Molecular genetics
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What does DNA consist of?
DNA is a polynucleotide Each nucleotide consists of: -a nitrogen base (adenine, guanine, cytosine, or thymine) -a pentose sugar (deoxyribose) -a phosphate
What does 5 prime and 3 prime mean
5 prime: the 5th carbon of each sugar has a phosphate group attached 3 prime: the 3rd carbon of each sugar has a hydroxyl group attached
What are the difference between DNA and RNA
-DNA- sugar: deoxyribose bases: GCAT length and shape: double-stranded, long location: nucleus -RNA- sugar: ribose bases: GCAU (uracil) length and shape: single-stranded, short location: nucleus, cytoplasm
What are genes?
coding regions on DNA –> determines phenotypical characteristics of an organism
What is a mutation? How is it caused?
an alteration in the DNA sequence –> may be caused by chemical agents, ultraviolet radiation, or natural causes, can also occur during the process of DNA replication e.g. dyes, tobacco smoke, UV rays, X rays, benzene, viruses (ex. HPV)
What are telomeres?
-are repetitive sequences of DNA at the ends of chromosomes -prevent the loss of genetic information during DNA replication
What are the three steps of DNA replication?
Initiation, elongation, termination
What is Initiation? And what enzymes are involved with it?
a step in DNA replication -separating the two strands -creates a replication bubble with two replication forks Enzymes Involved: DNA Gyrase, DNA helicase, ssB’s
What is DNA gyrase? and what step is it in?
In step 1, Initiation -helps unwind the DNA by relieving the tension in the double helix
What is DNA helicase? and what step is it in?
In step 1, Initiation -unwinds DNA by breaking the H-bonds between the strands
What are ssB’s, and what step are they in?
In step 1, Initiation -single-stranded binding proteins keep strands from re-annealing (re-binding)
What is RNA primase? and what step is it in?
In step 2, Elongation -anneals the RNA-primer to the exposed 3’ end of the replication fork
what is RNA primer? and what step is it in?
In step 2, Elongation -10-60 base strand of RNA that serves as a starting point for DNA synthesis
What is DNA polymerase III? and what step is it in?
In step 2, Elongation -Adds complementary bases in the 5’ to 3’ direction -the energy released by removing 2 phosphate groups allows the bonding -the strand that is copied continuously (5’ to 3’) towards the replication fork is called the leading strand
What is elongation?
the second step of DNA replication -building complementary strands
What are the differences between the leading and lagging strand?
-Leading strand is being replicated towards the fork, and the lagging strand is being replicated away from the fork -Leading strand is being replicated continuously, while lagging strand is being replicated in discontinuous fragments
What are Okazaki fragments? and what step are they in?
In step 2, Elongation -DNA polymerase III only moves 5’ to 3’ so the lagging strand is built discontinuously (in short segments) –> that is what okazaki fragments are!
What is DNA polymerase I? and what step is it in?
In step 2, elongation -removes the RNA primers and replaces the primers with appropriate DNA bases
What is DNA ligase? and what step is it in?
In step 2, elongation -attaches Okazaki fragments by creating phosphodiester bonds between sugars and phosphates
What is Termination? And what is involved in it?
the third and last step of DNA replication -completion of process DNA polymerase II
What is DNA polymerase II, and what step is it in?
In step 3, Termination -proofreads the newly synthesized DNA and fixes incorrect nucleotides -after proofreading, termination occurs when the two new DNA molecules separate from each other
What are the steps in making mRNA?
Initiation, Elongation, Termination, Post-transcriptional modifications
What is involved in Initiation (mRNA)?
-RNA polymerase binds to a specific region of the DNA, upstream of the gene to be transcribed (called the promoter) -The DNA is unwound and the two strands are separated
What is involved in Elongation (mRNA)?
-only 3’ to 5’ strand is copied (called the template strand) -the unused strand (5’ to 3’) is called the coding strand -free floating nucleotides are H-bonded to their complementary bases by RNA polymerase (2 phosphates are removed to create a bond) -RNA polymerase moves along the DNA (in the 5’ to 3’ direction), unwinding and separating as it goes while the DNA winds back up behind it -the mRNA hands free of the side of the DNA strand attached only at a few base pairs