Gene expression!!

What is gene expression?

The process by which specific genes are activated to produce a required protein

What does gene expression involve?

The transcription and translation of DNA sequences

Only a _______ of the gene in a cell are _______?

• Fraction

• Expressed

The primary structure of a protein is determined by…?

The sequence of nucleotide bases in a DNA strand which cannot leave the nucleus

The genetic code must be ….? How is it possible?

• Copied, carried outside the nucleus and translated into protein on the ribosome

• Because of three different types of RNA

Transcription and translation involve 3 types of RNA, which are?

• mRNA

• tRNA

• rRNA

What bases are in a RNA nucleotide?

Uracil, Adenine, Cytosine and Guanine

What is the function of messenger RNA?

carries a copy of the genetic code from the nucleus to the ribosomes

What happens to messenger RNA?

mRNA is transcribed from DNA and the nucleus and translated into proteins by ribosomes in the cytoplasm

What is a codon and its function?

A triplet of bases on the mRNA molecule and it codes for a specific amino acid

What is the function of transfer RNA?

each tRNA molecule carries it’s specific amino acid to the ribosome

What does a tRNA molecule have?

an anticodon at one end and an attachment site for a specific amino acid at the other end

What is an anticodon?

An exposed triplet of bases

rRNA and proteins form?

The ribosome

What does a RNA nucleotide contain?

Phosphate, ribose sugar and a base

RNA molecules are ______ stranded?

Single

The first stage of protein synthesis take place in the _____ and is called ________?

• Nucleus

• Transcription

The production of mRNA is _______.

Essential

Why is the production of mRNA essential?

Because DNA is too large to pass through the nuclear membrane

What is a primary mRNA transcript?

Molecule made when DNA is transcribed

What is RNA polymerase?

Enzyme involved in synthesis of primary transcripts from DNA

Stages of Transcription?

1. RNA polymerase moves along the DNA unwinding the strand.

2. Hydrogen bonds between base pairs break

3. As RNA polymerase breaks the bonds, it synthesises a primary transcript of mRNA using RNA nucleotides. These form hydrogen bonds with the exposed DNA strand by complementary base pairing.

4. The primary transcript of mRNA is processed to produce a mature transcript of mRNA.

5. The mature mRNA transcript is now ready to leave the nucleus and travel to the ribosome.

What is involved in the translation of mRNA into a polypeptide at a ribosome?

tRNA

Where does translation begin and end?

At a start codon and a stop codon

Stages of translation?

1. The mRNA molecule travels through the cytoplasm and attaches to the ribosome.

2. tRNA molecules transport specific amino acids to the ribosome.

3. Each mRNA codon codes for a specific amino acid.

4. The first codon of an mRNA molecule is a start codon. This signals the beginning of translation.

5. The anti-codons and codons match up and form complementary base pairs.

6. Peptide bonds form between the adjacent amino acids to form the polypeptide (protein).

7. Used tRNA molecules exit the ribosome and collect another specific amino acid.

8. The last codon of an mRNA molecule is a stop codon which signals the end of translation.

What can happen after translation?

the polypeptide chain can be changed by cutting and combining polypeptide chains or by adding phosphate or carbohydrate groups to the protein.

What is RNA splicing?

joining of exons following the removal of introns from a primary transcript

What does RNA splicing form?

A mature mRNA transcript

What are introns?

Non-coding regions of the primary transcript that are removed

What are exons?

Coding regions that are joined together to form the mature transcript

The order of exons is …?

Unchanged during splicing

Different proteins can be expressed from ________ as a result of what?

• One gene

• RNA splicing

Different ________ are produced from the same primary transcript depending on what?

• Mature mRNA transcripts

• Which exons are retained

Amino acids are linked by _____ to form what?

• Peptide bonds

• Polypeptides

Polypeptide chains fold to form ….?

The three-dimensional shape of a protein, held together by hydrogen bonds and other interactions between individual amino acids.

Proteins have a large variety of ______ which determines their _______.

• Shapes

• Function

What also influences phenotype?

Environmental factors