DNA STRUCTURE 3.3.3page 63-74

• Basic units are nucleotide• Nucleotides are made of C,H,O,N,P

Where is DNA found in a prokaryotic cell? In eukaryotic cell

STRUCTURE OF NUCLEIC ACIDS

• There are two types of nucleic acids, RNA and DNA.

• Both of them are made of long chains (polymer) of nucleotides.

Polynucleotide 3.3.3

Structure of nucleotide 3.3.1

Types of nucleotides 3.3.2

Nucleotides come together by dehydration (condensation) synthesis for RNA or DNA.

Chemical bond between nucleotides is called phosphodiester bond.

Nucleoside

phosphate

ribose

Nitrogeneous base

In the formation of double helix adenine always bind with thymine, guanine always bind with cytosine.

Two DNA strands are held together by weak hydrogen bonds.

(that means they can be seperated easily)

There are 2 H bonds between Adenine and Thymine. 3 H bonds between Guanine and Cytosine.

Double helix

DNA (deoxyribonucleic acid)

• Functions of the DNA:

• Carry genetic information from parent to offsprings.

• Control protein synthesis in the cell.

3.4. Replication of DNA

1- Two strands are seperated from each other by an enzyme called helicase.2- Replication takes place on both strands.3- Old starnds are used as templates.4- DNA polymerase adds nucleotides to form two new strands

* This process is called semi-conservative replication. Why?

DNA replication 3.4

3.4

3.5 Ribonucleic acid• 5 carbon sugar is ribose.• Nitrogenous bases are

A,G,C,Uracil• There are three types of

RNA• -mRNA• -rRNA• -tRNA

3.5 Nitregenous bases

mRNA (messenger RNA): carries genetic information from DNA to ribosome. It encodes aminoacid sequence of a polypeptide

(protein). It is single strand.tRNA (transfer RNA): interprets language of mRNA into amino acid language. tRNA recognizes codons of mRNA and transfer aminoacid which is coded by codon.

rRNA (ribosamal RNA): it is found in the subunits of ribosome. The most abundant RNA.

3.5 Transcription, translation

3.5 How does DNA control cellular activities?

• How does Mr.Du Rand control school activities?• There are intermediate administrators (dean, department

heads)

The genetic information is used to synthesize proteins which carry out cellular activities.

DNA determines the aminoacid sequence of proteins.

• How does the information in DNA lead to the synthesis of specific proteins? How is the information in DNA transported from the nucleus to the cytoplasm?

Language of life

• There are 4 letters in the language of DNA (A,G,T,C)

• Three letters form a word such as AAA, GTA ….. There are 64 different words in this language.These triplet nucleotides (words) are called genetic code.

• 61 genetic codes code amino acids, 3 of them do not code.

Transcription:

- The transfer of genetic information from DNA to RNA. It is like replication of DNA.

- Two strands of DNA are seperated from each other.- RNA polymerase adds RNA nucleotides by using DNA strand

as template. Adenine pairs with uracil, guanine pairs with cytosine.

- When transcription is completed mRNA leaves the nucleus and DNA strands form double helix structure again.

Language of RNA

• mRNA takes genetic information from DNA by transcription.

• The letters of RNA are A, G, C, U. Three letters form a codon which codes an amino acid.

• There are 64 different codons, only 61 code amino acids, 3 of them do not code amino acid.

DNA has AAGTCGCTCACC sequence

mRNA has UUCAGCGAGUGG sequence

There are 64 different codons on mRNA.What is the amino acid sequence of a polypeptidewhich is produced from thismRNA?phe-ser-glu-trp

TranslationIs the process in which protein is synthesized according to genetic information on mRNA.

It takes place in the ribosome.

tRNA molecules transfer amino acids according to codon anti-codon recognition.

3.5.5. One gene-one enzymepage 71-74

In the past it is believed that each gene codes an enzyme. This hypothesis is called one gene-one enzyme.After further researches, one gene one enzyme hypothesis is modified as one gene one polypeptide

Each gene works by coding for the synthesis of one particular protein, such as an enzyme.

Questions:

• A DNA strand has AAGTCCGCTTAA nucleotide sequence.1- What will be nucleotide sequence of the complementary

strand of this DNA strand?2- What will be nucleotide sequence of the mRNA which is

transcribed from this DNA strand?3- What would happen to the DNA strand after transcription?