- Messages
- 22
- Reaction score
- 6
- Points
- 13
DNA and RNA are polynucleotides ,made up of long chains of nucleotides.A nucleotide consists of a pentose sugar,a phosphate group and an nitrogen-containing base
.A DNA molecule consists of two polynucleotide chains ,linked by hydrogen bonds between the bases.Adenine always bonds with thymine and cytosine with guanine
.RNA which comes in several different forms , has only one polynucleotide chain ,although this may be twisted back onto itself like in tRNA .In RNA the base thymine is replaced by uracil.
DNA molecules replicate during interphase .The hydrogen bonds between the bases break ,allowing free nucleotides to fall into position beside their complementary bases on each strand of the original DNA molecule .Adjacent nucleotides are then linked ,through their phosphates and sugars ,to form new strands .Two complete new molecules are thus formed from one old one ,each new molecule containing one old strand and one new .
The sequence of bases on a DNA code for a amino acids in a protein (or polypeptide) .Each amino acid is coded for by three bases .A length of DNA coding for one complete protein or polypeptide is a gene.
During protein synthesis , a complementary copy of the base sequence on a gene is made by building a molecule of mRNA against one DNA strand .The mRNA then moves to a ribosome in the cytoplasm.
tRNA molecules with complementary triplets of bases temporarily pair up with the base triplets on the mRNA ,bringing appropriate amino acids .As two amino acids are held side by side ,a peptide bond is formed between them .The ribosome moves along the mRNA molecule , so that appropriate amino acids are linked together , following the sequence laid down by the base sequence on the mRNA
That should pretty much sum up the whole chapter .Hope this helps!
Thank you soooo much !!! I wish u a good luck on the exam !