Section 4:DNA,genes and chromosomes

Question 1

What is a gene?

Answer 1

Section of DNA, located at a certain point called the locus,on a DNA molecule

Question 2

What is the genetic code?

Answer 2

The order of bases in an organism’s DNA

Question 3

Four points

Describe properties of the genetic code

Answer 3

• Linear=read in only one way
• Degenerate=more than one triple codon that for a specific amino acid
• Non-overlapping=each triplet specifies one amino acid
• Universal code=the same base sequence always codes for the same amino acid, regardless of the species

Question 4

What is meant by punctuation codes?

Answer 4

The start and end of a sequence
The ‘start’ siginal codon AUG
The ‘stop’ siginal codon

Question 5

What are introns and extrons?

Answer 5

• Introns=non-coding sequences
• Extrons=coding sequence~needed for the protein codon

Question 6

What is DNA like in eukaryotic cells and prokaryotic cells?

Answer 6

• Prokaryotic=smaller,form circles and not associated with ribosomes
• Eukaryotic=larger,linear and associated with proteins (histones)

Question 7

How is DNA packaged in eukaryotic chromosomes?

Answer 7

• DNA combines with histone proteins
• DNA-histone complex is formed
• Coils together to form loops
• Loops coil and pack together to form the chromosome

Question 8

What are homologous pairs?

Answer 8

One maternal chromosme and one paternal chromosome, they carry the same gene but not neccesarily the same alleles of the gene

Question 9

What happens in DNA when there is a change in the base sequence?

Answer 9

• Any change in the base sequence of a gene produces a new allele=different amino acids coded for
• Leads to a different polypeptide coded for and different protein
• This different protein may not function properly or at all

Question 10

SIx points

Compare and contrast the DNA in eukaryotic cells and the DNA in prokaryotic cells

Answer 10

Comparisons:Their nucleotide structure is indentical + Nucleotides joined by phosphodiester bonds + DNA in mitochondria is structurally similar to DNA in prokayotics
Contrasts:Eukaryotic DNA is longer + Eukayotic DNA is linear/Prokayotic DNA is circular + Eukaryotic DNA contains introns but prokaryotic DNA contains no introns

Question 11

Explain how the organic bases help to stablilise the structure of DNA

Answer 11

Hydrogen bonds between the complementray base pairs hold the two strands together
Many hydrogen bonds provides collective strength

Question 12

Define genome

Answer 12

The complete set of genes in a cell, including those in the mitochondria/chloroplasts

Question 13

Define proteome

Answer 13

The full range of proteins produced by the genome

Question 14

Describe the structure of RNA

Answer 14

• Polynucleotide
• Contains the pentose sugar ribose (instead of deoxyribose-DNA)
• Contains the organic base uracil(instead of thymine-DNA)
• RNA uses information in DNA to make proteins

Question 15

Give basic function

What are the three types of RNA?

Answer 15

• mRNA~transfers genetic information from DNA to ribosomes
• rRNA~makes up ribosomes along with protein
• tRNA~involved in protein synthesis

Question 16

What is the sturcture and the role of mRNA?

Answer 16

• Structure=long strand arranged in a single helix/base sequence is determined by the base sequence of the length of DNA in transcription
• Role=mRNA leaves nucleus via nuclear pore and enters the cytoplasm where it associates with ribosomes/acts as a template for protein synthesis
• Suited for function as posses information in the form of codons

Question 17

What is the structure and role of tRNA?

Answer 17

• Structure=relatively small(80 nucleotides)/single strand folded into a clover shape held by complementary base pairing/one end of the chain extends beyond the other (where an amino acid easily attach)
• Role=each molecule has a specific anti-codon and attaches to a specific amino aicd/recognised by different enzymes

Question 18

Six points

Compare mRNA,tRNA and DNA

Answer 18

• DNA-double stranded tRNA and mRNA-single stranded
• DNA-double helix mRNA-single helix tRNA-clover shaped
• DNA-deoxyribose tRNA and mRNA-ribose
• DNA-A,T,G,C tRNA and mRNA-A,U,G,C
• DNA-mostly nucleus in eukaryotes (mitochondira/chloroplasts) mRNA-made in nucleus,found throughout cell moves into cytoplasm tRNA-made in nucleus, found throughout the cell
• DNA-chemically stable mRNA-less stable than DNA or tRNA broken down after few days to ensure protein syntheis doesn’t happen indenfinatley tRNA-more stable than mRNA less than DNA-can be reused