Genetic Information, Variation And Relationships Between Organisms

Question 1

What is a gene?

Answer 1

a section of DNA that codes for polypeptides or RNA molecules

Question 2

What do genes code for?

Answer 2

polypeptides
functional RNA, rRNA, tRNA

Question 3

What is degenerate code?

Answer 3

-multiple triplets code for the same amino acid

Question 4

What is a start code?

Answer 4

the amino acid that signifies the beginning of the polypeptide

Question 5

What is a stop code?

Answer 5

does not code for amino acids and ends the polymer
tells ribosomes the amino acid chain is done

Question 6

What is non- overlapping code?

Answer 6

each base is only read once

Question 7

What is universal code?

Answer 7

almost all triplets code for the same amino acids across living organisms

Question 8

What are exons and introns?

Answer 8

Exons are called coding sequences of DNA that are used to form polypeptides
Introns allow for a single gene to encode many transcriptions
Exons are separated by introns- non-coding sequences of bases that are removed when making mRNA

Question 9

What are chromosomes?

Answer 9

-often not individually visible
-observed in cell division
-two chromatids
-joined in the middle at the centromere

Question 10

What are homologous chromosomes?

Answer 10

-46 individuals arranged in 23 pairs
-each pair contains one chromosome from mother and one from father= homologous pairs
-homologous chromosomes contain genes at the same loci, in each pair you have 2 alleles

Question 11

What is a proteome?

Answer 11

sometimes used to refer to the proteins made by a cell in specific conditions

Question 12

What is a complete proteome?

Answer 12

the full range of proteins coded for in the genome and made by a cell.

Question 13

Properties of RNA.

Answer 13

-made up 60% of ribosomes
-made in nucleus, extra nuclear pores
-function= protein synthesis
-catalyses peptide bonds

Question 14

Properties of mRNA

Answer 14

-single stranded helix
-1000s of nucelotides
-CG,AU
-made in nucleus, DNA as template

Question 15

Structure of tRNA

Answer 15

acceptor stem
= where amino acid attaches
hydrogen bonds
= between base pairs
variable arm
=unique to each tRNA
=used for recognition
unpaired bases
=not paired to complementary base pairs
anticodon
=corresponds to the codon of mRNA
=matches up to form complementary pairs
=ensure correct amino acid is brought to the polypeptide in the correct order

Question 16

what is the function of mRNA

Answer 16

-made un the nucleus via transcription of DNA
-exists via a nuclear pore to enter the cytoplasm
-used by ribosomes as template for protein synthesis
-sequence of codons determines sequence of amino acids in primary structure of polypeptide

Question 17

what is the function of tRNA

Answer 17

=anticodon complementary to mRNA codon
=brings the correct amino acid for that codon
=facilitates the peptide bond to join the amino acids into a polypeptide

Question 18

what happens during transcription

Answer 18

-DNA helicase breaks H bonds to expose nucleotides
-free nucleotide pair up with the complementary bases on template strand
-RNA polymerase moves along one strand (template strand) to join the nucleotides
-forms pre-mRNA
-DNA polymerase rejoins hydrogen bonds after RNA polymerase passes by
-only 12 of DNA base pair are exposed at any one time
-terminator sequence detaches RNA polymerase

Question 19

what happens during translation

Answer 19

-mRNA is attracted to the ribosome
-attaches at the start codon
-moves along ‘reading’ codons
-tRNA attached to amino acid matches to complementary base strand
-temporarily bonds to mRNA , 2 bond at any one time
-peptide bond forms between 2 amino acids
-bond between tRNA and amino acid breaks and tRNA leaves empty
-ATP needed for peptide bonds to form between amino acids
-ATP needed to form bonds between tRNA and amino acid
-ribosome moves along moleculeof mRNA until it reaches a stop codon
-detaches then repeates process if necessary
-can be more than one ribosome
-each ribosome creates separate polypeptide chains
-created primary structure

Question 20

what are the two causes of genetic mutation?

Answer 20

spontaneous
-1 or 2 per 100,000 genes per generation
-varies between species
-no outside influence

mutagenic agent
(outside factors that can increase the basic mutation rate**
-high energy ionisation radiation, disrupts DNA structure
-chemicals, niitrogen diocide interferes with transcription, benzopyrene, inactivates a tumour-suppressor gene and increases likelihood of cancer

Question 21

what are the different types of genetic mutation

Answer 21

substitution
deletion
addition
duplication
inversion
translocation

Question 21

what is substitution and its after effects?

Answer 21

where one base is substituted and swapped for another base

effects:
-codes for same amino acid= no effect (degenerate code)
-codes for different amino acid that has no structural role= not much problem
-codes for different amino acid that has a structural role= could affect tertiary structure
-create stop codon= large difference in polypeptide

Question 22

what is deletion and its after effects?

Answer 22

a base on DNA that has been removed causes the rest to move along and join up leaving no gap (frame shift)

effets:
-frame shift= codons after mutation shifted and could code for all different amino acids
-could form non-functional protein which may affect phenotype
-deletion at start= every codon altered along gene= significant impact
-deletion at end= some codons altered, protein may shift

Question 22

what is addition and its after effects?

Answer 22

another base will be added to pairing strand= frame shift

effects:
-single/double additon= frame shift
-no frame shift= different polypeptide formed but may still function depending on how much/where it was added

Question 23

what is duplication and its after effects?

Answer 23

part of DNA molecule has been copied/ duplicated

effects:
-any number of bases can be duplicated so if not a multiple of 3 then frame shift occurs
-if 1 amino acid gets repeated in primary structure of polypeptide it is likely to still function
-more duplication= greater impact

Question 24

what is inversion and its after effects?

Answer 24

part of DNA structure has flipped around and re-attached itself

effects:
-may have no effect (degenerate code)
-may only affect one or two amino acids
-may from stop codon-high impact

Question 25

what is translocation and its after effects?

Answer 25

part of 1 gene is removed and stuck into another gene, happens between non-homologous chromosomes (dont have same pair or same gene)

effect:
-significant effects on gene expression
-cancers more likely
-reduced fertility

Question 26

what is polyploidy and non-disjunction and their effects?

Answer 26

polyploidy=
organisms that have an ectra set of chromosomes, mostly in plants
non-disjunction=
pairs fail to separate in meiosis giving the gamete one too many or one too little, if this gamete takes part in fertilisation a child may be born with turner’s syndrome or down syndrome

effects:
-genetic diversity for natural selection and speciation
-less well suited to environment
-cancer