Lecture 5 - Part 2 - Transcription and translation Flashcards
Why look at transcription and translation
It explains how nucleic acids construct proteins
How many chromosomes does each human have
46 chromosomes ( 23 pairs )
What is a chromosome and how is it formed
- ## DNA, wrapped up and packaged, wound around other proteins into these X shaped parcels and twisted/further folded
What are histones
Proteins that condense/ coil and structure the DNA of eukaryotic cell nuclei into units called nucleosomes
What are the core histones
H2A, H2B, H3 and H4 `
What does the histone octamer consist of
2 copies of each histone protein
What is the nucleosome core formed of
Two H2A-H2B dimers and a
H3-H4 tetramer
How is nucleosome formed and what does each one consist of
DNA coils twice aroundtheoctamer
8 histone proteins
What anchors nucleosome together
Histone H1
What are nucleotides
Building blocks of nucleic acids
What is the structure of nucleotide
-Nitrogenous base
-5C sugar can be..
Ribose = RNA
Deoxyribose = DNA
-Phosphate group
What gives the structral element of nucleotide
Sugar and phosphate
What does base do
Encodes genetic information
What’s the sugar for DNA
Deoxyribose
What’s the sugar for RNA
Ribose
What is the 5 carbon sugar and how are carbon atoms labelled
Pentose ring
Carbon atoms in pentose ring labelled 1-5 clockwise from Oxygen
How is ribose and deoxyribose struucturally different
For Ribose -OH group at 2’ postiion
What determines genetic information
Sequence of bases on DNA
What carbon number is phosphate group attached to
5th carbon
What are the 4 bases in DNA
Adenine (A)
Thymine (T)
Guanine (G)
Cytosine (C)
What are bases classed as
Purines or Pyrimadines
Which bases are Purines
Adenine and guanine
Which bases are Pyrimadines
cytosine and thymine
How many interlocking nitrogen-containing rings does purine contain
Two
How many interlocking nitrogen-containing rings does pyramidine contain
One
What carbon number are bases joined to sugar
C1
What bond is formed between phosphate group and ribose sugar
Phosphodiester bond
How are DNA bases on strands held together
Hydrogen bonds
Which bases are complementary
A + T
C + G
How many hydrogen bond between A + T
2
How many hydrogen bond between C + G
3
Properties of the DNA double Helix
- Two helical polynucleotide chains are coiled around a common axis
- The chains run in opposite directions – antiparallel
- Complementary bases are held together by hydrogen bonds on the inside
- Planes of the Bases are at 90° to axis
- A phosphate-deoxyribose polymer composes the outside backbone of the DNA = phosphodiester bonds
- Nitrogenous bases are covalently bonded to the 1’ carbon of the deoxyribose
- The individual hydrogen bonds are weak but the large number of them confer stability
Is all DNA contained within chromosomes
No
What is independent in terms of DNA
Mitochondria
They contain their own DNA which encode the mitochondrial proteins and some ribosomal RNA.
How many genes does mitochondria contain
37
Essential for normal mitochondrial function
Uses of genes in mitochondria
- Direct the synthesis of enzymes involved in oxidative phosphorylation (ATP production)
- Synthesis of transfer RNA (tRNA)
- Synthesis of ribosomal RNA (rRNA)
- These RNA’s help assemble amino acids into functioning proteins
How does our genetic code translate into what we are
By transcription and translation
Summary of transcription and translation
The genetic code from DNA is ‘copied’ (transcribed) into shorter sequences (RNA), which are then ‘read’ (translated) by a ribosome which generates a sequence of amino acids, the chains that form proteins.
What is RNA
Sequence of nucleotides
How is RNA different from DNA
- Ribose sugar rather than deoxyribose
- RNA is single stranded
- Thymine is substituted for Uracil
What base does Uracil replace
Thymine
Cytosine and Uracil - pyramidine - bases joined to C1 of ribose sugar
Transcription and translation flow diagram
DNA - mRNA - Polypeptide
What is transcription
The production of messenger RNA (mRNA) by the enzyme RNA polymerase, and the processing of the resulting mRNA molecule.
What are the 4 steps of Transcription
Initiation.
Elongation.
Termination.
Processing.
Transcription - Initiation
The DNA molecule unwinds and separates to form a smallopen complex. RNA polymerase (enzyme) binds to the promoter of thetemplate strand.
What does transcription factors do
Bind to the TBP which binds to TATA box (promoter)
Transcription - elongation
RNA polymerase II moves along the template strand, synthesising an mRNA molecule
Phosphate Group - Joins 3’ to 5’ Carbon with a Phosphodiester bond
Transcription - Termination
Addition of additional adenine nucleotides at the 3’ of the RNA transcript (a process referred to aspolyadenylation). Creates the poly (A) tail
- Gets to end of gene that it wants to read
- Stops reading gene and adds a load of adenine’s ( poly - A - tail to the end of RNA - polyadenylation
What’s polyadenylation
Addition of adenine nucleotides at the 3’ of the RNA transcript
Transcription - Processing
- RNA splicing removes Introns
- mRNA) is produced, this can now leave the nucleus through nuclear pores
What are genes composed of
Introns and exons
What are introns
non-coding sequences - not essential for making protein
What are exons
Coding sequences - are expressed - produce proteins
What does splicing do
Remove introns - non coding regions from RNA and seal blocks together
What’s translation
mRNA that has left the Nucleus is used as a TEMPLATE to assemble a chain of amino acids (polypeptide) with a specific sequence.
What 2 components does translation require
- Ribosomes
- tRNA
What are 4 steps of translation
Initiation.
Elongation.
Termination.
Post-translation processing of the protein
What does translation involve
- Conversion of the nucleotide sequence of mRNA into an amino acid sequence of a protein
What is ribosome made of
65% rRNA and 35% protein
Where places are ribosome found
Nuclear envelope
R.E.R
Free floating in cytosol
Function of ribosomes in translation
- Catalyse the assembly of protein chains (they’re enzymes)
- Read mRNA sequences, and bind tRNA which are bound in turn to an amino acid.
- Place amino acids next to each other in a sequence that will form the protein read from the mRNA code. You
What do ribosomes consist of
Large and small subunits
What do ribosomes have
Binding site for mRNA and 3 binding sites for tRNA
-Combination of R groups sticking out from protein creates environment with 3 specific pockets which will recruit something in, bind to it and pass onto next pocket
Function/role of tRNA in translation
Helps decode mRNA strand
functioning at the binding sites in ribosomes during translation
What are proteins built from
Amino acids, specified by 3 nucleotide mRNA sequences called codons
What does each codon represent
A particular amino acid and each codon is recognised by specific tRNA
Structure of tRNA
- 3 hairpin loops
- One of these hairpin loops contains a sequence – the anticodon – complimentary to the mRNA codon
- Each tRNA is covalently linked to its corresponding amino acid
What happens when tRNA recognises and binds to its corresponding codon in the ribosome
The tRNA transfers the appropriate amino acid to the end of the growing amino acid chain
What do tRNA and ribosome do
Continue to decode the mRNA molecule until the entire sequence is translated into a protein
Translation - Initiation
- The small ribosome subunit binds at the 5’ end of the mRNA molecule and moves in a 3’ direction.
- It keep moving until it reads a start codon (AUG).
- It then forms a complex with the large unit of the ribosome complex and recruits a tRNA.
Trancription - Elongation
- Following codons of the mRNA chain determine which tRNA molecule next is recruited into the ribosome. This enters binding site A as the first tRNA moves into site P.
- A new peptide bond is formed between amino acids at other end of tRNAs
- The small subunit moves a distance of a codon along the mRNA chain ejecting the spent tRNA molecule
- The next tRNA molecule binds to the A-site on the ribosome
- Steps continue and create a polypeptide
Translation - Termination
- vTranslation in terminated when the ribosomal complex reads a stop codon (either UAA, UAG, UGA).
- This codon binds a release factor and results in hydrolysis of the last amino acid (–COOH) when the ribosomal release factor is read
- The release factor disconnects the polypeptide from the tRNA in the P-site
- The ribsome dissociates into its two separate subunits
Gene expression
- Multiple identical RNA copies can be made from the same gene
- Each RNA molecule can direct the synthesis of many identical protein molecules
- Each gene can be transcribed and translated with different efficiency
- RNA polymerase requires transcription factors - genes are up or down regulated by transcription factors
- Transcription and translation are regulated
Controlling gene expression - Transcription control
- The most common type of genetic regulation
- Turning on and off of mRNA formation
- The rate at which DNA is being read and turned into RNA
- Regulated by availability of transcription factors
Controlling gene expression - Post - Transcription control
Regulation of the processing of a pre-mRNA into a mature mRNA
- Regulation of splicing enzymes
Controlling gene expression - Translational Control
Regulation of the rate of Initiation - availability of ribosomes, tRNA - limit how much RNA into protein
Controlling gene expression - Post Translational Control
Regulation of the modification of an immature or inactive protein to form an active protein
i.e. how it processes through golgi and modified with lipids and sugars
What happens to genetic material ( chain )
It’s split up into 20,000 different regions - each one = gene - contains genetic code to make one protein
What does TATA box represent
Binding/promoter region of genetic code
What do transcription factors do
Recruit enzyme - RNA polymerase II
What does RNA polymerase II do
- Opens up DNA and starts transcription process - starts reading of genetic code and produce RNA chain
- Binds to the promoter of thetemplate strand
What does RNA polymerase II do in elongation
Unwinds double helix and reads 1 chain of DNA and recruits in free floating nucleotides and pieces in complementary base. e.g. C and G
What happens once the nitrogenous base has binded to its complementary base
Creates a chain of RNA which is complementary to DNA sequence
How are RNA’s binded together
Condensation reaction
What does splicing produce
mRNA - template strand
What does mRNA bind with during translation
Ribosome
What is mRNA used for in translation
A template to produce protein
What does ribosome recruit
tRNA
What is gene
Sequence of bases
How are bases read
In groups of 3 - codon - triplet
What are triplets of bases referred to in mRNA
Codons
What is each codon specific for
Certain amino acid
Where is RNA produced
Nucleus
What creates the hairpin loops in tRNA
Hydrogen bonding
What is anticodon
Sequence of 3 bases in a row which then specific sequence.
How many different types of tRNA’s
64
What is start codon for every protein in body
AUG
What happens when start codon is read
Ribosome brings in tRNA and starts translation
When does termination happen
When there’s a stop codon
What do stop codon’s represent
Not amino acid, instead its represents tRNA not bind to amino acid
What is post translation processing of protein
Can be modified afterwards
Go into golgi apparatus - add sugars
Why regulate gene expression ( transcription and translation)
Don’t need every protein identified in genetic material being produced at the same rate all the time - inefficient
What is one way of regulating gene expression
Binding of transcription factors - change rate at which RNA is being produced and therefore rate at which protein is being produced from that
How are transcription factors activated
- Cleaving off region
Phosphorylating/dephosphorylating
What happens when transcription factors are active
Migrate into nucleus and bind to DNA and initiate transcription
