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8: DNA, genes and protein synthesis

Biology20 CardsCreated 3 months ago

This deck covers key concepts related to DNA, genes, and protein synthesis, including the structure and function of genetic material, the process of transcription and translation, and the genetic code.

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What is a gene?

Section of DNA on a chromosome that codes for one or more polypeptides.
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Key Terms

Term
Definition
What is a gene?
Section of DNA on a chromosome that codes for one or more polypeptides.
Why is the genetic code described as degenerate?
Most amino acids are coded for by more than one triplet.
Why is the genetic code described as non-overlapping?
Each base sequence is only read once.
Why is the genetic code described as universal?
Exists in all organisms.
What are exons?
Regions of the gene which are coding.
What are introns?
Non-coding sequences.
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8: DNA, genes and protein synthesis
TermDefinition
What is a gene?
Section of DNA on a chromosome that codes for one or more polypeptides.
Why is the genetic code described as degenerate?
Most amino acids are coded for by more than one triplet.
Why is the genetic code described as non-overlapping?
Each base sequence is only read once.
Why is the genetic code described as universal?
Exists in all organisms.
What are exons?
Regions of the gene which are coding.
What are introns?
Non-coding sequences.
Structure of chromosome?
DNA combine with histones. DNA-histone complex is coiled. Coils fold to form loops. Loops coil and pack together to form the chromosome.
What are homologous pairs of chromosomes?
A pair of chromosomes, one maternal and one paternal that have the same gene loci and therefore determine the same features.
What is an allele?
One of a number of alternative forms of a gene.
What happens to alleles when there is a mutation?
Any changes in the base sequence of a gene produces a new allele of that gene and results in a different sequence of amino acids being coded for leading to the production of a different polypeptide.
Genome?
The complete set of genes in a cell.
Proteome?
Full range of proteins produced by the genome.

Structure of RNA?

  • pentose sugar ribose

  • organic base

  • phosphate group

mRNA

single polynucleotide chain
single helix shape
molecule is smaller than DNA but larger than tRNA
pentose sugar is ribose
organic bases are adenine guanine cytosine and uracil
manufactured in the nucleus but found throughout the cell
less stable than DNA or tRNApolynucleotide chain.

tRNA

single polynucleotide chain
clover shape
smallest molecule of the three
pentose sugar is ribose
organic bases are adenine guanine cytosine and uracil
manufactured in the nucleus but found throughout the cell
more stable than mRNA but less than DNA

Transcription

Occurs in the nucleus
1. DNA helix unwinds to expose the bases to act as a template
2. only one strand of DNA acts as a template
3.unwinding is catalysed by DNA helices which breaks the hydrogen bonds between the complementary bases
4. free mRNA nucleotides in the nucleus align opposite exposed complementary DNA bases
5. RNA polymerase bonds together the nucleotides to form a new RNA chain which is pre-mRNA
6. when RNA polymerase reaches a stop triplet it detaches

Why does transcription have to occur instead of DNA leaving the nucleus?
DNA is too large to leave the nucleus through the nuclear pores. Enzymes in cytoplasm could damage DNA.
Splicing of pre-mRNA?
Introns are non-coding sections of DNA. They are spliced out by spliceosome.

Translation

  1. modified mRNA leaves the nucleus through nuclear pores and attaches to a ribosome in the cytoplasm

  2. the ribosome attaches at the start codon

  3. the tRNA molecule with the complementary anticodon to the start codon will align opposite the mRNA held in place by the ribosome

  4. the ribosome will move along the mRNA molecule to allow other complementary tRNA to attach to the next codon on the mRNA

  5. the two amino acids that have been delivered by the tRNA molecule are joined by a peptide bond. This is catalysed by an enzyme and requires ATP

  6. this continues until the ribosome meets the stop codon at the end of the mRNA molecule. The stop codon does not code for an amino acid and therefore the ribosome detaches

  7. polypeptide is now created and enters the golgi apparatus for modification and folding

What is a codon?
A sequence of 3 adjacent nucleotides in mRNA that code for an amino acid.