DNA, genes, protein synthesis

Question 1

Describe the DNA in a eukaryotic cell

Answer 1

Packaged as chromosomes in the nucleus and is linear, and associated with proteins called histones, together forming chromatin.

Question 2

Describe the DNA in a prokaryotic cell

Answer 2

Short, circular, and not associated with proteins, condenses by supercoiling.

Question 3

There are 2 grooves in a double helix of DNA, what are their names?

Answer 3

Major groove
Minor groove

Question 4

What protein causes DNA to coil to form chromosomes?

Answer 4

Histone

DNA winds itself around this and it also helps to support DNA.

Question 5

How many chromosomes do we have?

Answer 5

46 individual chromosomes, (diploid number)

Question 6

What is a homologous pair?

Answer 6

A pair of matching chromosomes ( x x) .

-Have the same genes but could have different alleles.

Question 7

Define mRNA

Answer 7

Messenger ribonucleic acid, read by ribosomes in protein synthesis, single stranded.

Question 8

Define codon

Answer 8

A sequence of 3 adjacent nucleotides in mRNA that codes for one amino acid.

Question 9

What is Transcription?

Answer 9

The formation of mRNA molecules from the DNA that makes up a particular gene.

Question 10

Define genome

Answer 10

The entire set of DNA instructions found in a cell.

Question 11

Define proteome

Answer 11

The entire set of different proteins expressed in a genome, cell, tissue, or organism at a certain time.

Question 12

What is Translation?

Answer 12

The conversion of the information in mRNA to make a polypeptide.

Question 13

What is the ‘Genetic Code’?

Answer 13

The sequence of bases along its DNA, and has thousands of sections called genes, each coding for a specific polypeptide.

Question 14

The genetic code is ‘universal’, what does this mean?

Answer 14

Has the same sequence for all organisms.

Question 15

What are some differences between DNA and RNA?

Answer 15

RNA:
-Ribose
-Single stranded
-Uracil base
-Single nucleobase

DNA:
-Deoxyribose
-Double stranded
-Thymine
-Base pairs

Question 16

What is a triplet code?

Answer 16

3 bases that make an amino acid

Question 17

The triplet code is ‘degenerate’, what does this mean?

Answer 17

Each amino acid is coded for by more than one triplet.

Question 18

What does ‘non-overlapping’ mean?

Answer 18

Each base is only read once

Question 19

Briefly outline the 4 steps of protein synthesis

Answer 19

1. Transcription of the gene in the nucleus, an mRNA strand is formed.
2. Processing of the mRNA (eukaryotic)this is splicing
3. Translation of the mRNA in a ribosome, a polypeptide chain is formed.
4. Modification of the protein

Question 20

Explain the process of ‘Transcription’ in protein synthesis

Answer 20

1. Helicase breaks the hydrogen bonds in a specific region on DNA, separating the 2 strands, exposing the nucleotide bases, uncoiling.
2. One of the DNA strands is used as a template (antisense strand) to make the mRNA molecule.
3. Free nucleotides pair up with their complementary nucleotides on the strand, then RNA polymerase catalyses the formation of phosphodiester bonds.
4. As RNA polymerase is adding nucleotides, the DNA strands start to rejoin behind it, and when RNA polymerase reaches the stop triplet code called the ‘terminator region’ it detaches. (only 12 bases are exposed at one time)
5. In eukaryotic cells, the pre-mRNA is then spliced to form mRNA: the introns are removed, leaving a chain of exons. Now the mature mRNA can diffuse out of a nuclear pore and attaches to a ribosome in the cytoplasm.

Question 21

Describe the process of ‘Translation’ in protein synthesis

Answer 21

1. mRNA combines with ribosome in the cytoplasm, and tRNA attaches to amino acids within the cytoplasm.
2. Each tRNA molecule has a sequence of 3 bases called an anticodon, where they have complementary base pairs on the mRNA molecule.
3. tRNA molecules attach to the ribosome and their anticodon pairs up with the codons on the mRNA.
4. A peptide bond joins the amino acids on the tRNA, and the tRNA molecules return back to the cytoplasm.
5. The ribosome moves along there mRNA and the amino acids continues to join until a polypeptide chain is formed and it reaches a stop codon.
6. Chain disassociates from ribosome.

Question 22

What are ribosomes made from?

Answer 22

Ribosomal RNA and ribosomal protein.

Question 23

Describe the structure of tRNA

Answer 23

-Has an amino acid attachment site
-Has an anticodon
-Made from around 80 nucleotides
-Single stranded

Question 24

Define mutation

Answer 24

A change in the structure or amount of DNA.

Question 25

What is gene/point mutation?

Answer 25

Change in the base sequence of a gene which can cause a change in the polypeptide chain. It is caused by errors that occur in our DNA replication.

Question 26

What is chromosome mutation?

Answer 26

Change in the number or structure of the chromosomes. It is caused by errors that occur during cell division.

Question 27

What are the 4 types of mutations?

Answer 27

-Substitutions
-Deletions
-Insertions
-Inversions

Some can be silent, some can cause frame shift (pushes the rest along).

Question 28

Explain the ‘substitution’ mutation

Answer 28

One nucleotide in the DNA sequence is replaced by another.

It may not be harmful as the genetic code is degenerate, and the nucleotide that replaced it can still code for the same amino acid.

Question 29

Explain the ‘deletion’ mutation

Answer 29

A nucleotide in the DNA sequence is lost.

This can be harmful as it causes a ‘frame shift’ which is where the code moves along one or back, causing all of the triplets to change, and different amino acids formed (wrong ones).

Question 30

What is a frame shift?

Answer 30

When a mutation pushes the code along or back, changing the amino acids formed.

Question 31

Define the term exons and introns

Answer 31

Exons are a base sequence coding for amino acids.

Introns are non-coding base sequences, only present in eukaryotic DNA