Gene to proteinThe two main processes that link the gene to

protein are: RNA transcription and translation.

The bridge between DNA and protein synthesis is RNA.

The specific sequence of the nucleotides in each gene carries the information for the primary structure of a protein which is the linear order of the 20 possible amino acids.

The link between genes & proteinsDNA uses RNA to create proteins. In other words, genes provides the basic instructions to make proteins. Thus, proteins are the links

between genotype (genes) and phenotype (the way we look).The sequence of nucleotides in DNA is connected with 20 amino acids, therefore, different proteins are created based of type of

DNA .

Inside the nucleus In the cytoplasmEukaryotic cells

Prokaryotic cells

In the cytoplasmIn the cytoplasm

During the RNA transcription , a DNA strand provides a template for the synthesis of a complementary RNA strand. Which actually produces a messenger RNA called mRNA.

During the RNA translation that occurs in the ribosomes the information is in the sequence of the nucleotides in the mRNA which is used to determine the amino acid sequence of a polypeptide.

The basic mechanics of the transcription and the translation are similar in both eukaryotic and prokaryotic cells.

.

In a prokaryote, because the bacteria has no nuclei the two mechanics are coupled and the ribosomes attach to the leading end of the mRNA while the transcription is still in process.

In an eukaryotic cell the transcription happens in the nucleus and the translation mainly occurs in the ribosomes in the cytoplasm.

There is a molecular command chain in a cell which is :

DNA mRNA Protein Transcription translation

In nucleotides, every 3 nitrogenous bases give one amino acid. The triplet is called codon, and every amino acid may

be represented by one or more codons.

There are special codons that interact with translation process

Codon in where the process starts AUG

Codons in where the process stops

UAAUGAUAG

1 .RThe RNA polymerase separates the DNA strands at a suitable point and

bonds the RNA nucleotides along the DNA template.

RNA polymerase can only add nucleotides to the 3rd end of the

growing polymer just like the DNA polymerase.

There are specific points that are marked on the DNA that show when the

transcription begins and ends.In prokaryotes the bacteria has only

one RNA polymerase. But in eukaryotes it has three RNA polymerase (I, III, II, and , and

IIIIII) RNA polymerase 2 is used to synthesis ) RNA polymerase 2 is used to synthesis mRNAmRNA..

NA polymerase separates the two strands of DNA

2 .One of the two DNA strands become the template.

4 .RNA nucleotides are bonded to the template by RNA polymerase. The codons along the DNA template are read from 5~>3 as RNA nucleotides are added from the 3’ end.

5 .RNA nucleotides addition is based on the base-pair rules (U with A) until it

reaches the terminator .

3 .A promoter indicates the starting point and has a binding site for RNA polymerase.

NOTE THAT

ProkaryotesEukaryotes

One RNA polymerase

3 types RNA polymerase (RNA polymerase II is

used to synthase mRNA )

6 .pre-mRNA is created & ready to be modified.

Two things are added to the pre-mRNA to give mRNA that is ready to leave the nucleus.

It is a modified form of guanine (G) that function as:1.Protection from hydrolytic enzymes.2.A start point for the translation.

50 to 250 adenine (A) are added to form poly(A) tail that facilitates the export of mRNA from the nucleus.

CUU

The amino acid that goes with the triplet base at mRNA

Anticodon base-pair with the complementary codon at mRNA

The growing end of the polypeptide chain

It’s transcribed in the nucleus and has 3 functions:1.Pick up its relevant amino acid.2.Deposit the amino acid at the ribosomes.3.Return to cytosol to pick up another amino acid

The tRNA molecules are transcribed from DNA in the nucleus once it reached the cytoplasm

each tRNA is used for 3 functions:.1Pick up specific amino acids from the

cytoplasm.2Deposit the amino acid in the ribosome .3Return to the cytoplasm and pick another

copy of the same amino acid.The anticodons on some of the tRNA’s

recognize more than one codon.

RibosomesEach ribosome has a large subunit and a

small subunit which is formed in the nucleolus.

They facilitate the coupling of tRNA anticodons with mRNA codons.

They are composed of proteins and ribosomal RNA (rRNA) which is the most abundant RNA in the cell.

rRNA is transcribed in the nucleus, then it goes to the nucleolus where it binds with ribosomal subunits. The subunits exit the nucleolus to the cytosol and they join to form ribosomes with

mRNA attaches to them,

Ribosomes have:1. One binding site for mRNA2. Tree binding sites for tRNA

a. P site: tRNA with the growing polypeptideb. A site: next tRNAc. E site: exit port for tRNA to leave.

Multiple ribosomes may trail along the same mRNA, so it can be used to make many copies od polypeptide at the same time.

Translation has three stages

• mRNA attaches to its site.

• tRNA attaches to A site with the first amino acid (anticodon that binds with mRNA codon)

• Subunits are joined & tRNA is at P site.

• One of the 3 stop codon accurse at A site. (UAG,UAA,UGA)

• A release factor binds with the stop codon.

• The bond between the polypeptide & tRNA is hydrolyzes.

• This frees the polypeptide and the translation complex disassembles.

Hydrogen bonding is formed between mRNA codon & anticodon by elongation

factors.

1 .Codon recognition

With the help of rRNA molecule, the polypeptide chain in P site is separated from tRNA and moved to A

site, it binds with a new amino acid carried by new

tRNA.

2 .Peptide bond formation

Ribosomes move the new tRNA in A site to P site.

3 .Translocation of tRNA

polyribosomesA ribosome requires less than a minute to

translate an average-sized mRNA into a polypeptide

A single mRNA is used to make many copies of a polypeptide simultaneously.

Mutations are the changes in the genetic material of a cell or a virus. There are different kinds of mutations, but we are going to study the

point mutation.

Is the chemical change in only 1 base pair. It may be transmitted to the offspring it happened in cells producing gametes. Types:

• X-ray• Ultraviolet

light

• Base analogues• Distorting double helix• Change the pairing properties

Point mutationBase-pair substitution Insertion and deletion

Silent mutation

It’s the switch of one amino acid to another with similar properties

(have no or little impact) Missense mutationThe change in amino acid that

leads to another protein.

Nonsense mutation

Change the amino acid codon to stop codon. This leads to nonfunctional protein.

The mutation in which additions or losses of nucleotides. This will make the codon group improperly.

This type have a disastrous effect on the

resulting protein.And will end in

nonsense premature termination

Mutagens These are chemical or physical agents that

interact with DNA to cause mutations1.Physical agents: high energy radiation like X-

rays and UV light2.Chemical agents: some mutagens cause

chemical changes in the bases that change their pairing properties – others interfere with the replication of the DNA by inserting and distorting the double helix

Point mutation and insertions and deletions

DNA MUTATION

http://www.youtube.com/watch?v=kp0esidDr-c

PLZ,OPEN THE VIDEO

From Gene to Protien.3gp

Protein Synthesis

http://www.youtube.com/watch?v=w8FSDQwumTw

Protein Synthesis Animation Video

http://www.youtube.com/watch?v=Ikq9AcBcohA

Translation Animation

http://www.youtube.com/watch?v=ZPlnDzkBrpc

 Q1: Write whether each of the following

statements is True (T) or False (F): 1-tRNA carries encoded genetic message from DNA in

the nucleus to the ribosomes in the cytoplasm.2-Missense mutations change an amino acid codon

into a stop codon, nearly always leading to a nonfunctional protein..

3-The promoter of a gene is a region at which RNA polymerase attaches and initiate transcription.

 4-A genetic codon may code for more than one amino acid.5- During translation ,AUG is a start codon while UAA is a

stop codon.

Q 2: Choose the correct answer (one answer only):  1-In eukaryotic cells ,transcription of RNA occurs in the;- a-Cytoplasm. b-Nucleus. c-Ribosomes. 2. What is the proper order of the following events in the expression of a eukaryotic gene?

1. translation2. RNA processing3. transcription4. modification of protein

1, 2, 3, 4 3, 2, 1, 4 4, 2, 3,1 2 ,3, 4, 1 3- Translation occurs in the _____.  cytoplasm lysosome nucleus mitochondrion 4 .During RNA processing a(n) _____ is added to the 5' end of the RNA.    3' untranslated region a long string of adenine nucleotides 5' untranslated region modified guanine nucleotide 5- .Which one of the following statements is true?   Each DNA base codes for three amino acids. Each gene codes for three proteins. It takes three genes to code for one protein. Each amino acid in a protein is coded for by three bases in the DNA.

6-The function of tRNA during protein synthesis is to _____.   deliver amino acids to their proper site during protein synthesis attach mRNA to the small subunit of the ribosome process mRNA transcribe mRNA 7- The P site of a ribosome does which one of the following?  It holds the tRNA that is carrying the next amino acid to be added to the growing polypeptide chain. It holds the growing polypeptide chain. It catalyzes the addition of amino acids to the tRNAs. It recognizes the promoter during transcription initiation. 8-   During translation, amino acid chain elongation occurs until _____.   no further amino acids are needed by the cell all tRNAs are empty the polypeptide is long enough the ribosome encounters a "stop" codon 9- A geneticist found that a particular mutation had no effect on the polypeptide encoded by the gene.

This mutation probably involved _____.   deletion of one nucleotide insertion of one nucleotide a nonsense mutation a silent mutation   10 . A point mutation in which a single base pair is inserted or deleted from DNA is called a(n) _____. nonsense mutation frame-shift mutation inversion mutation translocation mutation