Topic 8: DNA, Genes, Protein Synthesis Flashcards
What is a gene
A gene is a base sequence of DNA that codes for:
- the amino acid sequence of a polypeptide
- a functional RNA
What do you call the fixed position of the gene on a DNA molecule
Locus
Where is DNA found
Mostly in nucleus
(also in mitochondria as mitochondial dna)
What are the 4 bases of DNA
- Adenine
- Thymine
- Cytosine
- Guanine
What is a codon
A sequence of three bases that codes for a single amino acid
How many amino acids are coded for in protein synthesis
20 amino acids
(because some have multiple codes)
What does it meanby the genetic code being degenerate
several code words have the same meaning (amino acid)
What are stop codes
When the codon does not code for an amino acid, but for the ribosome to stop the polypepetide chain
What is always the start codon
Methionine
(AUG)
What does it mean by the code is non-overlapping
Each base is only read once, and the triplets are read in the same direction
What does it mean by the code being universal
The genetic code is the same in almost every living being, with a few specific exceptions.
What do you call a sequence that does not code for an amino acid
Introns
What do you call a sequence that codes for an amino acid
Exons
What happens to the introns
They are removed by splicing before the final mRNA reach the ribosomes.
What do you call the proteins associated with DNS
Histones
What forms a chromosone
DNA molecule and its associated proteins (histones)
When the cell is not dividing, what are the chromosones like?
- not visible
- uncoiled
- loosely found throughout nucleus
How do chromosones appear at the start of cell division
Two threads joined at a central point (centromere).
What does each chromosone consist of
- two identical DNA molecules (chromatids)
- held together by proteins called histones.
How are chromatids of a chromosone produced?
- The DNA helix is wound tightly around histones acting as packaging proteins, forming a nucleosome.
- A series of nucleososmes looks like beads on a string in an electron micrograph.
- The string of nucleosomes then loops and coils into the *30nm fibre. *
- The 30nm fibre folds up further into a 300nm wide supercoil.
- This then produce the chromatid of a chromosome.
What is the advantage of DNA coiling?
A lot of DNA can be packed into the chromosome, with each chromosome consisting of a single, very long strand of DNA.
What is a homologous pair
- two copies of each chromosome
- always carry same genes but may have different alleles of the genes.
During meiosis, what happens to the number of chromosones
number of chromosomes is halved and this is controlled so that each daughter cell end up with one chromosome from each homologous pair.
What is an allele
One of a number of different forms of the same gene.
How do you inherit alleles (sexual organisms)
- One allele from mum
- One allele from dad
(Can be different or the same)
What happens if the two inherited alleles are different
The result will be two different polypeptides being expressed.
What happens to the allele if there is a mutation
A new allele will form, producing a different polypeptide
What is an organisms genome
The complete set of genes in a cell, including those in mitochondria and chloroplasts.
What is the proteome
The full range of proteins produced by the genome
Where does the synthesis of proteins happen?
In the cytoplasm
(in the ribosomes)
What is the function of mRNA
To transfer information from the nucleus to the ribosome
Name four differences between RNA and DNA
- RNA has the sugar ribose instead of deoxyribose
- RNA has the base uracil instead of thymine
- RNA is usually single stranded, but can fold into 3-dimentional structures, like proteins.
- RNA is usually shorter than DNA
How long is mRNA
One gene long
How does the codon bind to a tRNA molecule
Using the anticodon of the tRNA
What are some features of a tRNA molecule
- One end has the amino acid bidning site
- One end has the anticodon which is a triplet code to bind to the codon
- Clover shaped
How are the amino acids attatched to the tRNA molecule
By specific **aminoacyl tRNA synthase enzymes. **
What two things form ribosomes
- RNA
- other Protiens
What do ribosomes do
- Site of mRNA translation
- Site of protein synthesis
What are ribosomes made up of
2 sub units
(Large and Small)
Where are ribosomes assembled
Assembled in the nucleolus of the nucleus and exported into the cytoplasm.
What do the different ribosomes make protiens for
- Ribosomes in the cytoplasm make protiens for use in the cell
- Ribosomes made in the RER make protiens for export
Where is tRNA made
In the nucleus
