Nucleic Acids Flashcards
What is DNA?
genetic material that is contained in the chromosomes of the nucleus.
What does DNA consists of?
- two polynucleotide strands paired together and held by hydrogen bonds between the nitrogenous bases
- pairing bases: A and T, C and G (complementary pairing)
- nucleotides are joined by covalent bonds
State the definition of nucleotides
Repeating units linked together to form chains or strands.
What nucleotides contain?
- nitrogenous base (cytosine, guanine, adenine, thymine)
- sugar - deoxyribose (DNA) and ribose (DNA)
- phosphate
How to differentiate between the deoxyribose and ribose?
Ribose has hydroxyl (OH) group at position 2. However, Deoxyribose has hydrogen atom (H) at the same position.
What are pyrimidines in DNA?
types of base pairs
Explain the DNA replication
It is the duplication of DNA by making a copy of an existing molecule (interphase). It leads to creation of two molecules of DNA
- one composed of original strand
- the second one is newly synthesized strand (semi-conservative strand)
What are the models of DNA replication
- conservative
- semi-conservative
- dispersive model
Explain the semi-conservative model
two parental strands separate an each functions as the template of a new complementary strand.
Explain the conservative model of DNA replication
parental double helix remains intact (unbroken) and new copy is made.
Explain the dispersive model of DNA replication
each strand contains a mixture of old and newly synthesized parts.
What is the process of DNA replication?
- Unwinding the DNA molecule- hydrogen bonds holding the strands have to be broken. Helicase is the enzyme that holds strands apart while replication occurs.
- Creating the new DNA strands involves the activity of an enzyme known as DNA polymerase. Fresh nucleotides containing complementary bases align themselves opposite the exposed bases of the strands. DNA polymerase then forms covalent bonds, linking the phosphate of the new nucleotide to the sugar of the preceding nucleotide.
- Rewinding the DNA molecule- each of new double-helix. DNA molecules have one strand of the original DNA and new strand. Two DNA strands wind up into double helix.
What are Okazaki fragments?
small sections of DNA that are formed during the synthesis of the lagging strand during DNA replication.
What is the function of RNA primer?
added by DNA primase to synthesize the new strands of DNA
What are topoisomerases?
enzymes that regulate the overwinding or underwinding of DNA. for example gyrase
What is the function of DNA polymerase I?
filling the DNA gaps that arise during DNA replication.
What is the function of the DNA polymerase III?
binding nucleotides together and forming a new strand
The function of ligase
Joining DNA molecules together
define transcription
the genetic information of DNA is transcribed into a molecule of mRNA by complementary base pairing.
Define translation
Process of protein production using mRNA molecule as a guide.
Define central dogma
states that information passes from genes on the DNA to RNA copy
Steps of transcription
- After DNA polymerase binds to the promoter of the DNA, DNA strands unwind and polymerase initiates RNA synthesis at the start point.
- Initiation- DNA is unwinded and RNA transcript 5’ -> 3’ is elongated. DNA strands re-form a double helix.
- Termination- the RNA transcript is released and polymerase detaches from DNA.
What is the difference between the antisense strand and sense strand of DNA?
- antisense strand is the non-coding DNA strand of a gene. it serves as the template for producing messenger RNA
- sense strand is the one coding of mRNA, the strand will be synthesized with this strand as the template.
What is the post-transcriptional modification?
It helps the RNA molecule to be recognized by molecules that take part in the translation into proteins.
Steps of the post-transcriptional modification (nucleus)?
- When a split gene is transcribed into mRNA, newly formed mRNA contains sequences of introns and exons.
- Introns are removed and the remaining coding portions of mRNA are spliced together.
- The mRNA passes out into cytoplasm to ribosomes where it is involved in protein synthesis.
Difference between the exons and introns
exons carry genetic information but introns are the units of non-coding sequences, so they do not carry any genetic information.
How are amino acids activated?
They are combined with short lengths of different tRNA molecules involved in the protein synthesis. tRNA catalyzes an ATP- requiring reaction.
The process of translation
- Anticodon (tRNA) pairs with mRNA codon in the A site. Hydrolysis of GTP increases efficiently.
- tRNA calalyzes the formation of peptide bonds. This step removes the polypeptide from tRNA in the P site to tRNA in A site.
- tRNA is translocated to P site and tRNA in P site is moved to E site, where it is released.Next codon can be translated in A site.
What happens in the A site?
It carries/holds tRNA carrying the amino acids.
The function of P site
It holds the tRNA with the polypeptide chain
The function of E site
releases the protein (tRNA with polypeptide chain)