Unit 4, Topic 1: DNA, genes and the continuity of life

Question 1

what is the overall structure of deoxyribonucleic acid (DNA)?

Answer 1

Double-stranded helix

Question 2

What protein does DNA bind to in chromosomes in the nucleus?

Answer 2

Histones

Question 3

Where can DNA be found in eukaryotic cells?

Answer 3

nucleus, mitochondria, chloroplast

Question 4

Where can the single, circular, double-stranded DNA be found in prokaryotes?

Answer 4

In the nucleoid located in the cytoplasm.

Question 5

What is the structure of a nucleotide?

Answer 5

Phosphate, sugar, base

Question 6

What are the complementary base pairings?

Answer 6

adenine (A) and thymine (T). cytosine (C) and guanine (G)

Question 7

What is the type of bond between DNA strands?

Answer 7

Hydrogen bonds

Question 8

Explain the role of helicase and DNA polymerase in the process of DNA replication. (reference should be to the direction of replication)

Answer 8

Helicase unwinds the double helix, breaks H bonds and separates the strands. DNA polymerase pairs complementary nucleotide bases, replicates in the 5’ to 3’ direction and proofreads strand.

Question 9

What is the role of homologous chromosomes in meiosis 1 and 2?

Answer 9

They allow for the recombination and random segregation of genetic material from the mother and father into new cells which creates greater genetic diversity in the offspring.

Question 10

Describe the processes of crossing over and recombination and demonstrate how they contribute to genetic variation in meiosis 1 and 2.

Answer 10

• crossing over occurs in prophase, genetic material is exchanged between the homologous chromosomes allowing DNA from the maternal and paternal chromosomes to mix and the genes to be recombined. this allows for greater genetic variation as the chromatids in the gametes do not just have DNA from one parent.

Question 11

demonstrate how the process of independent assortment and random fertilisation alter the variations in the genotype of offspring.

Answer 11

• independent assortment occurs in metaphase and anaphase where the maternal and paternal chromosomes of each homologous pair line up and separate independently of one another. this results in the haploid gametes containing a mixture of genes from the mother and father.
• random fertilisation also increases the possible allele combinations of offspring as any egg, which contains one of the many combinations of chromosome combinations can be fertilised by any sperm cell which also contains one of the many allele combos

Question 12

are exons ‘coding’ or ‘non-coding’ DNA?

Answer 12

coding

Question 13

Define the term genome

Answer 13

all the genetic material in the chromosomes of an organism including its genes and DNA sequences.

Question 14

define the term gene

Answer 14

regions of DNA that are made up of nucleotides; the molecular unit of hereditary.

Question 15

are exons in mRNA ‘coding’ or ‘non-coding’ DNA?

Answer 15

coding

Question 16

What are the factors that regulate the phenotypic expression of genes during transcription and translation

Answer 16

Proteins that bind to specific DNA sequences to repress or activate

Question 17

Explain the process of protein synthesis in terms of transcription of a gene into messenger RNA in the nucleus.

Answer 17

DNA is unwrapped by helicase which breaks the H bonds. Transcription is the first of several steps of DNA based gene expression in which a particular segment of DNA is copied into RNA by the enzyme RNA polymerase. RNA polymerase pairs complementary nucleotide bases where uracil replaces thymine, and then it proof reads the strand. Once this is complete the mRNA (newly made strand) is ready to leave the nucleus.

Question 18

Explain the process of protein synthesis in terms of translation of mRNA into an amino acid sequence at the ribosome (refer to tRNA, codons(mRNA) and anticodons(tRNA))

Answer 18

Translation occurs in the cytoplasm at the ribosomal RNA. tRNA picks up a particular amino acid from the cytoplasm based on which anticodon is present in the tRNA. the anticodon then binds to its complementary mRNA codon. the tRNA eventually leaves and goes back to the cytoplasm and leaves behind their amino acid, resulting in an amino acid sequence, or protein, at the ribosome.

Question 19

What factors regulate phenotypic expression of genes during transcription? (2 main, activate / repress)

Answer 19

1. modification of chromatin (methylation coils = gene off)
   (acetylation unwinds = gene on)
2. products of other genes - regulatory proteins (activate by binding to DNA and enable unwinding) (repress when protein binds to region of DNA and blocks RNA polymerase from transcribing)

Question 20

Whate factor regulates phenotypic expression of genes during translation?

Answer 20

mircoRNA can bind to mRNA codons which prevents tRNA anticodons from being able to bind and create a polypeptide chain.

Question 21

What are some environmental factors that regulate phenotypic expression of genes in humans?

Answer 21

Diet, stress, pollutants

Question 22

Differential gene expression, controlled by transcription factors, regulates cell differentiation for… (2 things)

Answer 22

tissue formation and morphology

Question 23

What are some environmental factors that regulate phenotypic expression of genes in humans (affect DNA)?

Answer 23

Diet, stress, pollutants

Question 24

identify how mutations in genes and chromosomes can result from errors in DNA replication (point and frameshift)

Answer 24

Point mutation: substiution of a nucleotide base with an incorrect complementary base during replication. Does not affect rest of strand.

Frameshift mutation: the ommition or addition of one or more nucleotide bases during DNA replication. Can shift a significant portion of strand

Question 25

Identify how mutations in genes and chromosomes can result from errors in cell division (non disjunction)

Answer 25

When chromosomes do not separate appropriately in cell division. This results in one less or one more chromosome in the resultant cells, a condition called aneuploidy. This is a great change that can have a significant impact on numerous processes.

Question 26

Identify how mutations in genes and chromosomes can result from damage by PHYSICAL mutagens

Answer 26

Physical mutagens can change the DNA structure through bending it, causing the DNA to be read incorrectly during mRNA transcription and DNA replication affecting many cellular processes and leading to mutations.

Question 27

Identify how mutations in genes and chromosomes can result from damage by CHEMICAL mutagens

Answer 27

Chemical mutagens affect the nucleotide bases in the DNA strand. This affects the mRNA transcription and DNA replication as a different sequence of nucleotide bases are being used as a template than what it should be.

Question 28

Explain how non-disjunction leads to aneuploidy.

Answer 28

Non-disjunction occurs in anaphase in cell division. It results in one more or one more chromosomes being present in the resultant cells. This is a condition called aneuploidy.

Question 29

Describe how inherited mutations can alter the variations in genotype of offspring. (3)

Answer 29

Inherited mutations are permenant in the offspring. They can have no impact, small or large impact on the organism. Lastly, inherited mutations affect the control genes - homeobox genes which control embryonic development and morphology & the SRY gene on the Y chromosome that is sex-determining.

Question 30

What is autosomal dominant? (Patterns of inheritance)

Answer 30

gene is located on non-sex chromosome (numbered). If an individual inherist one of this allele from the parent, the phenotype will be expressed in the offspring

Question 31

What is sex-linked inheritance? (Patterns of inheritance)

Answer 31

The gene is located on the sex chromosomes (X and X or X and Y)

Question 32

Define polygenic inheritance.

Answer 32

When one characterisitc is controlled by two or more genes

Question 33

Describe the process of making recombinant DNA (four steps)

Answer 33

1. the plasmid DNA and DNA of the gene to be inserted is isolated and cut using restriction enzymes which result in them having complementary sticky ends.
2. insertion of DNA fragment into plasmid vector. the sticky ends pair
3. Joining of DNA gene to plasmid (DNA ligase) forming recombinant plasmids
4. Amplification of recombinant DNA when the plasmids are added to a bacteria culture and incorporated into the genome. When the bacteria reproduce by making exact copies of itself, numerous copies of the recombinant DNA is also copied.

Question 34

DNA squencing does what?

Answer 34

Maps species’ genomes

Question 35

DNA profiling does what?

Answer 35

identifies unique genetic information

Question 36

explain the process of PCR and gel electrophoresis. (three steps)

Answer 36

1. denaturation: DNA is heated to 95 degrees, breaking the H bonds between the strand’s bases and causing the strands to separate
2. Annealing: The temperature is reduced to app. 55 degrees (allows formation of H bonds), allowing primers to join to complementary sequences on opposite ends of the each strands.
3. Extention: heated to 72 degrees, optimal for DNA polymerase. Starting from the primers, new DNA stands are synthesised using DNA polymerase and available nucleotides => 2 copies of double-stranded DNA.