Genetic information, variation and relationships between organisms

Question 1

what is DNA?

Answer 1

deoxyribose nucleic acid

Question 2

what bonds hold together nitrogenous bases?

Answer 2

hydrogen bonds

Question 3

what bonds hold together the nucleotides?

Answer 3

phosphodiester bonds

Question 4

Eukaryotic DNA vs Prokaryotic DNA

Answer 4

Eukaryotic
larger/longer
associated with proteins (histomes)
found in linear chromosomes
contained within the nucleus

Prokaryotic
shorter
no protein
not in chromosomes
not in a nucleus

Question 5

what are chromosomes

Answer 5

23 pairs
maternal and paternal chromosomes
diploid if 23 pairs except gametes (sex cells as 23 in each)

Question 6

what are homologous chromosomes

Answer 6

two chromosomes that are the same by structure but they are not genetically identical

Question 7

what is a gene

Answer 7

a section of DNA that codes for a polypeptide or functional RNA

Question 8

what is an allele

Answer 8

a version of a gene

Question 9

what is the locus

Answer 9

position of an allele, same on maternal and paternal gene

Question 10

what does homologous mean

Answer 10

the same structure but not genetically identical

Question 11

MRNA vs DNA

Answer 11

MRNA 
single strand of DNA
AUCG bases
polymer
ribose sugar
short molecule

DNA
double helix structure
ATCG bases
polymer
deoxyribose sugar
long molecule

Question 12

what is transcription

Answer 12

the formation of MRNA in the nucleus

Question 13

what is translation

Answer 13

the formation of a polypeptide chain (a protein)

Question 14

how does DNA replicate

Answer 14

hydrogen bonds break by DNA helicase enzyme
free nucleotides complementary base pair with the template strand
RNA/DNA polymerase re-synthesizes the sugar phosphate back bone and forms phosphodiester bonds

Question 15

what does DNA helicase do

Answer 15

breaks hydrogen bonds and unzips double helix structure into a single strand

Question 16

what does RNA/DNA polymerase do

Answer 16

re-synthesizes the phosphate back bone and forms phosphodiester bonds

Question 17

what is a template strand

Answer 17

the strand which is being read

Question 18

what happens in transcription

Answer 18

1. DNA helicase breaks the hydrogen bonds into single strands and forms pre MRNA
2. RNA nucleotides complementary base pair
3. RNA polymerase re-synthesizes the suger phosphate backbone forming phosphodiester bonds
4. Non-coding DNA is removed (exons removed)(splicing)
5. MRNA then goes to the ribosomes

Question 19

what does MRNA and pre MRNA contain

Answer 19

MRNA - coding DNA (introns)

pre MRNA - non coding and coding DNA (introns and exons)

Question 20

what does universal mean

Answer 20

all triplet codes can code for the same amino acid

Question 21

what does degenerate mean

Answer 21

triplet codes can code for more than one amino acid

Question 22

what happens in translation

Answer 22

• MRNA attaches to ribosome
• ribosomes move to start codon
• TRNA brings specific amino acid
• anti-codon on TRNA is complementary to codon on MRNA
• ribosome moves along to the next codon
• ribosome fits around two codons
• condensation reaction occurs
• process repeated and amino acids joined by peptide bonds

Question 23

how is TRNA adapted to suit its role

Answer 23

• transports specific amino acids
• 20 different TRNA’s (degenerate)
• all share the same structure

Question 24

three types of mutation

Answer 24

• insertion
• deletion
• substitution

Question 25

what is a mutation

Answer 25

a change in one or more nucleotide base or a change in the sequence of the bases in DNA

Question 26

what is a mutagen

Answer 26

a physical or chemical agent that changes the genetic material of an organism

Question 27

factors that act as mutagenic agents

Answer 27

UV radiation
X-rays
caffeine
mustard gas

Question 28

what is a chromosomal mutation

Answer 28

changes in the number or structure of whole chromosomes

Question 29

two main types of chromosomal mutation

Answer 29

polyploidy

non-disjunction

Question 30

what happens in polyploidy

Answer 30

many copies
changes in whole sets of chromosomes
cells have multiple sets of chromosomes
3n triploid which is common in plants

Question 31

what happens in non-disjunction

Answer 31

not seperated equally
homologous pairs fail to separate
chromosome in 21, 3 in one side 1 in the other and this 1 is then destroyed
e.g downs syndrome

Question 32

meiosis vs mitosis

Answer 32

mitosis
growth and repair
1 division
2 daughter cells
46 chromosomes, 23 pairs
same genes (identical)

meiosis
a diploid nucleus divides to produce 4 haploid daughter cells
2 divisions
4 daughter cells
23 chromosomes in each
similar to parental cells but not identical

Question 33

2 main forms of genetic variation

Answer 33

crossing over

independent segregation

Question 34

what happens during crossing over

Answer 34

parts of chromosomes swap round

exchange of the alleles

Question 35

what happens during independent segregation

Answer 35

random arrangement of the chromosomes

Question 36

what is a genotype

Answer 36

the genetic makeup of an organism and the genes and alleles that they have

Question 37

what is a phenotype

Answer 37

observable characteristics - genotype + environment = phenotype

Question 38

causes of genetic variation

Answer 38

mutations
sexual reproduction
meiosis ( crossing over and independent segregation )