DNA,RNA AND protein Synethesis

Question 1

What is eukaryotic DNA like

Answer 1

Contain linear DNA molecules that exist as chromosomes-thread like structures, each made up of one long molecule of DNA and its associated proteins. Chromosomes are found in the nucleus.

The DNA molecule is really long, so it has to be wound up so it can fit into the nucleus. It’s wound around proteins called histones. His tone proteins also help support DNA. The DNA and protein is then coiled up very tightly to make a compact chromosome.

The mitochondria and chloroplasts in these cells have their own DNA. This is similar to prokaryotic DNA because it’s circular and shorter than DNA molecules in the nucleus.

Question 2

What is prokaryotic DNA like

Answer 2

Also carry DNA as chromosomes but the DNA molecules are shorter and circular. The DNA isn’t wound around histones it condenses to fit Into the cell by supercoiling.

It has no introns.

Question 3

What is a gene

Answer 3

DNA contains genes. A gene is a sequence of DNA bases / nucleotides that codes for either a polypeptide or functional RNA . The sequence of amino acids in polypeptide forms the primary structure of a protein.

Different polypeptides have a different number and order of amino acids. It’s the order of bases in a gene that determines the order of amino acids in a particular polypeptide. Each amino acid is coded for by a sequence of three bases in a gene called a triplet or codon, sequence of triplets/ bases code for protein. Non overlapping where each base is part of one codon. Degenerate code, where most amino acids have more than one codon. Of the 64 codons 1 is a start (methionine which is often removed) and three are stop codes. Often the third base is different e.g ATC and ATG might code for the same amino acid.

To make a polypeptide, DNA is first copied into messenger RNA (mRNA). This is the first stage of protein synthesis.

Genes that don’t code for a polypeptide code for functional RNA instead.

Question 4

What is functional RNA

Answer 4

RNA molecules other than mRNA which perform special tasks during protein synthesis e.g tRNA and ribosomal RNA (rRNA) which forms part of ribosomes.

Question 5

What is the genome

Answer 5

Complete set of genes

Question 6

What is a proteome

Answer 6

Full range of proteins that the cell is able to produce

Question 7

Non coding dna

Answer 7

In eukaryotes a lot of the nuclear dna doesn’t code for polypeptides. Some genes don’t code for polypeptides at all they code for functional RNA.

Question 8

What are introns

Answer 8

Genes that do code for polypeptides contain sections that don’t code for amino acids. These sections of DNA are called introns. There can be several introns within a gene and their purpose isn’t known for sure. Introns in eukaryotes are removed during protein synthesis so they don’t affect the amino acid order. Prokaryotic DNA doesn’t have introns.

Question 9

What are all the bits of gene that code for amino acids

Answer 9

Exons

Question 10

Non coding multiple repeats

Answer 10

Eukaryotic DNA also contains regions of multiple repeats outside of genes. These are DNA sequences this repeat over and over. E.g CCTTCCTTCCT.

Question 11

What other forms can a gene exist in

Give an example of an allele

Answer 11

Called alleles. The order of bases in each allele is slightly different so they code for slightly different versions of the same polypeptide.

E.g gene that codes for blood type exists as one of three alleles once codes for type O, another for type A and the other for type B

Question 12

What are homologous pairs

Answer 12

In a eukaryotic cell nucleus DNA is stored as chromosomes. Humans have 23 pairs of chromosomes , 46 in total- two number 1s, two number 2s, two number 3s etc. Pairs of matching chromosomes (e.g the 1s) are called homologous pairs.

Question 13

What is the same in a homologous pair and what’s different

Answer 13

In a homologous pair both chromosomes are the same size and have the same genes, although they could have different alleles. Alleles coding for the same characteristic will be found at the same fixed position (locus) on each chromosome in a homologous pair.

Question 14

What is protein synthesis

Answer 14

Is the production of proteins (polypeptides) from the information contained within a cell’s DNA.Its also known as polypeptide synthesis. It involves two main stages

Transcription - where the DNA code is copied into a molecule called mRNA
Translation - where the mRNA joins with an organelle called a ribosome and the code it carries is used to synthesise a protein.

Question 15

Features of RNA

Answer 15

Has a sugar ribose instead of deoxyribose
Has the base uracil instead of thymine
Usually single stranded but can fold into 3 dimensional structures like proteins
Usually shorter than DNA.

Question 16

mRNA

Answer 16

Is made during transcription. It carries the genetic code from the DNA to the ribosomes in the cytoplasm where it’s used to make a protein during translation, where proteins are synthesised.

Is a single polynucleotide strand. In mRNA groups of three adjacent bases are usually called codons.

Contain one gene only and has a short lifetime.

Degraded soon after it is used the amount of it reflects how much protein the cell is making

Question 17

Transfer RNA

Answer 17

is involved in translation
It carries the amino acids that are used to make proteins to the ribosomes.

tRNA is a single polynucleotide strand that’s folded into a clover shape.

Hydrogen bonds between specific base pairs hold the molecule in this shape.

Every tRNA molecule has a specific sequence of three bases at one end called an anticodon.

It also has an amino acid binding site at the other end.

Is an adapter that matches amino acids to their codon. tRNA is only about 80 nucleotides long and it folds up by complementary base pairing to form a looped clover shape structure. At one end of the molecule there is always the base sequence ACC where the amino acid binds. On the middle loop there is a trip,eg nucleotide sequence called the anticodon. There are 64 different tRNA molecules, each with a different anticodon sequence complementary to the 64 different codons. The amino acids are attached to their tRNA molecule by specific aminoacyl tRNA synthase enzymes. These are highly specific, so that each amino acid is attached to a tRNA adapter with the appropriate anticodon.