8.2 - DNA + Chromosomes

Question 1

What are the characteristics of DNA in prokaryotic cells?

Answer 1

• shorter
• circular
• not associated w proteins (histones)
• no introns
• contain plasmids

Question 2

What are the characteristics of DNA in eukaryotic cells?

Answer 2

• longer
• linear
• associates with proteins called histones
• has introns
• mitochondria + chloroplasts contain short, circular DNA not associated w proteins (similar to DNA in prokaryotes)

Question 3

When are chromosomes visible as distinct structures and what do they look like?

Answer 3

• when a cell is dividing
• appear as 2 threads joined at 1 point

Question 4

What protein is DNA associated with?

Answer 4

• histones

Question 5

How is a chromosome formed?

Answer 5

• double helix of DNA is wound around histones fixing it in position
• DNA-histone complex then coiled
• coil is looped + further coiled then packed into chromosome

Question 6

What is a homologous pair of chromosomes?

Answer 6

• 2 chromosomes carrying the same genes
• 1 maternal chromosome, 1 paternal chromosome

Question 7

What is the total number of chromosomes known as?

Answer 7

• diploid number

Question 8

What is the total number of chromosomes in humans?

Answer 8

• 46

Question 9

What is an allele?

Answer 9

• 1 of a number of alternative forms of a gene

Question 10

What happens when an individual inherits different alleles?

Answer 10

• each allele has a diff. base sequence
• diff. AA sequence
• diff. polypeptide produced

Question 11

What is a mutation?

Answer 11

• any change in base sequence of gene which produces a new allele of that gene

Question 12

What happens when there’s a mutation?

Answer 12

• causes diff. sequence of AA
• diff. polypeptide
• diff. protein: may not function properly/at all

Question 13

What determines the sequence of amino acids in a protein?

Answer 13

• the sequence of nucleotide bases in DNA

Question 14

Describe how a gene is a code for the production of a polypeptide.

Answer 14

• a gene is made up a sequence of bases
• that is read in triplets
• which determines the sequence of AA forming the primary structure in a polypeptide

Question 15

How is a phosphodiester bond formed between 2 nucleotides?

Answer 15

• from a condensation reaction (where 1 molecule of water is released)
• between the phosphate group + the pentose sugar (deoxyribose or ribose)
• catalysed by DNA polymerase

Question 16

How is DNA in eukaryotic cells similar to the DNA in prokaryotic cells?

Answer 16

• nucleotide structure is identical
• nucleotides joined by phosphodiester bonds
• chloroplasts + mitochondria in eukaryotic cells contain short, circular DNA not associated w proteins which is similar to DNA in prokaryotes

Question 17

Describe the structure of a DNA molecule?

Answer 17

• a double helix w 2 polynucleotide chains
• held together by hydrogen bonds
• between specific complementary base pairs

Question 18

What are ribosomes formed from?

Answer 18

• RNA
• proteins

Question 19

How are ribosomes formed?

Answer 19

• a complementary strand of mRNA is transcribed from DNA in nucleus
• mRNA travels from nucleus to the ribosomes in the cytoplasm
• ribosomes (proteins) translate mRNA into AA forming a polypeptide