1. The gene: structure, function and location

2. Evolution of knowledge about gene
G. Mendel
Hereditary factors
W.Johannsen, 1909
The gene – hereditary unit located in chromosomes
G.W.Beadle, E.L.Tatum, 1945
Hypotheses “One gene – one enzyme”
Ingram, 1957
Hypotheses “One gene – one polypeptide”
Actual concepts
The gene – a sequence of DNA responsible for synthesis of macromolecules

3. DNA Contains information about RNAs and proteins.
Double stranded molecule;
Polynucleotide chains;
Contains information about RNAs and proteins.

4. Genetic code - DNA: Letters: A, G, C, T
Words (one codon  one amino acid):
AAG - lys
AGC - ser
GCA - ala
TTC – phe
TAG – stop
Phrases: 5' AAGAGCGCATTCTAG 3'
lys – ser – ala – phe – stop

5. Gene expression DNA mRNA Protein
5’-ATTGCAAGATTACCATGT-3’ Coding strand (untranscribed)
3’-TAACGTTCTAATGGTACA-5’ Template strand (transcribed)
Transcription (RNA polymerase)
5’-AUUGCAAGAUUACCAUGU-3’ mRNA
Translation (tRNA, ribosomes)
Leu – Ala – Arg – Leu – Pro – Cys polypeptide

6. Definition:
Gene – a fragment of polynucleotide chain of DNA which contains information about synthesis of:
one polypeptide or
several polypeptides or
a functional RNA (rRNA, tRNA, snRNA)

7. Gene expression
rRNA
tRNA
mRNA
DNA
Protein

8. 2nd class genes = structural
Classification:
1st class genes
encode 5,8S, 18S and 28S rRNA;
2nd class genes = structural
encode mRNA  proteins;
3rd class genes
encode tRNA, 5S rRNA.

9. Gene’s localization: Genes are located in DNA molecules;
Genes consist of unique or repeated sequences;
The genes from one molecule of DNA are separated by non-coding sequences – spacers;
There are no morphological borders each gene has only functional frontiers;
The length of genes is different.

12. - The dimensions of human genome – 3,164 x 109 bp - 2% of human genome encode for proteins - Number of genes Chromosome 1 contains – 3380 genes - Chromosome Y contains – 397 genes - Known function – 50% human studied genes - Average length of gene – 3000 bp - gene for β-globin – 1,5 kb - gene for insulin – 1,7 kb - gene for catalase – 34 kb - gene for dystrophin - 2,4 Mb

13. Distribution of human genes by length
Length, kb %
Up to 10
23,3
10-25
35,6
25-50
20,2
51-100
13,0
6,7
over 500
1,2

14. General structure of the transcription unit
Central region – coding region;
Regulatory regions:
proximal – PROMOTER
distal – TERMINATOR
± Modulation sequences

15. Functions: At molecular level At cellular level At tissue level
control of polypeptide’s synthesis  functional protein
At cellular level
production of a normal cellular structure, metabolic chain, signaling chain, etc.
At tissue level
realization of a specific function (respiration, digestion, contraction, etc.)
At organism level
a specific trait (character)

16. Each cell contains a complete set of genes
( pairs of genes in all 46 molecules of DNA)
Expression – only 10% of all genes
Permanent expression
rRNA genes
tRNA genes
House keeping genes
Temporary expression depending on:
- tissue;
- ontogenetic period;
- cell cycle period;
- environment factors
Absence of expression
pseudogenes

17. The 2nd class genes = structural (25% of nuclear DNA)
Encode one or several polypeptides;
Form monocistronic transcription units;
Have a mosaic structure (exon/intron);
Could be transcribed:
In all cells (house keeping genes)
Specific, depending on type of cell, age, factors;
Are transcribed by RNA-polymerase II in a primary transcript – pro-mRNA;
Are numerous, usually unique and heterogeneous;
May form repetitive or non-repetitive families of genes;
Present individual polymorphisms.

18. Types of structural genes
House keeping – genes that encode indispensable cell proteins, active in all cells, in all periods of life;
Tissue-specific – genes that encode for proteins require for tissue specialization;
Regulatory of ontogenesis;
Dependent on environment factors.

19. Gene families
Repetitive gene’s family: a family of identical genes
Non-repetitive gene’s family: a family of genes of related structure and usually related function

20. Peculiarities of the 2nd class genes structure

21. Initiation of transcription of the 2nd class genes
-10
-20
-30
-40 +1
+10
+20
+30
TAFs
RNA-polymerase II
TFIID
TFIIF
TFIIA
TFIIE
TFIIB

22. Regions of structural genes
Promoter:
TATA box (-20, -30)
CAAT box (-70, - 100)
Tissue-specific boxes( - )
Coding region:
site +1, leader sequence
exon1/intron/exon2/intron/.../exonn
Terminator
Site of polyadenilation
Enhancers and silencers

23. Promoter of the 2nd class genes
Controls the initiation of transcription:
Activation of gene;
Fixing of TF and RNA-polymerase II;
Identification of (+1) and transcribed strand;
Directing of RNA-polymerase II.
Is not transcribed;
In different genes promoters contain different specific boxes;
Mutations in promoter may induce gene inactivation.

24. Conservative boxes in structure of eukaryotic promoters
Sequence
Position
Length of bound DNA
Transcription factors
TATA-box
TATAAAA
- 30
10 p.n.
TBP
CAAT-box
GGCCAATCT
- 75
22 p.n.
CTF/NF1
GC-box
GGGCGG
- 90
20 p.n.
SP1
Octamer
ATTTGCAT
Oct1, Oct2

25. Structure of promoter in structural genes in eukaryotes
(2nd class genes)
Structure of promoter in structural genes in prokaryotes

26. Interaction promoter-enhancer

27. Exons Sequences of structural genes that encode polypeptide sequences;
Are found in pro-mRNA and mRNA;
Are transcribed and translated;
Each exon encodes a region of protein;
During alternative splicing some exons may be removed.

28. Introns Non-coding sequences of structural genes that separate exons;
Are found in pro-mRNA but not in mRNA;
Are transcribed but not translated;
During splicing all introns are removed;

30. Structure of terminator

31. Structure of transcription unit which contains rRNA genes in eukaryotes (1st class genes)
Promoter ( )
Gene 18S
Gene 5,8S
Gene 28S
Terminator n

32. Organization of the 3rd class genes Structure of 5S rRNA genes
Promoter – A box (+ 55) and B box (+ 80)
Genes for tRNA / rRNA 5S
Terminator n
Structure of 5S rRNA genes

34. Structure of operon in prokaryotes

35. Human mitochondrial genom

37. Mobile genetic elements = TRANSPOSONS
Type
Main gene
Type of transposition
Exemples
DNA transposons
Transposase
Transposition through excision or replication
Tn (bacterial)
P (Drosophila)
Retrovirus like transposons
Revers-transcriptase (revertase)
Transposition through RNA produced on the basis of promoters located in LTR
THE-1 (human)
Ty (yeast)
Retro-transposons
Transposition through RNA produced on the basis of neighbor promoters
L1 - LINEs

38. Biological role of transposons
Site-specific recombination
Individual polymorphism of DNA
Insertional mutagenesis
Genome instability  fragile sites in DNA
Evolution of genomes

39. Medical importance of transposons
Changes in structure / function of structural genes  genetic diseases (hemophilia B, epilepsy, retinita pigmentosum, etc)
Variability of pathogen agents  resistance to antibiotics and immune system