info from DNA
RNA can only bind when?
There are transcription factors present
Activator
Regulatory protein that binds to enhancers to increase rate of transcription
Repressor
Regulatory protein that binds to silencers to decreases transcription
Degegnerate
When multiple codons can code for the same aa’s
tRNA
single strand of RNA folded on top of itself
Codon
The 3 base seq. on the mRNA
Anticodon
The complementary 3 base seq. on the tRNA
Porcine and Bovine insulin extracted from what animals?
Pigs and cattles
Human insulin first available was made from?
GM E.coli bacteria
What organisms have been GMed to produce insulin?
+ Yeast
+ Safflower
+ E.coli
Why does GM work on other organisms to produce human insulin?
Because they all share the same genetic code
→ the tRNA w/ a particular codon having the same aa attached to it as with humans
tRNA molecules have? (3)
+ Section that becomes double stranded by base pairing = creating loops
+ A triplet of bases = ANTIcodon = part of a loop of 7 unpaired bases
+ Base seq. CCA at the 3’ end which forms a site for attaching aa
