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IB Bio HL > A1.2: Nucleic Acids > Flashcards

A1.2: Nucleic Acids Flashcards

1
Q

What are nucleic acids?

A

Polymers
-> monomers: nucleotides
Used for storage/transfer of information

Two main functions:
Pass info between generations through DNA replication
Code for protein production

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2
Q

What are the 2 main types of nucleic acids?

A

DNA -> deoxyribnucleic acid
-> pass info
-> code for RNA

RNA -> ribonuceleic acid
-> code for proteins
-> 3 types: mRNA, rRNA, tRNA

Both polynucleotides -> long chains of nucleotides

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3
Q

DNA/RNA as the genetic material of living organisms

A

Carries genetic code in all living organisms -> universal -> all forms of life

Mainly found in nucleus in chromosomes
-> also in chloroplasts and mitochondria

RNA -> main component = ribosomes
-> role in protein synthesis
-> little RNA in nucleus and cytoplasm

Certain virus -> RNA instead of DNA

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4
Q

Structure of a nucleotide

A

RNA and DNA -> polymers made of repeated nucleotide units

Pentose sugar
-> ribose or deoxyribose

Nitrogenous base
- Purine:
-> Adenine and guanine
- Pyrimidine:
-> Cytosine
-> Thymine (in DNA) and Uracil (in RNA)

A phosphate group
-> acidic
-> neg charge

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5
Q

What are the main functions of nucleotides?

A

Formation of DNA and RNA
Form parts of molecules needed for metabolism
-> adenine -> adenosine triphosphate (ATP)

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6
Q

What type of bonds are formed within and between nucleotides?

A

Between: covalent bond

Within:
- base and sugar join with a glycosidic bond
- phosphate and sugar join with an ester bond
-> both require a condensation reaction

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7
Q

How do nucleotides bond with each other?

A

Condensation reaction:
Phosphate group of one nucleotide + pentose sugar of the next one -> covalent bond

Forms sugar-phosphate backbone

-> repeated and forms polymer -> nucleic acids/polynucleotides -> strand

-> DNA double strand
-> RNA single strand

4 different bases that can be join in any combination/sequence

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8
Q

How do the bases bond together?

A

Purine -> double ringed structure
Pyrimidine -> single ringed structure

Complementary base pairing:
Purine + pyrimidine -> base pair

-> A to T (DNA) / A to U (RNA)
-> 2 H bonds

-> C to G
-> 3 H bonds

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9
Q

RNA characteristics

A

Nucleotides -> ribose
Bases -> Uracil (x thymine)
Single stranded

Short molecule
-> length of 100s - 1000s nucleotides

Three types:
-> rRNA -> ribosomal
-> tRNA -> transfer (translation to transport specific AA coded in mRNA to ribosome -> protein synthesis)
-> mRNA -> messenger (formed by transcription, copy of DNA, read by ribosome -> polypeptide)

Adjacent RNA nucleotides -> linked via condensation reactions -> phosphodiester bonds

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10
Q

What is the shape/structure of DNA?

A

Double helix made of two antiparallel strands of nucleotides linked by hydrogen bonding between complementary base pairs

Each DNA nucleotide -> 3’ and 5’ end
-> one strand 3-5
-> other strand 5-3

Bases towards interior
-> H bonds between bases hold together double helix

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11
Q

What are the difference between DNA and RNA?

A

DNA: thymine
RNA: uracil

DNA: deoxyribose
RNA: ribose

DNA: double strands
RNA: single stranded

DNA: long chains
RNA: short chains

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12
Q

T or F: complementary base pairing plays no role in the replication and expression of genetic information

A

False

Complementary base pairing ALLOWS DNA to be copied precisely during replication/copied accurately -> expressed accurately

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13
Q

Diversity of possible DNA base sequences

A

Despite only 4 bases -> can form large range of DNA base sequences

DNA -> limitless capacity for storing information

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14
Q

How can genetic information storage capacity be measured?

A

Number of gene contained within the DNA of an organism
Ex: humans 20,000
Dog 19,000
Rice plant 41,500

Number of base pairs contain within the genome of an organism
-> based pairs -> DNA with about 2m length -> in nucleus
-> basically DNA well packaged
-> enormous capacity for storing genetic data

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15
Q

Genetic code - forming a polypeptide

A

DNA -> carry genetic code as sequence of nitrogenous bases in nucleotides

1 strand DNA -> base sequence read by enzymes -> coding strand

Sequence of bases that form genes on coding strand -> determine order of AA in protein

Code read in triplets of bases (codons) -> 3 bases = 1 AA

Sequences of AA -> determine shape and function of protein

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16
Q

Universality of genetic code: evidence for common ancestor

A

Genetic code=universal -> almost all organisms use the same code

Same codon = same AA -> genetic code transferable between species
-> genetic engineering

Evidence for universal common ancestor
-> mutations led to changed in some of the base sueqences

Base sequences -> genome of organisms
-> split into coding sequences and non-coding sequences
-> Some of these sequences remain unchanged between all organisms -> conserved sequences

High conserved sequences -> genes that code for protein involved with transcription/translation/histone protein

TLDR:
Similarity of sequences -> living organisms shared a universal ancestor

17
Q

Explain directionality of DNA

A

Nucleotides linked together -> phosphate group form bridge carbon 5 of the original sugar and the carbon 3 of the sugar its connecting to

DNA -> antiparallel -> 3-5 and 5-3

Directionally of DNA important in:
DNA replication
Transcription
Translation

18
Q

How does the directionality of DNA play a role in transcription?

A

Genetic code on one of DNA strands -> transcribed into strand of mRNA
-> read in 3-5 direction by enzymes -> synthesize mRNA into 5-3 direction

mRNA -> cytoplasm -> ribosomes (translation) -> transcribe mRNA in 5-3

Base sequence of DNA -> determine the order of AA in the polypeptide chain

Directionality of RNA/DNA -> important to ensure genetic code is correctly copied/transcribed, translated

19
Q

How did the purine+pyrimidine bonding become discovered?

How does the purine+pyrimidine help the stability of the double helix?

A

Francis Crick + James Watson worked to establish the double helix structure of DNA in 1953

Trial and error -> build model of DNA double helix where the different base pairs fit together correctly

A-T and C-G -> same length
DNA helix -> same 3D structure regardless of base sequence

Stability of double helix -> increased by hydrogen bond between base pairs

20
Q

What is a nucleosome?

A

Only DNA -> DNA associated with histone protein to form chromatin

Strand of DNA coiled around a core of 8 histone proteins (octamer) -> bead like structure

Nucleosomes can be tagged with proteins -> promote or suppress transcription

Prophase (of mito or mei) -> condense even more -> supercoil into chromosomes -> prevent tangling/damage

DNA un-packaging -> transcription/replication require DNA to temporarily release from histone -> return to compact state

21
Q

What is the structure of nucleosomes?

A

DNA takes 2 turns around histone core
Held in place by additional histone protein -> attached to linker DNA

-> Histone -> Pos charge
-> DNA (bc of phosphate group) -> neg charge
= bind tightly via electromagnetic tension

DNA molecules repeatedly wound around -> series of nucleosome
-> nucleosomes supercoil the DNA -> compact structure
-> also protect DNA
-> facilitate movement of chromosomes during cell division

22
Q

Explain the Hershey-Chase experiment

A

DNA identified in 1869 -> but scientist still thought protein was the heritable material

1950s: Alfred Hershey and Martha Chase -> DNA (not protein) is a factor of heredity responsible for carrying genetic info from gen to gen

Used virus that infect bacteria -> used in experiment
-> used bc they were only DNA with protein coat
-> allowed bio molecule of heredity to be easily determined

23
Q

What was the procedure of the Hershey-Chase experiment?

A

They took advantage of chemical difference:
DNA -> phosphorous
Protein -> sulfur

virus -> S-35 labelled protein coat or p-32 labelled DNA interior

Unlabelled bacteria -> infected separately with either type of virus
-> bacteria expected to contain heritable material following infection (S or P)
-> virus inject its genetic material into bacteria

Blender -> used to remove attached virus from bacteria
Centrifugation -> isolate bacteria
-> virus small so remained in supernatant
-> bacteria larger -> pellet

Only bacteria infected with P-32 labelled virus -> radioactive

Suggested that: DNA was transferred to bacteria and is the hereditary genetic material

24
Q

Explains Chargaffs data

A

Erwin Chargaffanalysed theDNA composition of different organismsduring the 1930s and 1940s and made the following discoveries:

Number of purine bases = number of pyrimidine bases

Number of adenine bases = number of thymine bases
Number of guanine bases = number of cytosine bases

Meaning that:
Purine base can only pair with pyrimidine base (due to their sizes)
This forms foundation of complementary base pairing in DNA

25
Q

What is the problem of induction?

A

Inductive scientific method :
-> scientist making observation and collecting raw data
-> After data analysis
-> hypothesis formed
-> tested by suitable investigation
-> general conclusions being drawn based on observations
-> data from past used to create general predictions about the future (assume future will be the same)

Therefore:
Possible to prove a hypothesis generated by inductive reasoning as true
Cannot be sure observations made in past = observations in the future

= problem of induction
-> why scientific theories -> tentative

Even if many investigation support hypothesis -> can be proven incorrect in future

For this reason -> Karl Popper (philosopher) suggest new scientific knowledge in not gained by inductive steps but rather by the falsification of existing hypotheses

26
Q

Explain the falsification of the tetranucleotide hypothesis

A

the biochemistPhoebus Levenediscovered thepentose sugarsof DNA and RNA in the early 1900’s
-> suggested that the structure of nucleic acid was arepeating tetramer unitwhich he called a nucleotide
-> this was called thetetranucleotide hypothesis

At the time of his research -> limitations to analytic techniques available -> difficult to determine relative amount of nucleotides present

Tetra nucleotide hypothesis -> falsified by Chargaffs data (late 1940s)
Further disproven when structure of DNA determined in 1950s

IB Bio HL (9 decks)

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