protein synthesis and chromosomes

Question 1

What is a gene?

Answer 1

a base sequence (a section) of DNA, which occupies a locus (a fixed position), that codes for:

• the amino acid sequence of a polypeptide (therefore determining the proteins of an organism)
• a functional RNA (including ribosomal RNA and tRNAs )

Question 2

Which two organelles contain DNA like that of prokaryotes?

Answer 2

mitochondria and ribosomes

Question 3

What is the definition of a genome and a proteome?

Answer 3

genome - the complete set of genes in the cell

proteome= the full range of proteins that the cell is able to produce

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Question 4

Draw and label a chromosome

Answer 4

Question 5

What are homologous chromosomes?

Answer 5

carry the same genes which code for the same characteristics at the same locus, half from mum, other half from dad

can be different alleles

Question 6

What is the difference between sister chromatids and a homologous pair of chromosomes?

Answer 6

sister chromatids are identical copies of chromosomes formed during DNA replication

homologous chromosomes could be different alleles

Question 7

What is an allele?

Answer 7

an alternative form of a gene

Question 8

What is a codon?

Answer 8

three bases on mRNA that codes for a single amino acid

Question 9

What are the three types of RNA?

Answer 9

messenger RNA ,transfer RNA, ribosomal RNA

Question 10

Describe the structure of mRNA? (2)

Answer 10

• single polynucleotide strand
• the groups of three bases in mRNA is called a codon

Question 11

Describe the structure of tRNA? (4) Draw it

Answer 11

• single polynucleotide folded into a cloverleaf shape
• held by hydrogen bonds which occur between complementary base pairs within the polynucleotide
• a sequence of three bases = anticodons
• it has an amino acid binding site on the opposite end of where the anticodons are

Question 12

What is the role of mRNA?

Answer 12

carries genetic code from the DNA in the nucleus to the cytoplasm

Question 13

What is the role of tRNA?

Answer 13

carries amino acids to the ribosome during protein synthesis

Question 14

What is transcription?

Answer 14

the process of making an RNA copy of a gene sequence

Question 15

Describe the process of transcription? (exam-based)

Answer 15

occurs in the nucleolus of the nucleus

hydrogen bonds between complementry base pairs break and the DNA helix unwinds to expose the bases to act as a template

only one chain of the DNA acts as a template

free RNA nucleotides align by complementary base pairing

in RNA uracil base pairs with adenine

RNA polymerase joins adjacent nucleotide by phosphodiester bonds between adjacent nucleotides

RNA polymerase reaches a stop codon and then detaches, resulting in the formation of pre-MRNA. pre-mRNA is spliced to form mRNA

mRNA then leaves the nucleus through the nuclear envelope pores

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Question 16

What happens during the splicing of pre-mRNA? What type of cells does this only occur in?

Answer 16

ONLY HAPPENS IN EUKARYOTES

In the nucleus:

introns are removed from the pre-mRNA and exons are joined together through splicesome.

Question 17

What is translation?

Answer 17

the process in which the mRNA is ‘read’ and translated into a protein.

Question 18

Describe the process of translation?

Answer 18

A molecule of mRNA leaves the nucleus via a nuclear pore

mRNA is attached to a ribosome in the cytoplasm

the ribosome attaches at the start codon

the tRNA molecule brings a specific amino acid and then the complementary anti codon binds to complementary mRNA codons

the ribosome will move along the mRNA molecule to enable another complementary tRNA to attach to the next codon on the mRNA

the two amino acids that have been delivered by the tRNA molecules are joined by a peptide bond. this is catalyzed by an enzyme and requires ATP

trna is released after amino acid joined to polypeptide

the ribosome moves along the mRNA to form polypeptide until it reaches a stop codon

the polypeptide chain is now created and will enter the Golgi body for folding and modification

Question 19

define degenerate code and state its advantage

Answer 19

each amino acid has more than one triplet code

if a point of mutation occurs, even though the triplet bases will be different, it may still code for the same amino acid and therefore have no effect

Question 20

define non-overlapping code and state its advantages

Answer 20

each base is part of only one triplet code

if a point of mutation occurs, it will only affect one codon and therefore one amino acid

Question 21

define universal code

Answer 21

each triplet codes for the same amino acid in all organisms (indirect evidence for evolution)

his is an advantage as it means genetic engineering is possible