Chapter 6- Nucleic Acid and Protein Synthesis Flashcards
What does DNA stands for?
Deoxyribose nucleic acid
What did Messelson and Stahl’s experiment conclude?
Their experiment proved that DNA replication is semi conservative, where one half of the DNA strand goes into each new cell
Each DNA strand acts as a template for complementary base pairing and each new cell contains half old and half new DNA
What is DNA molecule made of?
DNA is made of individual nucleotides(sub-units) which is also called polynucleotide/nucleic acid
A nucleotide consists of 3 sections:
- Deoxyribose sugar(pentose)
- A base, either A, U, T, C, G
- A phosphate group
What are purines and pyrimidines?
Purines are the larger molecule and consists of 2 rings
- Adenine
- Guanine
Pyrimidines are the smaller molecule and consists of 1 ring
- Thymine
- Cytosine
- Uracil
Explain the structure of a polynucleotide
The phosphate group and pentose sugar forms the backbone of a DNA molecule
Adenine is always paired with thymine and forms 2 hydrogen bonds
Guanine is always paired with cytosine and forms 3 hydrogen bonds
The two polynucleotide chain run in opposite direction. 3 prime(3’) and 5 prime(5’) are the ends of the each chain- the humbers refer to the expose carbon number of the pentose sugar
Explain how a DNA is replicated
The DNA unwinds and unzips(the hydrogen bonds between the bases break)
New nucleotides attach to the exposed bases, but only the complementary bases
Before bonding, these nucleotides have 3 phosphate groups attached, but they are removed during attachment
Explain the role of the helicase, polymerase and ligase enzymes during DNA replication
DNA helicase
- unzips the original DNA molecule to expose the bases
DNA polymerase
- forms hydrogen bonds between the complementary adjacent base pairs
DNA ligase
- link the pentose sugar and phosphate group with the next nucleotide to form the backbone of the DNA molecule
How does mutation occur?
Mutations occur in the DNA, but the impact is seen on the protein and it can lead to a change in the phenotype of an organism
A vast majority of mutations are negative(may cause disease or death)
Some are neutral(makes no difference to the cell or organism) and they are callsed silent mutations
Some may be positive(makes a new protein or changes the active site of an enzyme to fit the substrate better)
How does transcription and translation occur?
Transcription is the process where the DNA strand unwinds and unzips(DNA helicase) and a single strand of mRNA is copied from the DNA code. This process occurs inside the nucleus
This process happens as DNA is too large to pass through the nuclear membrane but the mRNA is small enough to pass through it. The codes on the mRNA is read as triplet codes(codons) and each codon codes for a different amino acid
Translation is the process where the mRNA is read and a primary structure of amino acid is produced. This process occurs at the ribosomes and/or rough ER
The ribosomes have tRNA at its large subunits. tRNA has the anticodons that couples with the codons on mRNA. At the other end of the tRNA is the specific complementary amino acid
At the ribosome, the mRNA passes between the large and small subunit, and come into contact with the anticodons. As the codes are read, amino acids are bonded(peptide bond formed through condensation reaction/polymerisation) and a primary sequence is formed
Afterwards, the mRNA breaks down(uracil makes it unstable) and the tRNA floats around to find proteins
What does an ATP structure looks like and how does it work as an energy source?
An ATP stands for adenosine triphosphate
ATP is made up of an adenine base, a pentose sugar and 3 phosphate groups. It is almost identical to the adenine nucleotide
ATP releases one phosphate group to form ADP and releases 30.5 kJ of energy during the process
ADP releases one phosphate group to form AMP and releases 11.5 kJ of energy during the process
