3.4.2 DNA and protein synthesis Flashcards
Define genome
complete set of genes in the cell
Define proteome
The full range of proteins that a cell can make
Define codon
Three bases on mRNA that code for an amino acid
Define anti-codon
Three bases on tRNA that are complementary to the codon on mRNA
Name the process that removes base sequences from pre-mRNA to form mRNA.
Splicing
Give some ways in which the structure of an mRNA molecule is different from the structure of a tRNA molecule.
- mRNA is a single helix where as tRNA is a clover shaped molecule
- mRNA do not contain hydrogen bond where as tRNA do
- mRNA do not have base pairing where as tRNA do
- mRNA has codons where as tRNA has anti-codons
- mRNA don’t have an amino acid binding site where as tRNA do
Explain the difference between pre-mRNA and mRNA.
- Pre-mRNA contains introns where as mRNA contains only exons;
- mRNA has undergone splicing, pre-mRNA has not.
What is the role of RNA polymerase during transcription?
To join RNA nucleotides together (by forming phosphodiester bonds) to form mRNA
Name the three steps involved in protein synthesis
Transcription
Splicing
Translation
Describe how mRNA is produced in the nucleus of a cell.
- DNA helicase breaks the hydrogen bonds holding complementary base pairs
- One DNA strand acts as a template
- Free RNA nucleotides are attracted to DNA template strand.
- RNA nucleotides bind to their complementary base pair on the template strand - A>U; C>G
- RNA polymerase joins RNA nucleotides together
- Pre-mRNA is spliced to remove the introns
Explain the role of the anticodon in protein synthesis.
Anticodons on the tRNA bind to codons on the mRNA
Anticodons are complementary to those on the codon
So the correct amino acid is brought to the ribosome
Name the organelle involved in translation.
Ribosomes
Describe the role of tRNA in the process of translation.
- Anticodons on tRNA are complementary to specific codons on mRNA
- A specific amino acid is bound to the tRNA
- This amino acid is carried to the ribosome
- Ribosome moves along mRNA.
- Peptide bond forms between adjacent amino acids.
- Via condensation reaction
- Requires ATP.
- Ribosome detaches from mRNA when STOP codon reached.
Starting with mRNA, describe how the process of translation leads to the production of a polypeptide.
- The mRNA attaches to a ribosome
- Anticodons on tRNA are complementary to specific 3. codons on mRNA
- A specific amino acid is bound to the tRNA
- This amino acid is carried to the ribosome
- Ribosome moves along mRNA.
- Peptide bond forms between adjacent amino acids.
- Via condensation reaction
- Requires ATP.
- Ribosome detaches from mRNA when STOP codon reached.
What is a histone?
A protein that DNA forms a complex with to allow it to be condensed into a chromosome.
When chromosomes become visible at the start of cell division, they appear as 2 threads joined at a central point called a…
centromere
The 2 condensed ‘threads’ of DNA that are joined at a centromere and make up a chromosome are called…
sister chromatids
Describe how DNA is packed into a chromosome.
- DNA molecule combines with histones.
- DNA-Histone complex begins to coil and fold to form loops.
- Loops coil further and pack together to form the chromosome.
What is meant by homologous chromosomes?
- A pair of corresponding maternal and paternal chromosomes.
- Their genes (are the same) are at the same loci so they determine the same characteristics.
The total number of maternal AND paternal chromosomes in an organism is called its…
diploid number
If a tRNA is involved what stage of protein synthesis are we looking at?
translation
what shape does a tRNA have?
clover shape
The codon on mRNA is AUG - what will be the complementary DNA and anti-codon?
DNA - TAC
anti-codon - UAC
How do new alleles come about?
- Random mutations alter coding sequences.
- This leads to changes in the amino acid sequence.
- This leads to a different polypeptide with a possibly different function/non-functional.
Do homologous chromosomes carry the same alleles (version of genes)?
No - they do carry same genes
Define allele.
A version of a gene e.g. blue and brown versions of the eye colour gene.
How do new alleles come about?
- Random mutations alter coding sequences.
- This leads to changes in the amino acid sequence.
- This leads to a different polypeptide with a possibly different function/non-functional.
How are DNA nucleotides different to RNA nucleotides?
DNA has thymine RNA has uracil
DNA has deoxyribose RNA has ribose
How is mRNA structure different to tRNA?
mRNA longer
mRNA straight - tRNA clover shape
mRNA has no paired bases/no hydrogen bonds
Describe how mRNA is made in the nucleus
- Helicase;
- Breaks hydrogen bonds;
- Only one DNA strand acts as template;
- RNA nucleotides attracted to exposed bases;
- (Attraction) according to complemtary base pairing rule (AU, GC, TA, CG);
- RNA polymerase joins (RNA) nucleotides together;
- Pre-mRNA formed and is spliced to remove introns
- forming mRNA;
name the 3 bases in mRNA that codes for a specific amino acid
codon
Describe the role of the ribosome in the production of a polypeptide
mRNA binds to ribosome
two codon binding sites
tRNA with specific anticodon bind to codon
formation of a peptide bond in ribosome between amino acids
ribosome moves along mRNA
The base sequence of mRNA maybe different the sequence of pre-mRNA in eukaryotic cells
introns in pre mRNA
splicing removes these introns
so only exons present in mRNA
define degenerate
more than one codon codes for a single amino acid
describe how mRNA differs to tRNA
- mRNA has no H bonds tRNA does
- mRNA has codon, tRNA has anticodon
- mRNA is longer
- mRNA linear, tRNA clover shaped
- mRNA has no AA binding site, tRNA does
Describe translation
- mRNA binds to ribosome
- ribosomes moves to START codon (AUG)
- 2 codons fit in the ribosome
- first tRNA enters carrying specific AA
- anticodon binds to mRNA codon
- second tRNA enters - 2 tRNA binding sites
- AA join by peptide bond using ATP
- ribosome moves along to next codon to read
