DNA, genes and protein synthesis
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gene
Section of DNA that codes for making polypeptides and functional RNA -Polypeptides make proteins and so genes determine the proteins of an organisms
Homologous chromosomes
a pair of chromosomes which contains genes which code for the same characteristics -different alleles
Degenerate code
Each amino acid is coded for by more that one triplet of bases
how genes code for polypeptides
The bases in the gene provide a triplet code for amino acids. Three bases is a triplet which provides a code from one amino acid. Most amino acids are coded for by more than one triplet. The code is non-overlapping, meaning each base is read once only in a sequence.
DNA replicates by semi-conservative replication- explain what this means
DNA replication is semi conservative because each of the new strands contains one of the original strands
allele
Different forms of the same gene, which code for different polypeptides.
Where is a gene located
Locus
How is DNA stored in prokaryotic cells
In prokaryotic cells DNA is shorter and forms a circle. It is not associated with proteins, so no chromosomes are present.
Describe the structure of a chromosome
The DNA double helix is wound around histones forming a DNA histone complex. This is coiled, and folds to form loops. The loops then coil and pack together to form chromosomes. DNA is condensed into a single chromosome containing a single molecule of DNA
Explain how genes are arranged in a DNA molecule
Each DNA molecule has many genes along its length, and each gene occupies a specific position (the locus) on the DNA molecule.
How is DNA stored in Eukaryotic cells
In eukaryotic cells DNA is longer, linear and associated with proteins called histones which enable formation of chromosomes.
How is the DNA of mitochondria and chloroplasts similar to DNA of prokaryotic cells
It’s short, circular and not associated with proteins.
What are the three features of the genetic code
Universal, degenerate, non-overlapping
Genetic code
There must be a minimum of three bases that code for each amino acid
Why is it an advantage that the genetic code is degenerate
If a mutation occurs even though the triplet of bases will be different it may still code for the same amino acid and therefore have no effect
Universal
The same triplet of bases codes for the same amino acids in all organisms
Why is it an advantage that the genetic code is universal
Genetic engineering is possible
What are the four bases
Adenine, Guanine, Cytosine and Thymine
Non-overlappng
each base in a gene is only part of one triplet of bases that codes for one amino acid
What is the advantage of the genetic code being non-overlapping
If a point of mutation occurs, it will only affect one codon and therefore one amino acid.
Introns
DNA that do not code for amino acids and therefore polypeptide chains. -They get removed, spliced, out of mRNA molecules
exons
Sections of DNA that do code for amino acids
Describe how a gene is a code for the production of a polypeptide. Do not include information about transcription or translation in your answer.
• (Because) base/nucleotide sequence; • (In) triplet(s); • (Determines) order/sequence of amino acid sequence/primary structure (in polypeptide);
Not all mutations in the nucleotide sequence of a gene cause a change in the structure of a polypeptide. Give two reasons why
1.Triplets code for same amino acid/DNA/code/triplets are degenerate 2. Occurs in introns /non-coding sequence;