Caiet de Biologie

Table of Contents

Nucleic Acids

Nucleic Acids are biological molecules that store the genetical information. They are monomolecules and polymers.

Dexoyribonucleic acid
Ribonucleic adcid

Nucleotide = Phosphate group + Sugar + Bases
(for DNA, PG + Deoxyribose + A/C/G/T
for RNA, PG + Ribose + A/C/G/U)

Many nucleotides bind together to form a long strand known as the primary structure of DNA. The bond occurs between the sugar of the previous nucleotide and the PG of the next.

Two strands run parallel to each other but in opposite directions. Bases are connected together by hydrogen bonds. TA and CG are the only pairs (complementary base pairing).

Finally, the molecule will twist and fold in space to take a ribbon-like felix shape — secondary structure of DNA

DNA can be affected by factors in the environment like temperature. Increasing the temperature to 70-80°C causes the hydrogen bonds to break and the strands to separate.

However, decreasing the temperature slowly will cause the reformation of bonds and the production of renatured DNA

Hybrid DNA: genetical material produced by combining the DNA from two different sources e.g. insulin-making bacteria


Single stranded NA that has a few functions so it exists in different forms:

Viral RNA
The genetic material of a special group of viruses called Riboviruses.
Messenger RNA (mRNA)
carries the information about how to make a protein from the DNA in the nucleus to the ribosomes in the citoplasm
Transport RNA (tRNA)
transports aminoacids to the ribosome in order to be assembled into proteins. It has a typical leaf-like shape with two important parts:
  • acceptor for attaching to an aminoacid
  • anticodon for recognition with mRNA
Ribosomal RNA (rRNA)
connected to the ribosomes. Most of the RNA exists in this form in the cell.

DNA Replication

Each time a cell divides it needs to double the amount of DNA so that each daughter cell receives the same amount of genetical information.

  1. Parent DNA unwinds and unzips so that the two strands separate. Hydrogen bonds are broken by the enzime DNA helicase.
  2. Each of the old strands will act as a template to produce a new strand. New nucleotides are added based on the rule of complementarity between bases by the enzyme DNA polymerase.
  3. Finally, the strands will join together and form the helix shape. Hydrogen bonds are produced by DNA ligase.

Since the newly formed DNA molecules are made of an old strand and a new strand, the model for this kind of replication is called semi-conservative replication.

Genetic code and protein synthesis

The genetic code consists of 64 series of 3 bases (called codons) that code for the 20 aminoacids necessary to make proteins. Each codon codes for one specific aminoacid. However, there can be multiple codons coding for the same aminoacid. Three of these codons are stop codons.

Protein synthesis is a two-step process: transcription and translation.

  1. Transcription:
    • The mRNA attaches to a ribosome.
    • The ribosome reads the first codon and a tRNA will bring the correct aminoacid based on the complementarity of the codon on the mRNA and the anticodon on the tRNA
    • The ribosome reads the next codon and another tRNA brings the correct aminoacid.
    • The process goes on like this until a stop codon is met and the protein synthesis is over.

Genetic counseling

  • in case of a genetic disease in the family
  • belonging to a group that has a high risk of genetic disease
  • there is already a child with disease
  • the woman is over 38
  • a high-risk pregnancy

The counselor makes use of two methods to obtain information about a disease: genetic screening and pedigree analysis.

Pedigree analysis: a series of methods used to screen babies for mutations during pregnancy

Amniocentesis = the collection of amniotic fluid for screening

In vitro fertilization

  1. The woman receives a hormonal treatment to stimulate the production of egg cells
  2. Egg cells are collected and placed together with the sperm cells in a dish
  3. The fertilized egg cell is placed back into the uterus and pregnancy starts

Author: Marius Gavrilescu

Created: 2015-01-20 Tue 23:50

Emacs 24.4.1 (Org mode 8.2.10)