Nucleic Acids, Protein Synthesis & Cell Division Flashcards
True or false;
Nucleic acids are organic
True
Describe the structure of nucleotides
- has a five carbon sugar, nitrogenous base and phosphoric acid
- Those containing ribose, are called ribonucleic acid, and those containing deoxyribose called deoxyribonucleic acid
- Each nucleic acid contains four bases two are purines, and two are pyrimidines
- Purines; Adenine, Guanine
- Pyrimidines; Thymine, Cytosine, Uracil (in place of thymine in RNA)
- Phosphoric acid gives the nucleic acids their acid character
Describe the process of formation of a nucleotide
- A pentose sugar is joined to phosphoric acid and then to a nitrogenous base in a condensation reaction in which two water molecules are lost
- The phosphate group is joined at C-5 and the nitrogenous base is joined at C-1
Describe the structure of DNA according to Watson & Crick
- DNA is made up of two polypolynucleotide chains
- The nucleotides have nitrogenous bases such as Adenine and Guanine (purines) and Cytosine and thymine (pyrimidines)
- They also have the pentose sugar deoxyribose
- Phosphoric acid is also a constituent of nucleotides situated on C-5 of the pentose sugar
- There is complementary base pairing between the nitrogenous bases which are bonded by hydrogen bonds
- Adenine is joined by two hydrogen bonds to Thymine while guanine is joined by three hydrogen bonds to cytosine.
- The nucleotides are joined by phosphodiester bonds
- Thus DNA has a sugar-phosphate backbone
- The two polynucleotide chains run in opposite directions (anti-parallel). One in the five prime to three prime direction, and the other, in the three prime to five prime direction
- DNA has a double helix structure
- The hydrogen bonds easily break and form for replication
- The width between the backbones is equal to the width of a base pair
Describe the semi conservative theory
From the original DNA strand, two similar copies of DNA are formed containing half the original DNA and half being the newly formed polynucleotide chain
(The old chains are templates for the new DNA strands)
Describe the process of DNA replication
- The enzyme DNA Helicase catalyses the unzipping of the two polynucleotide chains, exposing the nitrogenous bases on each chain
- Each polynucleotide chain serves as a template for formation of a new DNA strand
- Single-stranded binding protein stabilizes the single strands and prevents them from recoiling
- Topoisomerase enzyme catalyses the reduction in tension in the chain as unwinding continues
- RNA primase enzyme catalyzes the addition of an RNA primer, which initiates the process
- DNA polymerase catalyzes the removal of the RNA primer and addition of nucleotides to the exposed bases following the complementary base pairing rule
- The new polynucleotide chain is synthesized in the five prime to three prime direction
- It also proofread the newly formed DNA to remove any errors
- It repairs the DNA where necessary
- DNA ligase enzyme joins the Okazaki fragments together on the lagging strand
Give the similarities between the lagging strand and the leading strand
- both are templates for DNA replication
- Both form half of the new DNA
Give the differences between the leading strand in the lagging strand
LEADING
- runs in the three prime to five prime direction
- The polynucleotide formation is continuous
- Okazaki fragments are absent
- DNA ligase is not involved
LAGGING
- runs in the five prime to three prime direction
- The polynucleotide formation is discontinuous
- Okazaki fragments are present
- DNA ligase is involved
What are the adaptations of DNA to its functions?
- strong covalent phosphodiester bonds for stability
- Anti-parallel for complementary base pairing
- Double stranded for stability
- Double helix to protect the bases and hydrogen bonds
- Long to store much information
- Double helix structure, compact to fit in the nucleus
- Base sequence allows information to be stored
- Double stranded for replication to occur semi conservatively
- Complementary base pairing for identical copies to be made
- Weak, hydrogen bonds, enable unwinding of stands to occur
- Many Hydrogen bonds for stability
Why is DNA confined to the nucleus?
- to prevent alteration by chemical reactions in the cytoplasm
- It is too large to fit through the nuclear pores
What is the use of ribosomes in proteins synthesis?
They are a point of anchorage for the tRNA and mRNA molecules
What is transcription?
This is the mechanism by which the base sequence of a section of DNA representing a gene is converted into the complementary base sequence of mRNA
Where does transcription occur?
It occurs in the nucleus
Where does translation occur ?
Cytoplasm, Ribosome
What is translation?
This is the mechanism by which the sequence of bases in an mRNA molecule is converted into a sequence of amino acids in a polypeptide chain
What is the importance of transcription?
- DNA is too large to fit through the nuclear pores yet mRNA being small can readily exit the nucleus
- DNA contains many codes that aren’t always needed at a given time so mRNA only carries the code needed to make specific proteins
Describe the process of transcription
[start by defining transcription]
[State where proteins synthesis happens, and where transcription happens and why]
- The DNA double helix unwind by breakage of the relatively weak hydrogen bonds between the bases of the two strands
- Single strands of DNA are exposed
- One strand is selected as the template strand for the formation of a complementary single strand of mRNA
- Under the influence of RNA polymerase, and according to the rules of base pairing between DNA and RNA, that is A & U and G & C the mRNA molecule is formed through linking of free nucleotides
- When the mRNA molecules have been synthesized, they leave the nucleus via the nuclear pores, and carry the genetic code to the ribosomes for protein synthesis
- When sufficient numbers of mRNA molecules have been formed from the gene, the RNA polymerase molecule leaves the DNA and the two strands zip up again, reforming the double helix
Describe the process of translation
- Binding of mRNA to ribosome
- Amino acid, activation, and attachment to tRNA
- Polypeptide, chain initiation
- Chain elongation
- Chain termination
- Fate of the polypeptide chain
