Topic 2:7 - genes and protein synthesis Flashcards
(20 cards)
What is a gene?
A gene consists of a unique sequence of nucleotides that code for a functional protein or an RNA molecule.
What two components do genes contain?
introns and exons.
Introns are DNA sequences that do not directly code for proteins and occur between the exons of a gene.
Exons are DNA sequences that code for protein.
Define protein synthesis
Protein synthesis involves transcription of a gene into messenger RNA (mRNA), and translation of mRNA into an amino acid sequence at the ribosomes.
Where does transcription occur?
In eukaryotic cells, transcription occurs in the nucleus.
where does translation occur?
in the cytoplasm
Where does mRNA splicing/ processing of immature mRNA occur?
In eukaryotic cells, this occurs in the nucleus.
What is RNA, explain its structure, and the importance of its shape
RNA is single stranded but folding to produce unique shape needed for function will occur. Folding will happen because it is single strand (with exposed bases) and the complementary bases will attract
Explain why there is a binding site on RNA
energy is needed to bind amino acid to tRNA therefore a binding site for ATP and amino acid is needed.
What are the two stages of protein synthesis?
transcription and translation
What is transcription?
Where a strand of mRNA is synthesised from a specific gene or segment of DNA. This will be translated to synthesise an polypeptide.
Explain the process of transcription
- In the nucleus RNA polymerase unwinds a section of DNA and the two strands separate to expose the bases of a gene.
- Free RNA nucleotides complementary bind to the exposed bases i.e. A-U, G-C
- The enzyme RNA-polymerase checks the sequence of bases and joins the RNA nucleotides together forming the sugar-phosphate backbone of the mRNA.
- Single-stranded mRNA detaches from the DNA strand.
what does RNA use instead of thymine and why?
uracil replaces thymine in RNA as it is energetically less expensive than thymine
What are the two separated DNA strands called during transcription?
The DNA strand which is used to produce the pre-mRNA molecule is called the template strand
the other strand is termed the complementary/coding strand. (due to the fact the coding strand is the DNA strand whose base sequence is identical to the base sequence of the RNA transcript produced).
What happens right after transcription?
This long chain of newly formed mRNA contains introns and exons and is known as ‘immature’ mRNA. The introns (non-coding regions) are cut out (by enzymes) and the exons are spliced together to make a shorter piece of ‘mature’ mRNA that carries the code for a polypeptide. This is called RNA splicing and it occurs in the nucleus
What is a codon, what do they do, and what is it specified by?
In mRNA each triplet of bases is called a codon and each codes for one amino acid (or stop signal) in the synthesis of a protein molecule.
mRNA codons are specified by the order of bases in the gene on the template strand of DNA.
what happens after the exons have been spliced to create ‘mature’ mRNA
‘Mature’ mRNA leaves the nucleus via nuclear pores and attaches to a ribosome in the cytoplasm of the cell.
What are tRNA molecules and what do they do?
transfer RNA molecules are single stranded RNA molecules which have a specific clover leaf shape due to the attractions between its exposed bases. They are found in the cytoplasm and are responsible for carrying one specific amino acid to the ribosome.
What is an amino acid and how are the sourced for protein synthesis?
Amino acids are the building blocks of proteins. The amino acid carried is specified by the anticodon on the tRNA molecule
Describe the process of translation
- tRNA molecules bond to their specific amino acid that coincides with the specific codon complementary to the anticodon on the tRNA molecule.
- the tRNA carries its amino acid to the ribosome, where the mRNA strand is.
- at the ribosome, the tRNA’s are positioned correctly by complementary base-pairing (hydrogen bonds) between the anticodon on the tRNA and the codon on the mRNA.
- a peptide bond is formed between the first two amino acids, and the first tRN is released, leaving its Mino acid behind.
- The ribosome moves along the mRNA allowing another tRNA to base-pair and position the next amino acid for a peptide bond to form.
- more peptide bonds form between more amino acids, until a stop codon is reached and the polypeptide chain is released and folds into its 3D shape, hence a protein is made.
If RNA is always synthesised from what direction? Hence, which strand will it transcribe?
5’ to 3’, hence it will transcribe the DNA strand that runs from 3’ to 5’, because the two strands need to be antiparallel.
