DNA, genes and protein synthesis

How is DNA packed in a cell?

DNA molecules are wound around proteins known as histones to form a DNA histone complex. They then coil further to form chromatin which helps pack the DNA into chromosomes

4 differences between how DNA is stored in prokaryotic cells and eukaryotic?

Prokaryotic cells store dna in the cytoplasm whereas eukaryotic in the nucleus. Prokaryotic contain shorter circular DNA molecules whereas eukaryotic contain long linear DNA molecules. Prokaryotic do not associate the DNA with histones whereas eukaryotic do. Prokaryotic DNA does not contain introns whereas eukaryotic DNA does.

What is a gene?

A short section of DNA that codes for a polypeptide

What are exons and introns?

Exons are sections of DNA that do code for amino acids and introns do not

What is a locus?

A specific position along a chromosome whereas eukaryotic a gene is located

What is a genome?

The complete set of genes within a cell

What is a proteome?

The full range of proteins that a cell is capable of producing

What does the feature of a genetic code universal mean?

Each DNA triplet codes for the same amino acids in all organisms

What does the feature of a genetic code non overlapping mean?

Each base in the DNA sequence is only read once

What feature of a genetic code degenerate mean?

Most amino acids are coded for by more than one triplet

What is the role of mRNA?

To carry genetic information from the DNA to the ribosomes

5 features of mRNA?

Single stranded, linear, contains a base sequence complementary to a DNA sequence, contains codons, small enough to leave the nucleus

What is the role of tRNA?

To transport amino acids to ribosomes to build up a polypeptide chain

5 features of tRNA?

Single stranded, clover leaf shaped, uses hydrogen bonds between complementary base pairs to hold its shape, contains a specific sequence of three bases at one end known as anticodon, contains an amino acid binding site at the opposite end

7 steps of transcription?

1. RNA polymerase enzyme binds to DNA and breaks the hydrogen bonds between complementary DNA bases to form two strands of DNA

2. One strand acts as the template for mRNA synthesis

3. Free RNA nucleotides bind to complementary base pairs on the template

4. In the RNA molecule uracil pairs with adenine, adenine pairs with thymine and cytosine pairs with guanine

5. RNA polymerase catalyses the formation of phosphodiester bonds between adjacent RNA nucleotides

6. A complementary mRNA strand is formed and the process ends when RNA polymerase reaches a stop codon and detaches from DNA and terminates transcription

7. mRNA is released, detaches from DNA and DNA rewinds into its double helix structure

What is the difference between transcription in prokaryotes and eukaryotes?

In prokaryotes mRNA is directly produced from transcription without any splicing whereas in eukaryotes pre mRNA is spliced after transcription to remove introns before it is transported to the cytoplasm

What is translation?

The process of decoding the information in messenger RNA to synthesise a polypeptide chain with the help of trna

7 steps of translation?

1. Ribosome attaches to the mRNA strand at a start codon

2. A tRNA molecule carrying a specific amino acid and with an anticodon that is complementary to the start codon binds to mRNA

3. A second tRNA molecules with an anticodon complementary to the next mRNA codon and also carrying a specific amino acid attaches to the mRNA

4. The amino acids carried by the first two tRNA molecules are linked together via a peptide bond using ATP

5. The first tRNA molecules detaches from mRNA and is free to collect another amino acid for future use

6. The ribosome moves along mRNA allowing another tRNA molecule which carries the next amino acid to bind to the next codon on mRNA

7. This sequence continues until the ribosome reaches a stop codon on mRNA and the completed polypeptide chain detaches from the ribosome