1.3 Control of Gene Expression Flashcards
What is ‘gene expression’?
Process that results in the production of a protein
How does gene expression control the phenotype of an organism?
Gene expression = codes for protein which determine an organism’s phenotype
How is gene expression controlled?
Regulation of transcription and translation
What factors can influence gene expression?
Intracellular and Environmental factors
Only a fraction of genes are expressed. Explain this statement in relation to specialised cells.
Genes can be switched on and off. It they are switched on, they are expressed and produce proteins.
Each specialised cell will only switch on the genes that code for proteins characteristic of that cell .
What is the key enzyme in Transcription?
RNA Polymerase
Where does transcription take place?
Nucleus
Why can’t a full copy of the DNA go to the ribosome?
DNA is too big to leave the nucleus through the nuclear pores
What are the key requirements for Transcription?
- RNA Polymerase
- free mRNA bases
- DNA Template
Describe the key steps in the process of transcription
- RNA polymerase moves along DNA unwinding the double helix.
- RNA polymerase also breaks the weak hydrogen bonds between bases, separating the two DNA strands
- Free RNA nucleotides pair with their complementary base pair on the template strand. Weak hydrogen bonds form between complementary bases.
- Strong chemical bonds form between the sugar and phosphate of neighbouring nucleotides (bond formation catalysed by RNA polymerase).
- The strand of messenger RNA made by the RNA polymerase is known as the primary transcript
What are the coding regions in an mRNA strand called?
Exons
What are the four forms of nucleic acid?
- mRNA
- tRNA
- rRNA
- DNA
Describe the process of mRNA splicing
A primary transcript has the introns cut out of them and the exons combined to form a mature transcript
Where does mRNA splicing take place?
Nucleus
What is the function of mRNA?
Carry a copy of the genetic material from the nucleus to the ribosome to be translated
What is the function of tRNA?
Carries specific amino acids to the ribosome to convert mRNA to a polypeptide chain
What is the function of rRNA?
Combines with protein to form a ribosome
Describe the structure of a tRNA molecule
Amino acid attachment site - specific AA that pairs up with anticodon attaches
Anticodon attachment site - triplet of bases that are complementary to codon on mRNA strand
State the name of the sugar molecule present in RNA
Ribose Sugar
Where does translation occur?
Ribosome
What is translation?
Synthesis of protein from a mature mRNA template
Describe the steps in translation?
- mRNA enters the ribosome, start codon initiates translation
- tRNA molecules come along that have an anticodon complementary to the codon of the mRNA
- tRNA molecules drop off the amino acid they are carrying
- A polypeptide chain forms as the tRNA molecules keep dropping off the AA
- When the stop codon is reached no more amino acids are added to the polypeptide chain and translation finishes.
What type of bond forms between adjacent amino acids?
Peptide
How do tRNA molecules ensure the correct sequence of amino acids?
tRNA drop off their amino acid when the anticodon is complementary to the mRNA codon being translated, the tRNA anticodon will line up with its complementary mRNA codon
What is a codon?
A triplet of bases on the mRNA strand that are complementary to an anticodon the tRNA molecule
What is a start codon and where is it found?
A triplet of bases that initiates translation found at the start of the mRNA strand
How can a different protein be expressed from one gene?
Alternative RNA Splicing
How can alternative RNA splicing alter the final protein?
Different combinations of EXONS are left in the mature transcript. Exons can be treated as introns and removed.
Describe how the 3D structure of a protein is formed
Primary structure of protein consists of amino acids linked by peptide bonds forming polypeptide chain
Secondary structure of protein is formed by polypeptide folding and being held together by hydrogen bonds and other interactions.
Give an example of a protein in the body and its function
Enzymes - speed up chemical reactions by lowering activation energy
Hormones - chemical messengers that travel in bloodstream to target organs to bring around a response
Antigenic Proteins - signature proteins that identify to an immune system if a cell belongs to an organism
What is a function of a non-coding sequence?
Regulation of transcription
DNA and RNA are different. RNA has … strand, … instead of … and a … sugar instead of a … sugar.
one strand … uracil instead of a thymine … ribose sugar instead of a deoxyribose sugar. DNA and RNA are different. RNA has one strand, uracil instead of a thymine and a ribose sugar instead of a deoxyribose sugar.
