Proteins

Structure and size: proteins are linear, unbranched polymers constructed from 20 different α-amino acids that are encoded in the DNA of the genome. All living organisms use the same 20 amino acids and the same genetic code. Proteins are large molecules with molecular weight ranging from 10 to 50 kdal for single-chain proteins. Multichain proteins of 150 to 200 kdal are frequently encountered.

Proteins serve a wide range of functions in living organisms. They are involved in the following:

• enzymatic catalysis (all known enzymes are proteins);

• transport and storage of small molecules and ions;

• systematic movements (both striated and smooth muscle are composed chiefly of protein, as are structures involved in the motility of certain free-living cells;

• the structure of skin and bone (collagen, the most abundant protein in body, gives these structures high tensile strength);

• the immune defense system (antibodies are specialized proteins recognizing self and nonself);

• hormonal regulation (some hormones are proteins; the cellular receptors that recognize hormones and neutrotransmitters are proteins);

• control of genetic expression (repressor molecules in bacteria are proteins that suppress certain DNA sequences; protein initiation and termination factors serve in the transcription phases of gene function).

Proteins show an exquisite specificity of biologic function – a consequence of the uniqueness of the three-dimensional structural shape, or conformation, of each protein. In humans, disease states are often related to the altered function of a protein. This is due to an anomaly in the structure of the protein, which in turn may be due to a deficiency in its synthesis.

Amino acids. The fundamental units of protein polymers are α-amino acids. They are composed of an amino group, a carboxyl group, a hydrogen atom, and a distinctive side chain, all boned to a carbon atom. One of the 20 amino acids, proline, is an imino acid, not an α-amino acids as are the other 19. A few other amino acids are found in a number of proteins but are not coded for in DNA; they are derived from one or another of the 20 fundamental amino acids after these have been incorporated into the protein chain (post-translational modification).

Peptides and polypeptides. The peptide bond is the bond formed between the α-carboxyl group of one amino acid and the α-amino group of another. It is formed by removal of the elements of water. The process is highly endergonic and requires the concomitant hydrolysis of high-energy prosphate bonds. The peptide bond is a planar structure with the two adjacent α-carbons, a carbonyl oxygen, and α-amino-N and its associated H atom, and the carbonyl carbon all lying in the same plane. The – CN – bond has a partial double-bond character that prevents rotation about the bond axis. The linking together of many amino acids by peptide bonds produces polypeptide chains. Amino acids, when in polypeptide chains, are customarily referred to as residues. Protein polypeptide chains are typically more than 100 amino acid residues long. Smaller peptides, however, are common and often have important biologic roles. By convention, peptide structures are written from left to right, starting with the amino acid residue having a free α-amino group (the so-called N-terminal amino acid) and ending with the residue having a free α-carboxyl group (the C-terminal). Either the three-letter abbreviations of the single-letter abbreviations are used.

13. Game. Sentence Race

1. Prepare a list of review vocabulary words.

2. Write each word on two small pieces of paper. That means writing the word twice, once on each paper.

3. Organize the pieces like bundles, 2 bundles, 2 sets of identical words.

4. Divide the class into 2 teams. Get them to make creative team names.

5. Distribute each list of words to both teams. Every student on each team should have a paper.  Both teams have the same words.

6. When you call a word, 2 students should stand up, one from each team. The students must then run to the blackboard and race to write a sentence using their word.

The winner is the one with a correct and clearly written sentence.

14. Translate the text into English using the words you have learned.

Наночастицы.

Современная тенденция к миниатюризации показала, что вещество может иметь совершенно новые свойства, если взять очень маленькую частицу этого вещества. Частицы размерами от 1 до 100 нанометров обычно называют «наночастицами». Так, например, оказалось, что наночастицы некоторых материалов имеют очень хорошие каталитические и адсорбционные свойства. Другие материалы показывают удивительные оптические свойства.

Удается добиться взаимодействия искусственных наночастиц с природными объектами наноразмеров — белками, нуклеиновыми кислотами и др. Тщательно очищенные наночастицы могут самовыстраиваться в определённые структуры. Такая структура содержит строго упорядоченные наночастицы и также зачастую проявляет необычные свойства.

15. Write down 5 questions based on the article.

16. Summarize the idea of the text. What information is new for you?

17. Role-play game.

“THE NANOWORLD” ROLE PLAY: This role play is to discuss and decide which is the most important part of the nanoworld. Team up with classmates who have been assigned the same role to develop your roles and discuss ideas and “strategies” before the role play begins.

Introduce yourself to the other role players before the role play begins.

Role A – a protein

Some of your benefits:

Proteins are the chief actors within the cell, said to be carrying out the duties specified by the information encoded in genes. Proteins make up half the dry weight of an Escherichia coli cell, whereas other macromolecules such as DNA and RNA make up only 3% and 20%, respectively.

Why you are better than the nucleic acids and the carbon nanotubes?

Role B – nucleic acids

Some of your benefits:

Nucleic acids are biological molecules essential for life, and include DNA (deoxyribonucleic acid) and RNA (ribonucleic acid). Together with proteins, nucleic acids make up the most important macromolecules; each is found in abundance in all living things.

a) Deoxyribonucleic acid is a nucleic acid that contains the genetic instructions used in the development and functioning of all known living organisms. The main role of DNA molecules is the long-term storage of information and DNA is often compared to a set of blueprints, since it contains the instructions needed to construct other components of cells, such as proteins and RNA molecules.