Unit 1.3 Gene expression Flashcards
What is meant by the genotype of an organism?
The genetic material that an organism possesses. The genotype of an organism is determined by the sequence of bases in the organisms chromosomes.
What is meant by the phenotype of an organism?
The physical appearance of an organism. A cell’s phenotype is determined by the proteins that are produced as a result of gene expression
State the differences between DNA and RNA molecules?
- DNA molecules can be found in the nucleus, whereas RNA molecules can be found in both the cytoplasm and the nucleus of the cell.
- There is only one type of DNA, however there are three types of RNA
- DNA is a double stranded molecule, whereas RNA is a single stranded molecule.
- The sugar present in the nucleotides of DNA molecules is deoxyribose, whereas the sugar present in the RNA nucleotides is Ribose sugar.
- In a DNA nucleotide the base adenine will be paired with thymine, however RNA molecules do not contain the base thymine and instead contain the base uracil.
What are the different types of RNA?
- mRNA, messenger RNA copies the code from the DNA molecule and carries it out to the ribosomes where proteins can be synthesised.
- tRNA, transfer RNA becomes attached to a specific amino acid and will transport this specific amino acid to the ribosome to be synthesised into a polypeptide chain
-rRNA, ribosomal RNA, a type of RNA that is bound to structural proteins that forms the ribosomes.
What is a promoter region?
a region where transcription is initiated
What happens during the first stage of Transcription?
The enzyme RNA polymerase moves along the gene, it will unzip and unwind the DNA strands when the hydrogen bonds between DNA bases break. This exposes a single template strand of DNA.
What happens during the second stage of transcription?
Free RNA nucleotides in the nucleus bind to complementary DNA nucleotides using the rules of base pairing. The RNA nucleotides are held in place by hydrogen bonds while strong covalent bonds from between the phosphate of one nucleotide and the ribose sugar of the next. This is all facilitated by the enzyme RNA polymerase which can only add RNA nucleotides in a 5’ to 3’ direction.
What is the final stage of transcription?
The mRNA stand will continue to elongate until a terminator sequence of nucleotides on the DNA strand is reached. When this terminator sequence is reached transcription is complete and the RNA polymerase enzyme and the mRNA molecule that has been constructed will be released.
What is the product of the Transcription stage of gene expression?
The primary mRNA transcript.
What happens during RNA splicing?
The primary mRNA transcript is made up of:
- Non-coding regions called introns which are removed from the primary mRNA transcript
- coding regions called exons that are retained and joined together to form the mature mRNA transcript.
It is important to note that the order of the exons remains unchanged before and after RNA splicing
What is meant by Alternative RNA splicing?
This is the process by which different proteins can be expressed from one gene (gene expression), this is because different mature mRNA transcripts can be produced dependant on the order in which exons have been retained.
What do we call the second stage of gene expression?
Translation
What role do tRNA molecules play in translation?
- tRNA have a particular triplet of bases exposed called an anti-CODON, the tRNA anti-CODON is complementary to the CODON of the mature mRNA transcript. tRNA also has an attachment site for a specific amino acid, this way a specific amino acid can be transported to the ribosome by the tRNA.
Describe the process of translation?
the mature mRNA transcript travels through the cyptoplasm to the ribosome to which it attaches itself. The ribosome has binding sites for 2 codons, tRNa molecules transport specific amino acids to the ribosome each mRNA codon codes for a specific amino acid. The first codon is known as a start codon as it begins the process of translation. The anti-codon of the tRNA and the codon of the mRNA bind together temporarily by weak hydorgen bonding, and strong peptide bonds then begin to form between the amino acids coded for by the mature mRNA transcript. the used tRNA molecules will then leave the ribosome and collect another specific amino acid. The last codon in the mature mRNA transcript will be the stop codon and this codon indicates that the translation process has concluded.
What bonds join amino acids together?
Strong peptide bonds
