Biology U4 T1 - DNA, Genes, and the Continuity of Life

Question 1

Describe the structure of DNA

Answer 1

Double helix structure, bound to histones in chromosomes in nucleus, unbound in prokaryotes cytosol, in mitochondria and chloroplasts in eukaryotes, pentose sugar, phosphate group, nitrogenous bases, sugar phosphate backbone (5’ to 3’)

Question 2

DNA replication

Answer 2

Helicase breaks the hydrogen bonds between bases (unzips DNA)
Leading (5’ to 3’):
RNA primer bind to start of strand
DNA polymerase adds complementary bases
Continuous replication
Lagging (3’ to 5’):
Multiple RNA primers added
DNA polymerase adds chunks of complementary DNA (Okazaki fragments)
Discontinuous replication
Exonuclease strips primers
DNA polymerase fills in gaps in bases
DNA polymerase proofreads bases
DNA ligase seals strands
Strands twist into double helix structure

Question 3

Meiosis I and II

Answer 3

Meiosis I
Prophase I
Centrioles to opposite sides of cell
Spindle fibres appear
Nuclear membrane breaks down
Homologous proteins pair off
Crossing over occurs
Metaphase I
Homologous chromosomes align in middle next to duplicates
Spindle fibres attach
Anaphase I
Spindle fibres pull apart
Chromosomes are split
Telophase I
Cytoplasm divides
Two cells
Nuclear membrane reforms

Meiosis II
Prophase II
Centrioles to opposite sides of cell
Spindle fibres appear
Nuclear membrane breaks down
Metaphase II
Spindle fibres attach
Chromosomes to middle of cell
Anaphase II
Spindle fibres retract
Sister chromatids are split
Telophase II
Four daughter cells

Question 4

Crossing over and recombination

Answer 4

the process of chromosomes overlapping randomly and genetic material is exchanged, creating different genomes

Question 5

Spermatogenesis

Answer 5

Embryo – diploid spermatogonium form
After puberty – spermatogonium form diploid primary spermatocyte
Meiosis I – haploid secondary spermatocytes form
Meiosis II – spermatids form
Four functionally genetically unique sperm cells

Question 6

Genotype and phenotype

Answer 6

• Genotype is an organism’s genetic composition
• Phenotype is the way genes are expressed in characteristics

Question 7

Autosomal dominant inheritance

Answer 7

dictates that the genotype and phenotype will exhibit the dominant traits (capital letters)

Question 8

Independent assortment

Answer 8

the random alignment of homologous chromosomes to the other side of the cell

Question 9

Random fertilisation

Answer 9

the principle that any egg or sperm has the same chance of being fertilised

Question 10

Genome

Answer 10

the complete set of genetic information in an organism

Question 11

Gene

Answer 11

a specific region of DNA that codes to produce a functional protein

Question 12

Structure of a gene

Answer 12

Exons (coding), introns (non-coding), centromeres, telomeres, proteins

Question 13

Protein synthesis

Answer 13

Transcription converts DNA into mRNA (nucleus)
RNA polymerase unzips the DNA
RNA polymerase attaches to promoter region (identifies gene to express)
RNA polymerase creates complementary strand
Continues until STOP triplet

Translation translates mRNA into a functional protein (ribosomes)
tRNA molecule with START amino acid and anticodon attaches to mRNA
amino acids join to form a polypeptide chain
protein is released

Question 14

Gene expression

Answer 14

• Differential gene expression enables cell differentiation and directs morphological changes
• Gene regulation controls gene expression and determines what proteins are necessary to be produced

Question 15

Transcription factor genes

Answer 15

Homeobox (HOX) gene - Control correct tissue formation and development of body segments
Sex-determination range Y (SRY) gene - Chance of turning on during gestation to develop male organs and hormones

Question 16

Point/frameshift mutations

Answer 16

Point mutations - silent (harmless), missense (harmful), nonsense (stop)

Frameshift mutations - insertion, deletion

Question 17

Nondisjunction

Answer 17

occurs when the chromosomes fail to separate correctly during meiosis

Question 18

Mutagens

Answer 18

environmental factors that can induce mutations

Question 19

Aneuploidy

Answer 19

the abnormal number of chromosomes in the daughter cell which is a direct result of nondisjunction occurring

Question 20

Down, Klinefelter, Turner, Patau syndrome

Answer 20

Down syndrome – trisomy 21
Klinefelter syndrome – extra X chromosome
Turner syndrome – missing part of X chromosome
Patau syndrome – trisomy 13

Question 21

Sex-linked inheritance

Answer 21

traits that are only found on sex chromosomes (X and Y)

Question 22

Allele

Answer 22

a different version of the same gene (hair colour is a gene, brown is an allele)

Question 23

Polygenic inheritance

Answer 23

when two or more genes are responsible for a trait

Question 24

Recombinant DNA

Answer 24

• Cut target species DNA with restriction enzyme
• Insert DNA into bacterial plasmid to create a recombined plasmid factor
• Join the DNA with DNA ligase
• Amplify the bacteria

Question 25

Purpose of DNA sequencing

Answer 25

determines the order of nitrogenous bases (A, T, C, G) of a species’ genetic information
* Known and new mutations, disease detection and treatment, potential evolutionary change

Question 26

Polymerase chain reaction and gel electrophoresis

Answer 26

Polymerase chain reaction creates copies of DNA
Denaturation – heated to break hydrogen bonds
Annealing – cooled to allow primers to bind to template DNA
Elongation – reheated to allow Taq polymerase to synthesise DNA from primer

Gel electrophoresis tests unknown DNA samples against known samples to determine similarity
Uses methylene blue solution in combination with a DNA ladder

Question 27

Oogenesis

Answer 27

Embryo – diploid oogonium form
Meiosis I – diploid primary oocyte
Puberty – haploid secondary oocyte and a polar body
Meiosis II – only completed if secondary oocyte is fertilised
Only one functionally genetically unique ovum