DNA, genes and protein synthesis Flashcards
Gene
Unit of hereditary passed down from a parent to its offspring to determine characteristics
Degenerate code
Different codons specify for same amino acid (e.g. val, gly, ala)
STOP codons
End of a polypeptide chain
Do not code for anything
Exons
Code for a protein
Intron
Non-coding sequences, interrupts gene sequence
How to interpret genetic code on a table
1st base: Column on left
2nd base: Row at top
3rd base: Column on right
How DNA is paired into chromosomes
1) Helix wound around histones
2) It’s fixed in position
3) DNA-histone complex coiled
4) Packed into chromosome
5) DNA condensed into 1 chromosome
6) Forms single molecule of DNA
What are homologous pairs
Literally the X chromosomes make
2 chromosomes in a pair ( I + I = X )
States that one is inherited from mother, and the other from father
Diploid number
Number of chromosome pairs
E.g. - humans have 46
Allele
Alternative forms of a gene
What happens if you change a base sequence
Mutation
Different amino acid sequence leads to production of different polypeptide, different protein
What does mRNA stand for
Messenger RNA
What does messenger rna do
Transfers DNA from nucleus to cytoplasm
Contains coded information to determine the sequence of amino acids (i.e. carries instructions to make proteins)
How does mRNA leave the nucleus and why
Leaves nucleus through nuclear pores
Enters cytoplasm and associates with ribosomes
For protein synthesis
Genome
Complete set of genes in a cell
Proteome
Range of proteins produced by genome
What is rna for
Making proteins
What is RNA made up of
Pentose sugar
Phosphate group
Adenine, guanine, cytosine, uracil
What does mRNA do in the cytoplasm
Associates with ribosomes
And
Acts as a template for protein synthesis
Why is mRNAs structure suited for its function
Contains information for production of amino acids IN THE FORM OF CODONS
What does tRNA stand for
Transfer RNA
Shape of tRNA
Clover leaf
What is a feature of tRNA’s structure for protein synthesis
Top of clover leaf one end comes out more than the other
Amino acids can easily attacg
How does the tRNA know how to bind to which amino acids
Each tRNA is specific to a certain amino acids because of its specific anticodon
What’s an anticodon
Sequence of 3 bases at bottom of clover leaf
What does it mean if the code is degenerate
Amino acid coded by more than one codon
Complementary base pairs RNA
Guanine and cytosine
Adenine and uracil
How proteins are formed in DNA summary
1) DNA provides instructions in form of bases
2) Transcription
3) pre-mRNA spliced into mRNA
4) Translation
Bakery analogy of protein synthesis
OVEN = cell organelles -> manufacture proteins
CAKE = protein -> make many different types
INGREDIENTS = amino acids -> make proteins
TYPE OF CAKE RECIPE = genetic code -> can choose different genetic codes depending on what’s needed
MANY COPIES OF RECIPE BOOK = genome -> contains all information needed for a person
PHOTOCOPY RECIPE = transcription -> copy of DNA
MAKING CAKES = translation -> making proteins using transcription (making cakes using photocopied recipe)
What does transcription and translation do
Transcription = copying DNA
Translation = making proteins
Process of transcription
1) Nucleotide bases exposed by enzyme acting on DNA strand, splitting it into RNA
2) Template strand pairs with complementary nucleotides
3) RNA polymerase moves along strand joining nucleotides by peptide bond
4) DNA strand rejoins behind it
5) Enzyme reachers terminator sequences, detaches and pre-mRNA production is complete
What does splicing in eukaryotic cells form
Splicing of pre-mRNA forms mRNA
What is DNA made up of
Made up of exons that code for proteins and introns
These introns prevent synthesis of a polypeptide
What does splicing do
Removes base sequences corresponding to introns
Functional exons are joined together
Synthesising a polypeptide contains what
mRNA strand along the bottom
Ribosome moves along mRNA strand
tRNA (clover leaf, peg looking shapes)
Amino acids attached ontop of tRNA
Bases attached to tRNA and mRNA
Peptide bonds
Process of forming a polypeptide chain
1) Ribosome attaches at starting codon (first 3 bases on mRNA)
2) tRNA and mRNA’s complementary bases pair up (a and u, g and c)
3) Ribosome moves along, pairing next set of bases
4) 2 amino acids on tRNA join by peptide bond (using enzyme and ATP)
5) Once 3 sets of bases have paired up, first amino acid on tRNA is released forming chain of amino acids. tRNA is free to collect another amino acid (peg)
6) Continues until STOP codon
7) Amino acids form a chain off tRNA
Assembling a protein after polypeptide formation
Polypeptide is coiled or folded into secondary structure
Secondary structure is folded into tertiary structure
Different polypeptide chains link to form quaternary structure
Bond in DNA
Phosphodiester
What is a phosphodiester and hydrogen bond between
Phosphodiester = nucleotides
Hydrogen = bases
Describe two differences between the structure of tRNA and mRNA
tRNA is a clover leaf shape, mRNA is linear
tRNA has hydrogen bonds, mRNA does not
tRNA has anticodon, mRNA has codon
tRNA has amino acid binding site, mRNA does not
Describe and explain difference in structure of mRNA and pre-mRNA
1) mRNA has fewer nucleotides
Pre-mRNA more nucleotides
OR
mRNA has no introns
Pre-mRNA has exons and introns
2) because of splicing
Describe how one amino acid is added to a polypeptide that is being formed at a ribosome during translation
TRNA brings specific amino acid to ribosome
Anticodon binds to codon
Amino acids join by condensation reaction using ATP/amino acids join to form a peptide bond
Describe how mRNA is produced from an exposed template strand of DNA. Do not include DNA helicase or splicing in your answer
Free RNA nucleotides from complementary base pairs
Phosphodiester bond forms
By RNA polymerase
Describe how mRNA is formed by transcription in eukaryotes
1) Hydrogen bonds break between DNA bases
2) One DNA strand acts as a template
3) Free RNA nucleotides align by complementary base pairing
4) Uracil base, pairs with adenine on DNA
5) RNA polymerase joins nucleotides
6) Phosphodiester bonds form
7) Pre-mRNA is splices to form mRNA
Describe how a polypeptide is formed by translation of mRNA
1) Ribosomes attach with mRNA
2) Anticodons bind to complementary codons
3) tRNA brings specific amino acid
4) Amino acids join by peptide bonds
5) Amino acids join using ATP
6) tRNA is released
7) The ribosome moves along the mRNA to form the polypeptide
Describe how mRNA is produced in a plant cell
1) DNA strands separate breaking H bonds
2) One of template strand used to make mRNA
3) Complementary base pairing A and U, T and A, C and G, G and C
4) Nucleotides join by RNA polymerase
5) Pre-mRNA formed
6) Splicing to form mRNA
Describe the role of a ribosome in the production of a polypeptide. DO not include transcription in your answer
1) mRNA binds to ribosome
2) Two codons
3) tRNA binds with anticodons
4) Catalyses formation of peptide bond between amino acids
5) Moves mRNA to next codon (translocation)
