An Introduction To Genetics: Rifat Ali Kheshgi Student At Nwfp Agricultural University Peshawar Cell # 03139556067

An Introduction to Genetics RIFAT ALI KHESHGI Student at NWFP AGRICULTURAL UNIVERSITY PESHAWAR Cell # 03139556067

Human Genome ■

Genome structure ■ Chromosome/Gene/DNA

■

Protein Synthesis

■ Transcription

■

DNA Replication /Cell Division ■ Mitosis

■

and Translation

Mutations

and Meiosis

Human Genome

The Human Genome 9

■ The human genome is made up of 3 x 10 base pairs of DNA (haploid genome)

■ This contains 30,000 genes arranged on 46 chromosomes ■ Packaged within the nucleus of the cell

Chromosomes  Long strands of DNA packaged and compressed very tightly  Everyone has 2 copies of each chromosome 1 pair of each of the 22 ‘autosomes’ • plus XX for a female (46XX) • or XY for a male (46XY)

 DIPLOID GENOME

Chromosomes in Metaphase Telomere Short arm (p) Centromere

Long arm (q) Telomere

Genes – 30 000 ■

Segments of DNA code that provide the instructions for the manufacture of a protein by the cell

■

One gene encodes for one protein (or part of)

DNA (DeoxyriboNucleic Acid) 2 major functions  Direction of all protein synthesis  Accurate transmission of this information from one generation to the next Fundamental to  Cell metabolism  Cell division

Chromosomes and Inheritance ■ ■

1 from Mother, 1 from Father Eggs cells contain 23 chromosomes ■ ■

■

Sperm cells contain 23 chromosomes ■ ■

■

One of each autosome One X chromosome

One of each autosome One sex determining chromosome (an X or Y)

Haploid cells (cells containing only one copy of the genome)

Chromosomes and Inheritance ■ ■

1 from Mother, 1 from Father Eggs cells contain 23 chromosomes ■ ■

■

Sperm cells contain 23 chromosomes ■ ■

■

One of each autosome One X chromosome

One of each autosome One sex determining chromosome (an X or Y)

Haploid cells (cells containing only one copy of the genome)

Chromosomes and Inheritance ■ ■

1 from Mother, 1 from Father Eggs cells contain 23 chromosomes ■ ■

■

Sperm cells contain 23 chromosomes ■ ■

■

One of each autosome One X chromosome

One of each autosome One sex determining chromosome (an X or Y)

Haploid cells (cells containing only one copy of the genome)

DNA (DeoxyriboNucleic Acid) 



String of deoxyribose sugars joined by phosphate groups. Each sugar is attached to one of 4 possible nucleotide bases 

ADENINE (A),



CYTOSINE (C ),



GUANINE (G) or



THYMINE (T)

DNA Double helix structure ■ 2 strands are held together by hydrogen bonds ■ 4 bases pairing rule ■

o o

Adenine = Thymine Guanine = Cytosine

(A = T) (G = C)

DNA Base Pairing

A G C G A T C T G G T C G C T A G A C C Double helix consists of 2 complimentary strands of DNA.

DNA Replication

Semi – conservative replication T

ATC TAG DNA Original double unzips strand

C G

A A T T A A T C G

DNA separates and replicates

ATC TAG ATC TAG 2 new double strands – each containing one parent and one daughter strand

The Genetic Code 

Every three bases of DNA is called a ‘codon’



Each codon specifies an amino acid



Codons specify amino acid sequence of protein

Amino Acid Code •64 possible triplet codons •Only 20 amino acids •Code is “degenerate or redundant” A lanine A rginine A sparagine A sparticA cid Cysteine G lut am ine G lutam icA cid G lycine H istid ine Isoleucine

A la

A

A rg

R

A sn

N

A sp

D

Cys

C

G ln

Q

G lu

E

G ly

G

H is

H

Ile

I

Leucine

Leu

L

Lys

K

M et

M

Ph e

F

Proline

Pro

P

S erine

S er

S

T h r

T

T rp

W

T yr

Y

V al

V

Lysine M eth ionine Ph enylalanine

T h reonine T ryptoph an T yrosine V aline

Codons ATCACCTTCTCCAAGCTCTGA I

T

F

S

K

L

*

DNA Sequence Codons Protein Sequence

Genetic Code U

C

A

G

U UUU UUC UUA UUG UCU UCC UCA UCG UAU UAC UAA UAG UGU UGC UGA UGG

URACIL Phe (F) Phe (F) Leu (L) Leu (L) Ser (S) Ser (S) Ser (S) Ser (S) Tyr [Y] Tyr [Y] Ter [end] Ter [end] Cys [C] Cys [C] Ter [end] Trp [W]

C CUU CUC CUA CUG CCU CCC CCA CCG CAU CAC CAA CAG CGU CGC CGA CGG

CYTOCINE Leu (L) Leu (L) Leu (L) Leu (L) Pro [P] Pro [P] Pro [P] Pro [P] His [H] His [H] Gln [Q] Gln [Q] Arg [R] Arg [R] Arg [R] Arg [R]

A AUU AUC AUA AUG ACU ACC ACA ACG AAU AAC AAA AAG AGU AGC AGA AGG

ADENINE Ile [I] Ile [I] Ile [I] Met [M] Thr [T] Thr [T] Thr [T] Thr [T] Asn [N] Asn [N] Lys [K] Lys [K] Ser [S] Ser [S] Arg [R] Arg [R]

G GUU GUC GUA GUG GCU GCC GCA GCG GAU GAC GAA GAG GGU GGC GGA GGG

GUANINE Val [V] Val [V] Val [V] Val [V] Ala [A] Ala [A] Ala [A] Ala [A] Asp [D] Asp [D] Glu [E] Glu [E] Gly [G] Gly [G] Gly [G] Gly [G]

U C A G U C A G U C A G U C A G

Gene Structure Promoter

Exons AUG start

Introns UAA UAG ‘stop’ UGA

Exon = coding sequence Intron= intervening sequence (non-coding)

Protein Synthesis

Messenger - RNA

DNA Code

Protein Synthesis transcription

DNA

RNA

Protein

translation

Transcription  



Double DNA strands separate DNA sense strand acts as template and is ‘transcribed’ into messenger RNA (mirror image of the DNA but Uracil instead of Thymine) Introns are sliced out of the sequence DNA mRNA

ATCGG UAGCC

Translation  

mRNA leaves the nucleus In the cytoplasm, ribosomes attach to the mRNA ensuring the correct amino acid, for each codon, is added to a growing chain of amino acids which forms the resulting protein.

Transcription

RNA polymerase

exon intron transcription factors

5’

1

2 1

3 2

3’

Transcription

RNA polymerase exon intron transcription factors

5’

1

2 1

3 2

3’

Transcription 5’GGAUUCGUGCUGCUAA

RNA polymerase exon intron

1

2 1

3 2

transcription factors

5’GGATTCGTGCTGCTAA

Transcription

primary transcript

exon transcription factors

intron

1

2 1

3 2

RNA polymerase

Transcription mature mRNA

AAAAAAAAAA

RNA splicing primary transcript

transcription factors

exon intron

promotor

1

2 1

3 2

RNA polymerase

Translation polyadenylation site (AATAAA)

cap structure

5’

AAAAAAAAA

Ribosome

mRNA molecule

cytoplasm

3’

Translation Peptide chain

AAAAAAAAA

5’

Ribosome

mRNA molecule

cytoplasm

3’

splicing

National Human Genome Research Institute (NHGRI)

http://www.nhgri.nih.gov/DIR/VIP/ by artist Darryl Leja

The Human Genome 



Only ~5% of our DNA actually codes for proteins. Little variation exists from person to person.The remainder is ‘junk’ ‘Junk’ DNA includes repetitive sequences such as micro and minisatellites. Varies a lot between individuals allowing ‘DNA fingerprinting’

DNA Replication and Cell Division ■

■

Mitosis ■

One cell produces 2 diploid daughter cells

■

Vital for tissue formation and maintenance

Meiosis ■

One cell produces haploid gametes

■

Vital for reproduction

Cell Cycle

Meiosis In the germ cells, egg and sperm, it is essential there is only one copy of each chromosome pair. The process which results in this is called ‘meiosis’.

Mutations ■

A change in the DNA sequence of the gene Germline mutation (inherited)– present in every cell in the body o Somatic mutation (acquired) – present only in the descendants of that cell o

All cells acquire mutations as they divide ■ Mutations can alter protein product of DNA, stop gene working or activate gene ■

Types of Mutation (in coding sequence)

AGC TTC GAC CCG

Wild type

AGC TGA CCC G Deletion AGC TTC CCG ACC CG Insertion AGC TTC TTC TTC GAC CCG Expansion ATC TGC GAC CCG Point mutation ATC TGA Nonsense ‘stop’

Human Genome ■

Genome structure ■ Chromosome/Gene/DNA

■

Protein Synthesis

■ Transcription

■

DNA Replication /Cell Division ■ Mitosis

■

and Translation

Mutations

and Meiosis

THE END