biochimie

BIOCHIMIE

NOTIUNI INTRODUCTIVE

Chimia apei

Molecula polara Formeaza legaturi de hidrogen a caror tarie depinde de starea de

agregare Solvent foarte bun

pH

Apa tinde sa disocieze in H+ si HO-

[H+] > [HO- ] => acid

pH = - log [H+] Variaza intre 0-

14

Molecule organice

Grupe functionale

GLUCIDE

Cunoscute si sub denumirile de: hidrati de carbon, zaharide

Formula generala Cn H2n On ou (CH2O)n ex. C6H1206

Pot fi clasificate in: Monozaharide

trioze (3C) Pentoze (5C): ribose (in acizi nucleici ) Hexoze (6C: C6 H12 O6 )

In cazul hexozelor, cele mai importante sunt: glucoza, fructoza si galactoza

Toate au formula bruta: C6H12O6

Rolul glucidelor

Rezerve de energie de scurta durata (zahar);

Rezerve de energie de durata medie (glicogen)

Componente structurale ale unor celule (celuloza in peretii celulelor vegetale si chitina in exoscheletul unor insecte)

Hexoze

Glucoza

Dizaharide

Condensare – reactia dintre doua zaharide simple, cu formarea de dizaharide si a unei molecule de apa

Exemple: maltoza, zaharoza, lactoza Hidroliza unui dizaharid va da 2 zaharide

simple Reactii de condensare/hidroliza Glucoza + Glucoza -->Maltoza + H2O Glucoza + Fructoza --> Zaharoza + H2O

Glucoza + Galactoza -->Lactoza + H2O

Polizaharide Policondensarea monozaharidelor Ex. importante: amidonul, glicogenul si celuloza amidonul : polimer al glucozei, cu putine

ramificatii. Intalnit in plante (cartofi, cereale). Bogat in energie.

Glicogenul: preponderent la animale (ficat, muschi). Polimer al glucozei cu multe ramificatii. Forma de stocare a glucozei (substanta energetica) la nivel hepatic.

Celuloza : Similara amidonului si glicogenului. Preponderent in peretii celulelor vegetale. Nu prezinta ramificatii.

LIPIDE

Contin: C, H, O (P, N) 3 categorii de lipide

trigliceride fosfolipide steroizi

Rolul lipidelor

Sunt in special depozite energetice de lunga durata Animalele transforma excesul de zaharide (atunci

cand capacitatea de stocare sub forma de glicogen este depasita) in grasimi

Grasimile stocheaza 9.3 Kcal/g, in timp ce carbohidratii pot stoca doar 3.79 Kcal/g. Insolubile in substante polare ca apa

Componente structurale (fosfolipidele in membrana celulara)

“Mesageri" (hormoni), jucand un rol important in comunicarea intercelulara

Trigliceride

Trigliceride (rezerve energetice de durata )Sunt formate din glicerol + 3 acizi grasi

Acizi grasi

Acizii grasi pot fi saturati -fara legaturi duble intre atomii

de C nesaturati – prezinta legaturi duble; pot

fi saturati prin aditia de H2 suplimentarex. acid gras saturat: C16= acid

palmitic

Fosfolipide

Structura similara cu cea a trigliceridelor Prezinta in plus o grupare fosfat Aceste grupe se pot ioniza, astfel

molecula va prezenta un capat polar foarte solubil in apa (hidrofil) si un capat nepolar, insolubil in apa (hidrofobe).

Sunt constituenti fondamentali ai membranei celulare

Steroidzii

Sunt lipide complexe, avand in structura lor un nucleu sterolic

Au importanta biologica mare, deoarece fac parte din membrana celulara, careia ii asigura coeziunea

Intra in compozitia colesterolului si a unui numar mare de hormoni: estrogeni, progesteron, testosteron, cortisol, etc.

Colesterolul

Are multe utilizari biologice, cum ar fi: membrana celulara, teaca neuronilor, etc.

Excesul de colesterol se leaga de aparitia aterosclerozei care duce la ingrosarea si pierderea elasticitatii arterelor.

LIPOPROTEINE

Aminoacizii (AA).

Prezinta O grupare acida sau carboxilica (-COOH)O grupare amino (-NH2) Un radical (R).

Exista 20 AA diferiti.

Aminoacizi

Legatura peptidica

-CONH- Pot exista si legaturi intre atomii de sulf

(disulfidice ) in cazul metioninei si cisteinei Polimerizarea aminoacizilor poate duce la

formarea de: dipeptide tripeptide polipeptide protéines.

Proteinele

Functiile de control se realizeaza prin intermediul enzimelor si al hormonilor.

Enzimele sunt catalizatori organici Proteinele structurale intra in alcatuirea

membranelor celulare, tesutului muscular, etc.

Proteinele

Posibilitatea combinatiilor face ca numarul lor sa fie aproape nelimitat

Structurile proteice: Primara : secventa aminoacizilor Secundara: interactiuni intre legaturile peptidice. Structuri

helix Tertiara: interactiuni intre radicali. Proteina are o forma

tridimensionala Cuaternara : interactiuni intre diferite unitati ale proteinelor,

ceea ce le ofera o conformatie definitiva ( globulaire, spiralée etc.)

Structura unei proteine poate fi alterarta prin actiunea unor factori fizici sau chimici, care actioneaza asupra diferitelor structuri, modificand si proprietatile biologice

Structura proteinelor

Structura primara

Reprezinta secventa de amino acizi which is directly related to the sequence of information in the RNA molecule, which in turn is a copy of the information in the DNA molecule.

Changes in the primary structure can alter the proper functioning of the protein. Protein function is usually tied to their three-dimensional structure. The primary structure is the sequence of amino acids in a polypeptide

The secondary structure is the tendency of the polypeptide to coil or pleat due to H-bonding between R-groups. The tertiary structure is controlled by bonding (or in some cases repulsion) between R-groups. Many proteins, such as hemoglobin, are formed from one or more polypeptides. Such structure is termed quaternary structure. Structural proteins, such as collagen, have regular repeated primary structures. Like the structural carbohydrates, the components determine the final shape and ultimately function. Collagens have a variety of functions in living things, such as the tendons, hide, and corneas of a cow. Keratin is another structural protein. It is found in fingernails, feathers, hair, and rhinoceros horns. Microtubules, important in cell division and structures of flagella and cilia (among other things), are composed of globular structural proteins.

ACIZI NUCLEICI

Nucleic acids are polymers composed of monomer units known as nucleotides. There are a very few different types of nucleotides. The main functions of nucleotides are information storage (DNA), protein synthesis (RNA), and energy transfers (ATP and NAD). Nucleotides consist of a sugar, a nitrogenous base, and a phosphate. The sugars are either ribose or deoxyribose. They differ by the lack of one oxygen in deoxyribose. Both are pentoses usually in a ring form. There are five nitrogenous bases. Purines (Adenine and Guanine) are double-ring structures, while pyrimidines (Cytosine, Thymine and Uracil) are single-ringed.

Deoxyribonucleic acid (better known as DNA) is the physical carrier of inheritance for 99% of living organisms. The bases in DNA are C, G, A and T. We will learn more about the DNA structure and function later in the course (click here for a quick look [actually take all the time you want!] ;)). DNA functions in information storage. The English alphabet has 26 letters and over 50,000 words. DNA has 4 letters (C, G, A, and T) and 20 words (the 20 amino acids) that can make an infinite variety of sentences (polypeptides

ribonucleic acid (RNA) Nucleic acid containing ribose sugar and the base Uracil; RNA functions in protein synthesis. The single starnded molecule transcribed from one strand of the DNA. There are three types of RNA, each is involved in protein synthesis. RNA is made up nucleotides containing the sugar ribose, a phosphate group, and one of four nitrogenous bases (adenine, uracil, cytosine or guanine). PICTURE