Molecular biology

Main Concepts of chapter-10

Molecular Biology

1- Genetic information control the inheritance of the characters and the development of the fertilized egg into an individual.

2- Genes are the units of genetic information.

3- Chromosomes are composed of DNA and proteins.

4- Evidences that DNA is the genetic material:
A- Bacterial transformation.
B- Bacteriophages.
C- The quantity of DNA in cells.
C- The base content of DNA in cells.
5- DNA is a polymer which consists of four monomers called nucleotides.

6- Each nucleotide consists of:
A- Nitrogenous base [purines or prymidines]
B- Ribose or deoxyribose sugar.
C- Phosphate group.

7- Adenine pairs to thymine and guanine pairs to cytosin through hydrogen bonds.

8- The replication of DNA needs a number of enzymes and proteins:
A- DNA helicase which moves along the double helix, separating the two strands
B- DNA polymerase which works only on the 3 to 5 template and it adds new nucleotides.
C- DNA ligase which joins pieces of DNA together.

9- All Biological polymers are damaged by:
A- The body heat.
B- The aqueous state inside the cell.
C- Various chemicals and radiations.

10- DNA in prokaryote is circular, its two ends are joined, it is attached to the plasma membrane at a point or more where douplication starts, it is not complexed with proteins, 100% coding sequences, there are some additional small circular DNA called plasmids.

11- DNA of Eukaryotes is organized into several chromosomes, each one contains a single DNA molecule which is associated with various protein (chromatin) these proteins may be:
A: histone proteins
B: Non- histone proteins.

12- Genome is the total of all the genes (DNA) in any body cell.

13- Any gene is a sequence of nucleotides.

14- DNA can be divided into:
A- Coding DNA which is responsible for the production of RNA and protein synthesis.
B- Non-coding DNA.

15- Transcription is to change the sequence of nitrogenous bases in a DNA strand into a sequence of nitrogenous bases in m-RNA strand.

16- There are three types of RNA:
A- Messenger RNA
B- Ribosomal RNA
C- Transfer RNA

17- Most of genes are present in only one copy or few copies in the genome, but sometimes some sequences of nucleotides are repeated which we call repetitive DNA or satellite DNA.

18- In 1960 it was discovered that the genes that make bacterial resistant against drugs transfer from one bacterium to another by plasmids.

19- Proteins are divided into two main groups:
A- Structural proteins
Fibrous proteins - collagens - keratins
B- Regulatory proteins - Enzymes - Antibodies - Hormones

20- Proteins are formed of un branched linear chains join between amino acids.

21- There are 20 different amino acids, which have the same basic structure

22- Amino acids are joined together by peptide bonds through dehydration reaction.

23- RNA is formed of a single strand, the sugar is ribose and pyrimidines bases are uracil and cytosine.

24- M.RNA has the following main parts:
A- Ribosome binding site (5 end)
B- Start codon [AUG]
C- Polyadenine tail (3 end)
D- Stop codon [UAA - UAG - UGA]
25- Ribosomes consists of 4 types of rRNA and about 70 kinds of polypeptides.

26- The production of ribosomes takes place in the nucleolus.

27- T.RNA carries amino acids from the cytoplasm to the ribosomes.

28- For each kind of amino acids there is a specific kind of t.RNA molecule that can recognize and transport it.

29- There are 2 sites on T.RNA:
A- The amino acid attachement site
B- The anti-codon.

30- The genetic code is the triplet sequence of nucleotides in DNA and it is transcribed into a complementary sequence in m-RNA which goes to the ribosome where it is translated into a sequence of amino acids in a poly-peptide (protein)

31- Protein synthesis passes through three main stages:
A- Initiation
B- Elongation
C- Termination

32- Nucleic acid hybridization:
- If DNA is heated to 100 ^o C the hydrogen bonds between base pairs are broken down and the two strands of DNA molecule are separated producing single stranded DNA.
- Hybridization technique is used in producing hybrid or mixed double helices, to tell if a particular gene is present in a genome, and also to determine the degree of relationship between two different species of living organisms.

33- Bacterial restriction enzymes are secreted by some strains of E-coli, they attack specific sequences of nucleotides in the viral DNA and break it down into useless fragments, the bacteria protect themselves from these enzymes with the help of modification enzymes which add or bind methyl groups to the recognition sites.

34- Several copies of a desired gene can be produced by splicing it to a molecule that carry it into bacterial cells, this carrier may be a phage or plasmid in case of prokaryotes and jumping genes in case of eukaryotes.

35- Recombinant DNA technology is the introducing of DNA from one organism into cells of another living organism.

36- Interferons are proteins that interfere with replication of viruses specially viruses with RNA genomes such as influenza and poliomyelities.

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