From gene to protein

Premedical biology

RNA

chemically similar to DNA, except it

contains ribose instead of deoxyribose and

has uracil instead of thymin

RNA molecule genes (eukaryotic) are

thousands nucleotides long

almost always consist of a single strand

less stable

RNA

some molecules are able to self-replicate

mistakes in replication – variability =

differentiation of RNA

family of closely related RNA sequencies

some molecules are able to self-catalysate

First genes were RNA molecules that polymerized

abiotically and replicated themselves

autocatalytically

Ribosyms

auto-replicating activity

RNA molecules with enzymatic activity

(ribosome, spliceosome)

Coenzymes

non-protein components in enzymes

many of them are derived from nucleotides

some coenzymes are ribonucleotids,

rRNA, mRNA

Transcription • Synthesis of RNA under the direction of DNA

• Information is simply copied from one to another

according to complementarity of bases

• enzyme RNA polymerase

• the beginning = promotor and initial code

• transcription factors, terminator

Promotor

Typical promoter region for a protein-coding eukaryotic gene.

• the template strand is used as a template for RNA

synthesis

• The transcript is pre-mRNA primary transcript (eukaryotic

cells)

• 7methyl Guanosin cap is added immediately to 5‘ end

• for protection from degradation by hydrolytic enzymes and

„attach“ sign for ribosomes

• poly(A) tail - polyadenylation of 3‘ end

• inhibit degradation of the RNA

RNA processing

RNA processing

• exons = encoding parts• introns = non-encoding parts cutted out• cut and paste job = splicing • during the RNA processing is created messenger RNA –

mRNA • snRNPs = spliceosome• Regulation

Genetic code nucleotide triplets specify amino acids

• 4 nucleotides specify 20 amino acids

• triplet code – three nucleotide

• according to base-pairing rules the mRNA base

triplets are called codons

• shared by the simplest bacteria after the most

complex plants and animals

• genetic code is almost universal

• the genetic code must have evolved very early

in the history of life

• In bacteria is transcription

and translation coupled

at the same time

• translation of eukarytes

occurs in cytoplazm

• Each codon along mRNA specifies which one of

the 20 amino acids will be incorporated

• AUG for methionin and

it is Initial codon

termination codons:

UAG, UGA, UAA

(stop signals)

• 61 of 64 triplets code for 20 amino acids

• There is redundancy, and it is not random

• codon of the same amino acids differ in third base

of triplet

• one tRNA exist for each mRNA codon, but number

of tRNA is 45, some tRNA have anticodons, that can

recognize two or more different codons.

• correct a reading frame

tRNA

• mRNA – series of codons

• Interpreter is transfer RNA

– tRNA

• transfer amino acid to a

ribosome

• nucleotide triplet called

anticodon (in tRNA) links a

particular mRNA codon

• amino acid is added to the growing end of a

polypeptide chain in ribosome

• amino acid is joined to tRNA by specific enzyme aminoacyl-

tRNA synthetase - 20 these enzymes

• L-shape of tRNA

three-dimensional

structure

Aminoacyl tRNA-

synthetase

joins a specific amino acids

to a tRNA

- covalent attachment of

amino acids to its tRNA

- hydrolysis of ATP

Ribosomes

• facilitate specific

coupling of tRNA

anticodons with mRNA

codons

• subunits: proteins

and ribosomal RNA

• made in nucleolus

(eu)

Translation

Initiation, elongation, termination

specific fators, GTP

Peptide bond – new amino acid

and carboxyl end

Iniciation factors,

Elongation factors

Termination

Polyribosomes

Polyribosomes (or polysomes) are a cluster of

ribosomes, bound to a mRNA molecule, read one strand

of mRNA simultaneously.

Coupled

transciption and

translation in

bacteria

Comparing protein synthesis in prokaryotes and eukaryotes

• very similar but with certain differencies

• different polymerases, euk. depends on transcription

factors

• ribosomes are different – simultaneously transcribe and

translate the same gene and protein can quickly diffuse

• nuclear envelope segregates transcription and

translation

• processing stages provides ways to regulate and coordinate

proteosynthesis and gene expression in the eukaryotic cells

From polypeptide to functional protein

• Coiling and folding are spontaneous actions

• Genes determines the primary structure, the primary

structure determines conformation

• Chaperones

• Posttranslational modifications: certain amino acid are

modified by attachment of sugars, lipids, phosphate

groups……………..

• Two or more polypeptides may join to become the

subunits of a protein

Primary structure: the amino acid sequence

Secondary structure: local structures stabilized by hydrogen bonds.

The most common examples are the alpha helix, beta sheet and

turns.

Tertiary structure: the overall shape of a single protein molecule; most

commonly the formation of a hydrophobic core, but also through salt

bridges, hydrogen bonds, disulfide bonds. The tertiary structure is

what controls the basic function of the protein.

- as synonymous with the term fold

Quaternary structure: the structure formed by several protein molecules

(polypeptide chains), usually called protein subunits in this context,

which function as a single protein complex.

Protein structures

3-dimensional

structures of

protein

Thank you for your attention

Campbell, Neil A., Reece, Jane B., Cain Michael L., Jackson, Robert B., Minorsky, Peter V., Biology, Benjamin-Cummings Publishing Company, 1996 –2010.