Topic 8: DNA, Genes, Protein Synthesis

Question 1

What is a gene

Answer 1

A gene is a base sequence of DNA that codes for:
- the amino acid sequence of a polypeptide
- a functional RNA

Question 2

What do you call the fixed position of the gene on a DNA molecule

Answer 2

Locus

Question 3

Where is DNA found

Answer 3

Mostly in nucleus
(also in mitochondria as mitochondial dna)

Question 4

What are the 4 bases of DNA

Answer 4

• Adenine
• Thymine
• Cytosine
• Guanine

Question 5

What is a codon

Answer 5

A sequence of three bases that codes for a single amino acid

Question 6

How many amino acids are coded for in protein synthesis

Answer 6

20 amino acids

(because some have multiple codes)

Question 7

What does it meanby the genetic code being degenerate

Answer 7

several code words have the same meaning (amino acid)

Question 8

What are stop codes

Answer 8

When the codon does not code for an amino acid, but for the ribosome to stop the polypepetide chain

Question 9

What is always the start codon

Answer 9

Methionine
(AUG)

Question 10

What does it mean by the code is non-overlapping

Answer 10

Each base is only read once, and the triplets are read in the same direction

Question 11

What does it mean by the code being universal

Answer 11

The genetic code is the same in almost every living being, with a few specific exceptions.

Question 12

What do you call a sequence that does not code for an amino acid

Answer 12

Introns

Question 13

What do you call a sequence that codes for an amino acid

Answer 13

Exons

Question 14

What happens to the introns

Answer 14

They are removed by splicing before the final mRNA reach the ribosomes.

Question 15

What do you call the proteins associated with DNS

Answer 15

Histones

Question 16

What forms a chromosone

Answer 16

DNA molecule and its associated proteins (histones)

Question 17

When the cell is not dividing, what are the chromosones like?

Answer 17

• not visible
• uncoiled
• loosely found throughout nucleus

Question 18

How do chromosones appear at the start of cell division

Answer 18

Two threads joined at a central point (centromere).

Question 19

What does each chromosone consist of

Answer 19

• two identical DNA molecules (chromatids)
• held together by proteins called histones.

Question 20

How are chromatids of a chromosone produced?

Answer 20

• The DNA helix is wound tightly around histones acting as packaging proteins, forming a nucleosome.
• A series of nucleososmes looks like beads on a string in an electron micrograph.
• The string of nucleosomes then loops and coils into the *30nm fibre. *
• The 30nm fibre folds up further into a 300nm wide supercoil.
• This then produce the chromatid of a chromosome.

Question 21

What is the advantage of DNA coiling?

Answer 21

A lot of DNA can be packed into the chromosome, with each chromosome consisting of a single, very long strand of DNA.

Question 22

What is a homologous pair

Answer 22

• two copies of each chromosome
• always carry same genes but may have different alleles of the genes.

Question 23

During meiosis, what happens to the number of chromosones

Answer 23

number of chromosomes is halved and this is controlled so that each daughter cell end up with one chromosome from each homologous pair.

Question 24

What is an allele

Answer 24

One of a number of different forms of the same gene.

Question 25

How do you inherit alleles (sexual organisms)

Answer 25

• One allele from mum
• One allele from dad

(Can be different or the same)

Question 26

What happens if the two inherited alleles are different

Answer 26

The result will be two different polypeptides being expressed.

Question 27

What happens to the allele if there is a mutation

Answer 27

A new allele will form, producing a different polypeptide

Question 28

What is an organisms genome

Answer 28

The complete set of genes in a cell, including those in mitochondria and chloroplasts.

Question 29

What is the proteome

Answer 29

The full range of proteins produced by the genome

Question 30

Where does the synthesis of proteins happen?

Answer 30

In the cytoplasm
(in the ribosomes)

Question 31

What is the function of mRNA

Answer 31

To transfer information from the nucleus to the ribosome

Question 32

Name four differences between RNA and DNA

Answer 32

1. RNA has the sugar ribose instead of deoxyribose
2. RNA has the base uracil instead of thymine
3. RNA is usually single stranded, but can fold into 3-dimentional structures, like proteins.
4. RNA is usually shorter than DNA

Question 33

How long is mRNA

Answer 33

One gene long

Question 34

How does the codon bind to a tRNA molecule

Answer 34

Using the anticodon of the tRNA

Question 35

What are some features of a tRNA molecule

Answer 35

• One end has the amino acid bidning site
• One end has the anticodon which is a triplet code to bind to the codon
• Clover shaped

Question 36

How are the amino acids attatched to the tRNA molecule

Answer 36

By specific **aminoacyl tRNA synthase enzymes. **

Question 37

What two things form ribosomes

Answer 37

• RNA
• other Protiens

Question 38

What do ribosomes do

Answer 38

• Site of mRNA translation
• Site of protein synthesis

Question 39

What are ribosomes made up of

Answer 39

2 sub units
(Large and Small)

Question 40

Where are ribosomes assembled

Answer 40

Assembled in the nucleolus of the nucleus and exported into the cytoplasm.

Question 41

What do the different ribosomes make protiens for

Answer 41

• Ribosomes in the cytoplasm make protiens for use in the cell
• Ribosomes made in the RER make protiens for export

Question 42

Where is tRNA made

Answer 42

In the nucleus