1.5 Nucleic acids

What is each nucleotide made of

A pentose sugar, a phosphate group and an organic nitrogenous base

what bond is formed between nuclotides

phosphodiester bonds

draw and label a typical nucleotide

what are the two main categories of nirtogenous base in nucleic acids and give examples of both and defintion

purines: guanine and adenine, they have a double ring in their structure

pyrimidines: thymine, cystosine and uracil, they have a single ring

how many bonds between adenine and thymine, and also cystosine and guanine

A-T two hydrogen bonds

C-G three hydrogen bonds

what is ATP made of and draw a pic

adenosine triphosphate

-adenine (base), ribose (pentose sugar) and three phosphate groups

what happens when ATP is broken down

broken down using hydrolysis

-third phosphate is released, forming ADP (adenosine diphosphate) and inorganic phosphate (Pi)

-releases 30.6 kj mole^-1 of energy

draw the reversible reaction of ATP being broken down and reformed

why is ATP called the universal energy currency

used by all living organisms, from bacteria to humans

why is only a small amount of energy released from ATP

-less wasteful of energy

(if it was large amounts and small amounts were needed then a lot would be wasted)

give features of DNA and what it stands for

deoxyribonucleic acid

-double helix

-two long polynucleotide strands that run in opposite direction (antiparallel)

→one strand runs from 5’ to 3’ and the other runs 3’ to 5’

-sugar is called deoxyribose meaning there is less oxygen on the ribose on carbon two

-hydrogen bonds between bases

give features of RNA and what it stands for

ribonucleic acid

-pentose sugar is ribose →one more oxygen

-uracil instead of thymine

-shorter than DNA

-single-stranded polynucleotide

what are the three types of RNA

-ribosomal RNA (rRNA)

-messenger RNA (mRNA)

-transfer RNA (tRNA)

what is rRNA function

ribosomal RNA

-forms ribosomes with the addition of protein

-made in thhe nucleolus

-highly folded to make a globular structure

what is mRNA and its function

messenger RNA

-single stranded and made in nucleus

-mRNA carries the code from DNA in the nucleus out of the nuclear into the cytoplasm and then attaches to the ribosome

what is tRNA and function

transfer RNA

-single stranded polynucleotide twisted into clover-leaf shape

-transfers correct amino acid to the growing polypeptide during translation in ribosome

-has an anticodon on one end and an amino acid on the other

what do every three bases code for and whats it called

codon

-codes for amino acid

what are the similarities between ATP and DNA+RNA

-both have adenine

-both have pentose sugar

-both have phosphate

-protein synthesis

what are the differences between ATP and DNA+RNA

-different structures

-DNA and RNA have more phosphates 

what is a gene

stretches of DNA that code for polypeptides or functional RNA

what is an exon and intron

exon: coding sequences

intron: non-coding sequences

in eukaryotes and prokaryotic cells, is the genes continuous or discontinuous for both

eukaryotes: usually discontinuous (interrupted by introns)

prokaryotic cells: usually continuous (lack introns)

what is genetic code and what are they key features of it and explain

genetic code is the set of rules by which information encoded in the DNA is translated into proteins

-linear: DNA is arranged in straight lines

-triplet: bases are found in triplets called codons, 1 codon is the code for one amino acid

-non-overlapping: the codons are kept seperate

-degenerate: more than one codon can code for the same amino acid (64 combination of bases but only 20 amino acids)

-unambiguous: each codon always codes for the same amino acid

-universal: all living organisms have the same codons and amino acids

what are the two main functions of DNA

-protein synthesis

-replication

what are the three proposed models of DNA replication and what do each mean

1.Conservative replication

-original remain intact and a completely new model is made from scratch

2.Dispersive replication

-DNA strands are a mix of old and new segments so each strand contains scattered pieces of original and new DNA

3.Semi-conservative replication (supported by evidence)

-each new DNA molecule contains one original strand and one newly synthesised strand

Describe the process of semi-conservative replication

1.original DNA (double helix) held together by hydrogen bonds

2.the enzyme DNA helicase breaks apart the hydrogen bonds between the bases which makes DNA split into two separate strands

3.the free nucleotides in the nucleoplasm join to their complementary base via hydrogen bonds

4.the hydrogen bond alone is not strong enough so the enzyme DNA polymerase joins the new nucleotides together with phosphodiester bonds to create a new sugar-phosphate backbone

5. this creates two identical DNA molecules with one strand from each DNA being from the orginal

describe the experiment to prove semi-conservative replication and explain the results and why it disproved the other methods

1.they grew E. coli bacteria in a medium containing heavy nitrogen (N15) which made DNA denser than normal

2.then, they moved the bacteria to a medium with light nitrogen (N14) and allowed them to replicate

RESULTS

3.after one round of replication, the DNA was of intermediate density (this ruled out conservative since by now it would have shown one light and one heavy)

4.after two rounds they saw two bands, one light and one intermediate (rules out dispersive which would have shown only intermediate bands even after multiple rounds)

describe the first step of protein synthesis

Transcription: DNA to mRNA

takes place in nucleus and involves copying a gene from DNA into mRNA

1.DNA helicase breaks hydrogen bond between base pairs, unwinding the double helix and exposing the template strand

2.RNA polymerase binds to the template strand and brings free nucleotides (U instead of T) following the rules of complementary base pairings and joins them with phophodiester bonds

3. RNA polymerase continues to the end of the template strand (til it reaches a stop codon) which leaves the molecule called pre-mRNA

   1. post-transcriptional modification removes the introns, producing functional mRNA that can leave the nucleus

describe the second step of protein synthesis

Translation: mRNA to protein

translations occur in the cytoplasm at the ribosome and involves converting the mRNA code into a sequence of amino acids to form a polypeptide 

1.initiation: mRNA leaves nuclear pore, goes to ribosome, ribosome attahes to start codon at one end of the mRNA molecule. The first tRNA with anticodon matches to the codon of the mRNA and join with hydrogen bonds

2.elongation: two tRNA, the two amino acids are close enough for peptide bond. The first tRNA leaves the ribsome leaving the amino acid and the next tRNA binds

3.termination: process continues until a stop codon is reached

-stop codon is a codon which does not have a complementary anti-codon so no amino acid is brought.

4.polypeptide goes to golgi body