Genetics Core Content

DNA bases

Adenine, Thymine, Guanine, Cytosine

Purine bases

double ring bases: adenine + guanine

Pyrimidine bases

Single ring bases: thymine, cytosine + uracil

RNA bases

adenine, Uracil, guanine, cytosine

3 Parts of a nucleotide

nitrogenous base, phosphate group, pentose sugar

RNA pentose sugar

Ribose

DNA Pentose sugar

deoxyribose

what bonds form between nucleotides in polynucleotides

phosphoidester bonds

what type of reaction is phosphodiester bond formation?

condensation reaction

how can phosphodiester bonds be broken and what type of reaction is the break?

broken by adding back water- hydrolysis reaction

Structure of DNA

2 antiparallel polynucleotides held together by H bonds between complementary base pairs, double helix

DNA complementary base pairs

thymine + adenine, Guanine + Cytosine

how many H bonds in A+T and C+G respectively

2 and 3

how is RNA different from DNA structure?

single shorter polynucleotide strand found in cytoplasm instead of nucleus

DNA replication

all of the DNA is copied for cell division

What is the role of DNA helicase in DNA replication?

DNA helicase enzyme attaches and breaks hydrogen bonds.

What does DNA polymerase do during DNA replication?

gets the complementary active nucleotide for H bonding with exposed DNA bases+ forms new phosphodiester bonds

activated nucleotides

Nucleotides with extra phosphate groups, seperated + held together by H bonds

3 Prime polynucleotide end and its function in transcription + translation

free hydroxyl group on 3 carbon end of pentose sugar- growing end of RNA strand in transcription + regulates mRNA stability in translation

5 prime polynucleotide end and its function in transcription + translation

free phosphate group on 5 carbon end of pentose sugar- start point for RNA polymerase in transcription and acts as entry point for ribosome during translation before it binds at AUG start codon

which direction can DNA polymerase copy

growing strand going from 5' to 3'

how does the 3'-5' strand form in DNA replication

formed as series of short okazaki fragments joined by DNA ligase

semiconservative replication

each of 2 copies contains 1 original strand + 1 new copy

conservative replication

double helix formed with 2 new strands- none of the original DNA retained

experiment that determined whether DNA replication is semiconservative or conservative

N15 (heavier) DNA cultured in N14 (lighter) growth medium, allowed to replicate once + spun in a centrifuge

Results of experiment that confirmed semiconservative replication

after 1 replication, band in the middle of tube determined one strand of N14+ N15 each

results in nitrogen experiment after 2nd replication in N14 growth medium in semiconservative replication

line higher up the tube

theoretical nitrogen experiment results if conservative replication ocurred

1st replication: one line at top and one at bottom

differences between shape of DNA in the nucleus of prokaryotes + in Eukaryotes

in eukaryotes DNA is linear with free ends compared to circular with no free ends

is DNA longer in prokaryotes or eukaryotes?

Eukaryotes

is DNA wrapped around histone proteins in prokaryotes or Eukaryotes?

Eukaryotes

Chromatin

DNA bound to to histone protein that allows DNA to fit in nucleus

chromatids

one of 2 identical DNA strands that are joined by a centromere point to make up a replicated chromosome

homologous chromosome pairs

Pairs of chromosomes that have the same genes but often different alleles

Transcription

base sequence of a gene is copied into complementary base sequence of a molecule (mRNA)

2 stages of protein synthesis

Transcription + Translation

What do complementary activated RNA nucleotides do during transcription?

They move into place and form hydrogen bonds with bases on exposed nucleotides on one strand.

What role does RNA polymerase play in transcription

joins via phosphodiester bond + copies DNA sequence to pre-mRNA

What happens to RNA polymerase after mRNA is synthesized?

RNA polymerase detaches from DNA.

What structural change occurs to DNA after transcription is complete?

DNA returns to its double helix structure.

Where does mRNA move after it is synthesized?

It moves out to the cytoplasm.

What role does DNA helicase play in transcription

1st stage of transcription- breaks H bonds between 2 DNA strands

where does transcription take place

nucleus

Translation

Process by which mRNA is decoded and a polypeptide is produced

in what format are mRNA nucleotides read during translation

as a series of triplets (genetic code)

Start triplet

determines when to start translating mRNA molecule

stop triplets

3 triplets that determine where translation stops

Codon

each triplet in mRNA

Transfer RNA (tRNA)

bidning site for amino acid + triplet of bases

what happens in translation after mRNA moves to cytoplasm

a subunit of ribosome binds to start triplet containing ribosomal RNA

what does tRNA do in translation?

tRNA attaches to start codon with H bonds forming between base pairs on mRNA + tRNA

what bond forms between amino acids in translation and where does the energy for this bond come from

peptide- energy from ATP

ATP

nucleotide that allows energy to be transferred from glucose in small, useful amounts

Describe bond energy in bond breaking in ATP

small amount of energy required to break last covalent bond in phosphate group but large amount of energy released

what type of reaction is the bond break in ATP and what does it require

hydrolysis reaction that requires water

what is the phosphorylation reaction in ATP

ADP + phosphate are released and cycled back to ATP in respiration/photosynthesis

what happens in translation when the ribosome moves to the next triplet?

1st tRNA molecule released to attatch later

in translation what happens when the ribosome reaches the stop codon

detatches and the polypeptide that has been formed is released

RNA splicing

converts pre-mRNA to functional mRNA

Pre-mRNA

after transcription before introns are removed in splicing

introns

non-coding areas of DNA found within and between genes

exons

coding DNA

gene

section of DNA that encodes the amino acid sequence of polypeptides

what do some genes do instead of coding amino acid sequences for polypeptides?

encode functional RNA molecules like tRNA or rRNA

genome

all of the genes in a cell

substitution mutations

one nucleotide is substituted with another

what does the nucleotide sequence of a gene determine?

the amino acid sequence of a protein

what are mutagens and 3 examples of them?

external factors that cause mutations: ionising radiation, chemicals, viruses

gene mutation

small scale change to DNA in a gene

point mutation

genetic mutation involving a change in a single nucleotide

3 types of point mutations

substitution, insertion deletion

3 possible effects on a protein by a substitution mutation

silent mutation due to degenerate genetic code, change in amino acid, mutated codon is a stop codon

degenerate genetic code

multiple codons code for the same amino acid

frame-shift mutations

insertions and deletions

duplication mutation

1+ nucleotides are duplicated

inversion mutation

group of nucleotides seperated + reattached in the same position in reverse order with no frame shift

chromosome mutations

larger scale mutations that effect chromosomes

chromosomal translocation

part of one chromosome breaks away + joins to other

chromosomal translocation can effect phenotype + cause what?

increased cancer risks, developmental issues, reduced fertillity

Polypeptide

chain of amino acids linked together by peptide bonds

protein

larger molecule formed by 1+ polypeptide chains

Heterochromatin

DNA wound tightly in condensed state that makes chromosomes to be visible

why do heterochromatin 'silence' genes?

RNA polymerase + transcription factors can't access genes so transcription cannot take place

Euchromatin

DNA wrapped loosely around histone proteins so transcription can still take place

how is DNA charged and why?

negatively due to large presence of negative phosphate groups

how are histone proteins charged and how does this allow chromatins to form?

positively allowing attraction with DNA

histone acetylation

adding acetyl group to make histone less positive + convert heterochromatin to euchromatin

deacetylation

removal of acetyl group for heterochromatin to form

DNA methylation

inhibits transcription by triggering histone deacetylation + preventing transcription factors from binding to DNA

Promotor

where RNA polymerase binds to initiate transcription

Epigenome

a way of controlling gene expression through Methylation and Acetylation to regulate transcription

what does the epigenome do?

plays a role in determining phenotype

what impacts the epigenome?

diet, stress, parental involvement

Transcription factors

proteins activated by signals that bind to specific base sequences of DNA in the promotor region

RNA interference

Blocking gene expression by regulating levels of specific proteins

2 types of RNA interference

Small interference RNA's (siRNA's), micro RNA's (miRNA's)

What is the role of the Dicer enzyme in siRNA interference?

Dicer enzyme attaches in the cytoplasm and hydrolyzes double-stranded RNA into shorter fragments

What does RISC stand for in the context of siRNA interference?

RNA induced silencing complex

What happens to each RNA strand upon entering the RISC?

One RNA strand is broken down so RISC contains only single-stranded siRNA that is complementary to specific mRNA

What is the function of RISC in relation to mRNA in siRNA interference?

The enzyme in RISC hydrolyzes mRNA into smaller fragments that are too short for translation