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Grade 12 Biology > Unit 4: Genetics > Flashcards

Unit 4: Genetics Flashcards

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1
Q

Mendel’s contributions

A

1860s
Used pea plants to selectively breed for colour
Found alleles, and that one allele tends to be dominant

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2
Q

Griffith

A

1920s
Used bacteria (streptococcus pneumonia): S-type (smooth colonies) R-type (rough colonies –lack a capsule)
Introduced the strains to mice
Something in heat-killed S-type cells was transferred to the R-type causing them to be lethal

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3
Q

Hammerling

A

1930s
Determined feet of algae contained traits (transplanted severed heads onto feet)
Then used microscope to observe nucleus in feet
Conclusion: traits stored in nucleus

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4
Q

Avery

A

1940s
Wanted to determine which molecule contained trait information
Extracted various chemical components from bacteria (carbs, lipids, protein, DNA)
Demonstrated that transformation stopped by enzymes that digest DNA
Conclusion: DNA is the hereditary molecule in bacteria

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5
Q

Chargraff

A

1942
Studied Nitrogenous base composition of DNA
2 Conclusions
Base composition varies from species to species
The percentages of A and T are equal; as are the percentages of C and G

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6
Q

Hershey and Chase

A

1952
Used Radio-labelling
Radiolabeled phosphorus detected in bacterial cells
Viral DNA enters bacterial cells
Viral proteins do not enter bacteria cells during infection
DNA only thing that enters the cell therefore must be genetic material

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7
Q

Franklin/ Watson and Crick

A

1953
Used available data including Chargaff’s ratios and Franklin’s X-ray crystallography
Built models to work out the structure of DNA
DNA is a twisted (helical) ladder in which sugar-phosphates form the sides (backbone) and paired, hydrogen bonded nitrogenous bases make up the rungs

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8
Q

Explain the nucleotide structure.

A 
C1 links nitrogenous base to ribose
C2  differs between DNA and RNA
H vs OH
C3 inks nucleotide subunits (via phosphate)
C4 hangs out
C5 links phosphate group
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9
Q

What is the DNA backbone?

A

Sugar phosphate backbone joins carbon 3 and carbon 5 via the phosphate group

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10
Q

Anti Parallel strands:
What direction to complementary strands run?
What are the 3 and 5 ends?

A

Complementary strands run in opposite directions
Refer to the 3’ and 5’ ends of the DNA
3 = sugar (carbon 3)
5 = phosphate (C5

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11
Q

What are the number of H-Bonds in base pairs?

A

A:T
2 H-bonds
C:G
3 H-bonds

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12
Q

Meselson and Stahl

A

1958
Parent cells: DNA was most dense containing N-15
1st generation: all DNA is of ‘intermediate density’ compared to parent cells
2nd generation: two bands of DNA, half ‘intermediate’ and half ‘low density DNA’

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13
Q

When does DNA replication occur?

A

During interphase

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14
Q

What is semiconservative replication?

A

Each strand of the DNA acts as a template upon which a new DNA strand is built.

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15
Q

What is the replication fork/bubble?

A

Fork occurs for more primitive organisms (prokaryotes) with less DNA to copy
Bubbles occur in eukaryotes where multiple forks approach each other

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16
Q

How does DNA Replication work (4 steps)

A

Helicase unwinds DNA and breaks H-bonds creating a replication fork as it moves
Single Stranded binding proteins (SSB) stabilize the DNA strands while they are separated
Gyrase alleviates supercoiling stress as the DNA unwinds by temporarily nicking one strand and allowing the DNA to uncoil
RNA Primase makes RNA primers that are complementary to the exposed 3’ ends

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17
Q

What does DNA polymerase III do? What direction does it read and synthesize?

A

Binds to RNA primers and lengthens them by selecting free nucleotides that are complementary to the exposed DNA nucleotides
DNA polymerase moves (reads) in the 3’ to 5’ direction and synthesizes in the 5’ to 3’ direction

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18
Q

What does the leading strand do?

A

Forms continuously by adding nucleotides in the 5’ to 3’ direction as the replication fork proceeds

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19
Q

What does lagging strand do?

A

Forms from the inside-out in numerous sections called Okazaki fragments
Multiple RNA primers have to be laid down as the fork exposes new sections of nitrogenous bases

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20
Q

What does DNA polymerase I do?

A

Removes RNA primers from leading and lagging strands and replaces them with the appropriate complementary deoxyribonucleotides

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21
Q

What does ligase do?

A

Joins Okazaki fragments into a single strand by creating phosphodiester bonds between them

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22
Q

What is the structure of RNA?

A

Single stranded polymer of nucleotides
Contains ribose sugar (instead of deoxyribose)
Contains uracil (instead of thymine)

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23
Q

How many codons (specify amino acids) are there?

A

There are 61 codons

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24
Q

What is the start codon?

A

AUG/methionine

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25
Q

What are the three stop codons?

A

UAA, UAG, UGA

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26
Q

What is the promoter region?

A

Often called the ‘TATA box’, a string of As and Ts at the 5’ end of the coding strand of DNA upstream from a gene
The enzyme RNA polymerase recognizes and binds to this site initiating mRNA synthesis

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27
Q

What does transcription do?

A

DNA → RNA

28
Q

What are the phases of transcription?

A

Initiation: RNA polymerase binds to TATA box promoter ‘upstream’ from a gene
May require ‘transcription factors’ (helpers) to bind
Elongation: RNA polymerase opens DNA and adds nucleotides in the 5’ → 3’ direction
DNA strands re-anneal as polymerase passes ‘downstream’
Termination: RNA polymerase reaches termination sequence downstream from gene.
RNA polymerase released from DNA along with mRNA ‘transcript’ of the gene

29
Q

What are exons and introns?

A

Eukaryotic genes contain both ‘coding regions’ (exons) and ‘non-coding regions’ (introns)

30
Q

What do spliceosomes do?

A

Special particles called spliceosomes cut out the introns and join the remaining exons

31
Q

What is capping and tailing? Why does it occur?

A

RNA must be processed before leaving the nucleus to travel through cytoplasm to ribosome
It would otherwise be digested by enzymes in cytoplasm
Capping
7-methyl guanosine is added to the 5’ end of the mRNA = 5’ cap
Tailing
about 200 adenines (poly-A tail) are added to the 3’ end

32
Q

What do ribosomes do?

What is their structure?

A

Facilitate coupling of tRNA to mRNA codon

Structure
Ribosomal RNA (rRNA) and proteins (2 subunits, Large and Small)
33
Q

What is the shape of transfer/tRNA?

A

Folds onto itself into a cloverleaf structure stabilized by H-bonds between nitrogenous bases.

34
Q

How do you know which amino acid the tRNA will bind?

A

The codon on tRNA’s anticodon loop dictates which amino acid the enzyme ‘aminoacyl-tRNA synthetase’ will bind tRNA with an amino acid attached

35
Q

How does translation work? What are the 3 binding sites?

A

Ribosome subunits bind to the 5’ cap of the mRNA clamping around the strand
ribosome has 3 binding sites for tRNA
A site: aminoacyl-tRNA site
Holds tRNA carrying next amino acid for chain
P site: peptidyl –tRNA site
Holds tRNA carrying growing polypeptide chain
E site: exit site
Empty tRNA leaves

36
Q

How are polypeptides built (3 Steps)?

A

Initiation:
Brings together mRNA, ribosome subunits, initiator tRNA
Elongation:
Adding amino acids based on codon sequence as ribosome reads mRNA codons
Termination:
End codon: no corresponding amino acid

37
Q

What are polypeptides?

A

Chains of amino acids

38
Q

What is the wobble hypothesis?

A

Many codons can code for the same amino acid
These codons tend to only vary by the third nitrogenous base
There is some ‘wiggle room’ for errors

39
Q

What is a point mutation?

A

Point mutations mutations occur at a specific base pair in the genome

40
Q

What is a silent mutation?

A

A mutation that does not result in a change in the amino acid coded for and, therefore, does not cause any phenotypic change

41
Q

What is a missense mutation?

A

A mutation that results in the single substitution of one amino acid in the resulting polypeptide

42
Q

What is a nonsense mutation?

A

A mutation that converts a codon for an amino acid into a termination codon

43
Q

What is a frameshift mutation?

A

A mutation that causes the reading frame of codons to change, usually resulting in different amino acids being incorporated into the polypeptide

44
Q

What is translocation?

A

The transfer of a fragment of DNA from one site in the genome to another location

45
Q

What are transposable elements?

A

Segments of DNA that are replicated as a unit from one location to another on chromosomal DNA

46
Q

What is an inversion?

A

The reversal of a segment of DNA within a chromosome

47
Q

What are spontaneous mutations?

A

Mutations occurring without chemical change or radiation but as a result of errors made in DNA replication

48
Q

What are mutagenic agents?

A

Agents that can cause a mutation

49
Q

Describe how UV is a mutagenic agent

A

UV light possesses more energy than visible or infrared light; a high- frequency UV light contains enough energy to cause a point mutation.

50
Q

Describe how xrays are mutagenic agents

A

X rays are high-frequency, high-energy radiation and have the ability to break the backbone of a DNA molecule.

51
Q

What are oncogenes?

A

Mutant versions of genes that control cell growth and division.

52
Q

What is gene regulation?

A

The turning ‘on’ or ‘off’ of specific genes depending on the requirements of the cell

53
Q

What do prokaryotic cells use for gene regulation?

A

Operons

54
Q

What are operons?

A

A simple regulatory loop in which a cluster of genes are under the control of a promoter and an operator

55
Q

What is a promoter?

A

The binding site on DNA for RNA polymerase

56
Q

What is an operator?

A

The binding site on DNA where a repressor protein will bind

57
Q

What is a repressor protein?

A

A protein that binds to operator site on DNA and prevents transcription of operon genes

58
Q

What is an inducer?

A

A molecule that binds to repressor protein causing conformational changes that results in the protein’s removal from operator

59
Q

What is a co-repressor?

A

A molecule that binds to a repressor to activate it

60
Q

How do repressor proteins work?

A

If a repressor protein is bonded to the operator site, RNA polymerase is unable to pass and cannot transcribe the DNA
Gene expression is repressed

61
Q

What does a tryptophan operator consist of?

A

Tryptophan Operon consists of
A promoter sequence (P)
An operator (O)
Five genes that code for polypeptides that combine to form 3 enzymes required for the synthesis of tryptophan

62
Q

What happens if Tryptophan levels are high?

A

Tryptophan is plentiful and because there is so much, it acts as it’s own corepressor
It binds to the repressor protein and changes its shape so that it is able to bind to the operator site
RNA polymerase is blocked from transcribing trp operon

63
Q

What happens if Tryptophan levels are low?

A

In absence of tryptophan, there is no corepressor to bind to the trp repressor protein
Trp repressor protein cannot bind to operator site without tryptophan co-repressor
RNA polymerase is not blocked, trp operon genes are transcribed
Cell can synthesize tryptophan.

64
Q

What is the lac operon?

A

Inducible operon that’s involved in the metabolism of lactose (dissacharide) to be used as energy source if available
Enzyme β-galactosidase is involved in thehydrolysis of lactose. If lactose is not present, β-galactosidase is not necessary (nothing for it to break down)
The gene for β-galactosidase is part of the lac operon

65
Q

What are the components of a lac operon?

A

A promotor sequence
An operator sequence
A cluster of 3 genes that code for proteins involved in the metabolism of lactose
Upstream of the operon is another gene called LacI which codes for the ‘LacI protein’ or ‘lac repressor protein’

66
Q

How does lactose work?

A

Lactose acts as an ‘inducer’ by binding to the ‘repressor protein’ and changing its shape
The new ‘lactose + LacI’ complex causes it to lose its ability to bind to operator and it falls off the DNA
RNA polymerase is free to transcribe lac operon genes
Transcribed genes are translated into functional proteins, cell can metabolize lactose
Plentiful
Lactose is an allosteric regulator of LacI repressor protein
Transcription is induced

67
Q

What happens if there is an absence of lactose?

A

Since there is no lactose to change the shape of the repressor protein, it is able to bind to the operator site
RNA polymerase is blocked, and unable to transcribe the gene sequence

Grade 12 Biology (3 decks)

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