Name given to the mixture of DNA proteins and RNA that package DNA within the nucleus Divided between heterochromatin (condensed) and euchromatic (extended) forms

Storing and using genetic information Flashcards by Rachel Hughes

Define phenotype

Outward, physical manifestation of organism

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Define genotype

Full hereditary information of organism (even if not expressed)

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What is a nucleotide made up of?

o 2’ deoxyribose sugar
o Base
o Phosphate group

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Describe the structure of DNA

Double stranded helix
The bases are arranged in the centre of the helix, bound on the outside by the sugar-phosphate backbone.
There are 10 bases for every full turn of the helix.
These nucleotides connect using carbons 3 and 5 on the pentose sugars.
The polynucleotide chains run anti-parallel to one another – that is one runs 5’ to 3’ from the top of the helix in the picture, while the other runs 3’ to 5’.
The way the helix is wound results in a major and a minor groove – this is important for the interaction of proteins with the DNA molecule – many binding sites are located in the major groove.
The double helix is also right-handed and spirals in a clockwise (right-handed) direction.

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Describe complementary base pairing

Complementary base pairing refers to the structural pairing of nucleotide bases in deoxyribonucleic acid, which is commonly known as DNA
• Adenine – Thymine (Uracil in RNA)
• Cytosine - Guanine

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Describe in outline the post-transcriptional processing of RNA.

In eukaryotes, a synthesized RNA transcript may undergo a number of levels of processing known as post-transcriptional modifications. In the case of messenger RNA, modification is necessary to convert pre-mRNA into a mature mRNA that is ready for protein translation. One such modification is splicing.

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Describe alternative splicing and its function

• Alternative splicing is a process by which the exons of the RNA produced by transcription of a gene (a primary gene transcript or pre-mRNA) are reconnected in multiple ways during RNA splicing. The resulting different mRNAs may be translated into different protein isoforms; thus, a single gene may code for multiple proteins.

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Describe chromatin

Name given to the mixture of DNA proteins and RNA that package DNA within the nucleus
Divided between heterochromatin (condensed) and euchromatic (extended) forms

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How can you distinguish between heterochromatin and euchromatin?

Chromatin is found in two varieties: euchromatin and heterochromatin. Originally, the two forms were distinguished cytologically by how intensely they stained – the euchromatin is less intense, while heterochromatin stains intensely, indicating tighter packing.

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Which processes require the two strands of DNA to be separated?

DNA transcription

DNA replication

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What are the two major mechanisms that unwind DNA?

o Histones enzymatically modified

o Histones displaced by chromatin remodelling complexes

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What are the stages of mitosis?

Interphase
Prophase
Prometaphase
Metaphase
Anaphase
Telophase
Cytokinesis

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What does mitosis produce?

Two daughter cells identical to the parent cell

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What happens during interphase?

Chromsomes duplicate and the copies remain attached to each other

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What happens during prophase?

Chromosome condense and become visible in the nucleus. Spindles start to form in the cytoplasm.

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What happens during prometaphase?

Nuclear membrane breaks apart and the spindle starts to interact with the chromosomes

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What happens during metaphase?

The copied chromosomes align in the middle of the spindle

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What happens during anaphase?

Chromsomes separate into two genetically identical groups and move to opposite ends of each spindle

What happens during telophase?

Nuclear membranes form around each set of chromosomes.The chromosomes begin to spread out and the spindle begins to break down,

What happens during cytokinesis?

The cells split into two daughter cells, each with the same number of chromosomes as the parent. In humans, such cells have 23 pairs of chromosomes and are called diploid.

Describe DNA replication

DNA replication is Semi-conservative and Bi-directional. This means that one half of each DNA molecule is old, and the other is new, and the strands are created in opposite directions.
DNA Helicase unzips the double helix by breaking H bonds.
Then new nucleotides are added in using DNA Polymerase, which builds the new DNA strand using complementary base pairing.
The new strand is formed in the C’5 to C’3 direction.
Another Polymerase enzyme is responsible for copying off the other template strand, but it forms discontinuous fragments (okazaki fragments)which are then connected by DNA ligase.

When are chromosomes most compact and visible during mitosis?

Metaphase

What % of the genome codes for proteins?

<2%

Wha % of the genome is made up of repeated sequences?

50%

Define exons and introns

* Exons = Coding Regions | * Introns = Non-coding Regions

What is the genetic code?

* Describes how base sequences are converted into amino acids * Each set of 3 bases is called a codon * Each codon specifies a particular amino acid

How many codons are there in the human genome?

64 (4^4)

What is genetic redundancy?

The number of codons is greater than the number of amino acids. With the exception of methionine and tryptophan they are all encoded by more than one codon.

What are genetic synonyms?

Codons that refer to the same amino acid are called synonyms and tend to be very similar.

What is the wobble position?

Variations between synonyms tend to occur at the third base of the codon – the wobble position.

Whats the benefit of genetic redundancy?

This degeneracy minimises the effect of genetic mutations in order that alterations to the base sequences are less likely to alter the protein being coded for. This prevents any alteration in protein structure and hence function.

What amino acid is the initiation codon?

Methionine

What mutation is associated with sickle cell anaemia?

* A mutated Haemoglobin gene causes Sickle Cell Anaemia. * In the mutant hemoglobin a hydrophilic glutamate (Glu) is substituted by the hydrophobic valine (Val), (GAA or GAG becomes GUA or GUG)

What is RNA used for?

Protein synthesis

Describe the open reading frame

A set of codons runs continuously and is bound by a start/initiation codon and a termination codon – this is known as the open reading frame and is used to identify DNA which encodes protein sequences in genome sequencing projects

What determines the reading frame of an RNA sequence?

Initiation codon

Whats the major role of tRNA?

Major role is to translate mRNA sequence into amino acid sequence

Describe how a base sequence of DNA is transcribed into a base sequence in RNA.

o Methionine only has one possible Codon sequence. It acts as the Initiation Codon and tells enzymes where to begin the transcription of RNA. o From there, the sequence is read in Codons until the Termination Codon is reached, which tells the enzymes to stop transcribing. o Once this has occurred, the sequence copied is spliced and the junk sections of RNA called “Exons” are removed, leaving the Introns., and producing a strand of Messenger RNA (mRNA). During this phase, the initial order of the entrons can be mixed up. i.e. “1-2-3-4” can be rearranged to make “1-2-4”, “1-3-4” or “1-2-3-4”. o Once the mRNA has been produced, a cap is added to the ‘5 end and a tail is added to the ‘3 end, to protect it from being broken down by other enzymes

Describe the translation of mRNA

o Translation occurs in the endoplasmic reticulum o To start off, a small ribosomal subunit attaches to the mRNA molecule. At the same time, a specific tRNA molecule carrying methionine binds to the corresponding section of the mRNA. Finally, the large unit of the ribosome joins the smaller one and the tRNA, and the tRNA occupies the P section of the binding sites. o Once another tRNA comes along carrying the correct amino acid for the next section of mRNA, it binds to the A site. o As the ribosome moves along, the tRNA in the P site leaves, and the one in the A site takes its place, and the amino acid it was carrying. o This sequence continues, and the amino acid chain grows, until a termination sequence is reached, upon which, the polypeptide chain is released and the ribosome splits into its sub units again.

What is the function of mRNA?

Carries information from the nucleus to the cytoplasm for protein synthesis.

What is the function of tRNA?

* Major role is to translate mRNA sequence into amino acid sequence * Acts as an adaptor molecule between the coded amino acid and the mRNA

What is rRNA?

* Component of ribosome * rRNA molecules are produced in nucleus * Transported to cytoplasm where they combine with proteins to form a ribosome * Short half life, very susceptible to enzyme degradation, protects stocks and prevents excessive protein formation

What is a polysome?

Several ribosomes can translate mRNA at one time to make numerous copies of a protein, creating what is known as a polysome