Molecular Genetics Flashcards
I can identify the components of ribonucleotides and deoxyribonucleotides (i.e. sugar, phosphate, nitrogen containing base) and draw a simple diagram to illustrate their structure.
DNA contains a H group on the second carbon. It has four different nitrogenous bases, Adenine, Thymine, Cystine, and Guaine.
RNA has an OH group on the second carbon. It has four different nitrogenous bases, Adenine, Uracil, Cystine, and Guaine.
I can identify similarities and differences between deoxyribonucleic acid and ribonucleic acid.
DNA has two strands, deoxyribonucleotides, the base pairings are A&T and C&G, replicates and stores genetic information, and is found in the nucleus.
RNA has one strand, ribonucleotides, converts genetic information contained in DNA to build proteins, and is formed in the nucleus and moves to the cystoplam.
I can identify that the ‘rails of the twisted ladder’ are held together by covalent bonds while the ‘rungs of the twisted ladder’ are held together by hydrogen bonds.
The sides or rails of the ladder are made up of deoxyribose sugars and phosphate groups held together by covalent bonds. The rungs of the ladder are held together by hydrogen bonds that form between the nitrogenous bases.
The carbon group on the fourth carbon connects to the phosphate’s oxygen. The oxygen across from it then connects to the 3 third carbon.
I can identify base pairing relationships within DNA and when DNA is used to produce mRNA.
Apple in the three.
Car in the garage.
DNA is turned into mRNA during transcription. Transcription in the DNA-directed synthesis of mRNA by an enzyme complex that includes RNA polymerase. Like DNA, RNA is a polynucleotide, which carries genetic information. There are few differences between DNA and RNA. RNA is single stranded and DNA is double stranded. RNA is short, it only contains one gene. RNA uses ribose sugar and DNA deoxyribose in the construction of nucleotides. RNA contains uracil rather than thymine. It’s purpose is to bring information for new proteins.
mRNA or messenger RNA’s job is to carry information from the nucleus to the cytoplasm.
I can explain why the two strands of the DNA double helix are antiparallel.
The leading strand runs in the 5’ to 3’ direction and the lagging strand runs in the 3’ to 5’ direction. This allows for complementary base pairing and hydrogen bonds to form.
I can define the term gene as a set of instructions to build a protein.
Genes are inherited, help determine your traits, are sections of DNA that encode the structures of proteins, and are important structurally and functionally. A gene is a section of DNA that contains the code for a specific protein.
Gene expression is the specific, observable protein produced according to this genetic code.
Proteins are sequences of amino acids. The sequence of amino acids is found encoded in a gene. Proteins have four roles including structure building, transport channels, enzymes, and signaling.
I can explain what geneticists mean when they say replication is semiconservative.
Semi-conservatively means that each daughter double helix has some parent DNA and some DNA that has been newly synthesized.
I can describe the processes of strand separation, synthesizing daughter DNA, checking for errors and untangling the DNA in terms of the relevant enzymes involved and the steps in each process.
Separating The Strands
- Helicase binds to the origins of replication and begins to unwind the helix and separate the strands, breaking hydrogen bonds.
- Gyrase cuts the strands to temporarily allow relief from the tension building up that could cause twisting and tangling.
- Single-stranded binding proteins prevent the hydrogen bonds from reforming, which they have a tendency to do.
Building Complementary Strands
- Primase anneals RNA primer because polymerase cannot build DNA from scratch. They need a 3’ OH to add NTP to the developing strand. RNA primase does this.
- Polymerase III copies each strand, once continuously on the leading strand and in Okazaki fragments on the lagging strand.
- DNA polymerase adds free nucleoside triphosphates (NTP) in the 3’ to 5’ direction.
- Polymerase I replaces the primers with DNA nucleotides.
Checking For Errors
- DNA polymerase II goes along the double helix and checks for inconsistencies. Any time it finds one it replaces the faulty nucleotide with the correct one.
- DNA polymerase II also replaced the RNA primer base with DNA so the entire molecule is DNA.
- Okazaki fragments on the lagging strand need to be sealed by ligase.
- Ligase seals everything up like glue.
Untangling Daughter DNA
- As the daughter’s DNA is synthesized it has a tendency to entangle. Since each cell needs its own complete copy of the DNA to function, the last step in the process is to untangle the daughter strands.
- Topoisomerases are responsible for this process.
I can explain what Okazaki fragments are and use this explanation to distinguish between the leading and lagging strands.
Okazaki fragments are short sections of DNA built on the lagging strand.
The leading strand runs in the 5’ to 3’ direction and the lagging strand runs in the 3’ to 5’ direction.
Because the primer can only move in a 5’ to 3’ direction, it must move in the opposite direction of the helicase on the lagging strand. This means that fragments will appear as it cannot contiunly move with the helicase. These fragments need to be sealed by ligase.
I can distinguish between the coding and template strand of DNA.
One strand of DNA, the template strand, acts as a template for RNA polymerase. As it “reads” this template one base at a time, the polymerase builds an RNA molecule out of complementary nucleotides, making a chain that grows from 5’ to 3’. The RNA transcript carries the same information as the non-template (coding) strand of DNA, but it contains the base uracil (U) instead of thymine (T).
I can identify the three phases of transcription (initiation, elongation and termination) and describe what happens during each phase to produce the mRNA transcript.
Initiation
- Special regions of DNA called promoters help the RNA polymerase identify the location of genes.
- Special molecules that help the polymerase enzyme identify and bind to promoter regions.
- Their presence during specific points in development turns genes associated with cell specialization on.
Elongation
- RNA polymerase synthesizes the mRNA transcript in the 5’ to 3’ direction using similar base pairing rules as DNA.
- RNA polymerase unwinds and rewinds the DNA double helix as synthesizes the mRNA transcript.
- Only about 10-20 DNA bases are exposed at any one time.
Termination
- RNA polymerase encounters a sequence of DNA nucleotides called the termination sequence.
- The presence of cytosine and guanine in the termination sequence creates a hairpin that pries the RNA polymerase enzyme off the DNA molecule.
I can identify the post-transcriptional modifications made to eukaryotic mRNA:
Post-Transcriptional Modification
Before the mRNA transcript can leave the nucleus it must be modified.
Introns are removed.
Exons are spliced together.
A 5’ methyl cap is added.
A 3’ poly-A tail is added.
I can identify the three phases of translation (initiation, elongation and termination) and describe what happens during each phase to produce a polypeptide.
Initiation
- The small ribosomal subunit binds to the mRNA transcript at the 5’ end and searches for a start codon.
Elongation
- The ribosome moves along the mRNA transcript in the 5’ to 3’ direction.
- As each successive codon is read, a tRNA with a corresponding anticodon brings its amino acid into the A-site.
Termination
- The ribosome encounters a codon that does not encode an amino acid, instead it signals the small and large subunit to separate and release the polypeptide strand.
I can distinguish between a point mutation and a frameshift mutation and identify specific types of point mutations (e.g. silent, missense, nonsense, start-loss, etc.) and frameshift mutations (i.e. insertions and deletions).
Point mutations include silent, missense, nonsense, and start loss.
- Silent mutations are when a base pair changes, but the amino acid stays the same.
- Missense mutations are when a single base pair changes causing the amino acid to change.
- Nonsense mutations occur when a premature stop codon is coded when a single base pair changes.
- Start loss mutations occur when the start codon is changed by a single base pair mutation.
Frameshift mutations include insertion and deletion. This is serious because all amino acids downstream of the mutation change.
- Insertion mutations occur when a base pair is inserted into a sequence jumbling everything else up.
- Deletion mutations occur when base pairs get deleted and mess up all other sequences.
I can describe the possible consequences of different kinds of mutation (e.g. a missense mutation that changes a polar amino acid to a non-polar amino acid will change the way the protein folds once it is synthesized).
Beta hemoglobin is what is found in sickle cell anemia. It forms large chains within blood cells that change the shape of the cell into a sickle cell. Normally the glutamic acid is charged in hydrophilic, the mutant type becomes valine which is nonpolar and hydrophobic causing issues.
I can write a complementary DNA sequence given a DNA sequence.
A and T
C and G
I can write an mRNA sequence given the template strand of DNA.
mRNA is the opposite of the DNA strand.
U instead of T.
I can write tRNA anticodons given the mRNA codons.
The opposite of the mRNA still using U instead of T.
I can translate mRNA codons to amino acids.
Using the codon chart, write the three letters that correspond to the codons.
What is a gene?
Genes are inherited, help determine your traits, are sections of DNA that encode the structures of proteins, and are important structurally and functionally. A gene is a section of DNA that contains the code for a specific protein.
Gene expression is the specific, observable protein produced according to this genetic code.
What is a protein?
Proteins are sequences of amino acids. The sequence of amino acids is found encoded in a gene. Proteins have four roles including structure building, transport channels, enzymes, and signaling.
