9- Genes and Protein synthesis

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relevant topics= pack 21 + 22

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55 Terms

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What is a gene?

a section/ sequence of DNA that codes for 1 polypeptide, and in turn determine the nature and development of organisms

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What is an allele?

a different form of a gene

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What is the fixed position a gene occupies called?

a locus

<p>a <strong>locus</strong> </p>
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What is a pair of chromosomes called?

homologous pair

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What genotype is BB?

homozygous (dominant)

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What genotype is Bb?

heterozygous

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What genotype is bb?

homozygous (recessive)

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What does DNA carry?

the genetic code to allow the cell to make proteins

  • as enzymes are proteins, and enzymes control all the chemical processes going on inside cells, proteins are vital to a cell’s functions

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What is the only difference between DNA strands?

  • length

  • sequence of bases

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What is a triplet code?

3 base code for 1 amino acid

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What are the 3 important features of genetic code?

  • non-overlapping

  • degenerate

  • universal

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What does it mean if the genetic code is non-overlapping?

each base is part of only 1 triplet

<p>each base is part of only 1 triplet</p>
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What would happen in an overlapping code?

each base would be part of 3 triplets

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What does it mean if the genetic code is degenerate?

some amino acids are coded by for more than one triplet

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Why is the genetic code degenerate?

there are 64 different triplet codes but only 20 amino acids

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What does it mean if the genetic code is universal?

a given triplet specifies the same amino acid in all organisms

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How does the gene code informationWhat does it mean if the genetic code is non-overlapping?

the specific sequence of bases on 1 strand of DNA controls the sequence of amino acids in polypeptide chains/ proteins (e.g. primary structure) that are made by a cells ribosomes, and therefore the tertiary structure and function of that protein

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What does RNA stand for?

ribonucleic acid

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What are the 3 main types of RNA?

  • ribosomal RNA

  • messenger RNA

  • transfer RNA

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What is ribosomal RNA?

rRNA + proteins= a ribosome

  • site of mRNA translation and protein synthesis

  • rRNA is coded for by numerous genes in many different chromosomes

<p>rRNA + proteins= a ribosome</p><ul><li><p>site of mRNA translation and protein synthesis</p></li><li><p>rRNA is coded for by numerous genes in many different chromosomes </p></li></ul><p></p>
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What is messenger RNA?

  • formed by transcription in the nucleus

  • is complementary to the DNA of its base sequence

  • molecules consist of thousands of nucleotides in a single linear strand

  • amino acid is coded by a triplet of bases on mRNA called a codon

  • has many unpaired bases so is easily broken down in cytoplasm- only needs to exist temporarily until protein is manufactured

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What is transfer RNA?

  • shortest RNA molecule- made from around 80 nucleotides

  • single strand which folds back on itself

  • forms hydrogen bonds within complementary sections so causes the folding

  • not linear

  • has an anticodon

  • longer end holds the amino acid

<ul><li><p><strong>shortest</strong> RNA molecule- made from around 80 nucleotides </p></li><li><p><strong>single strand which folds back on itself</strong></p></li><li><p>forms <strong>hydrogen bonds</strong> within complementary sections so causes the folding</p></li><li><p>not linear </p></li><li><p>has an <strong>anticodon</strong></p></li><li><p>longer end holds the amino acid</p></li></ul><p></p>
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What is the role of the many hydrogen bonds in tRNA?

help stabilise the molecule

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Tell me about the end of the chain that attaches to the amino acid in tRNA

  • each carry a single specific amino acid

  • at the base of the tRNA molecule is a sequence of 3 bases called the anticodon

  • in RNA, thymine is replaced by uracil

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What is non-coding DNA?

  • between genes

  • doesn’t code for protein synthesis

  • contains multiple repeats called Variable Number Tandem Repeats (VNTRs) and are important in genetic fingerprinting

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What are the non-coding sections called?

introns

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What are the coding sections called?

exons

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Give differences between DNA structure in prokaryotes and eukaryotes

PROKARYOTE DNA

  • circular

  • no protein (histones associated)

  • shorter

  • no introns

  • free within cytoplasm (not on MS)

EUKARYOTE DNA

  • linear

  • associated with protein (histones)

  • longer

  • has introns

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What is the genome?

the complete set of genes in a cell

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What is the proteome?

the full range of proteins that a cell is able to produce

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Both pancreas and liver cells contain the gene that codes for the insulin protein. However, only pancreas cells produce insulin.

Would the genome of a pancreas cell and liver cell be the same?

yes as contain identical genes due to mitosis

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Both pancreas and liver cells contain the gene that codes for the insulin protein. However, only pancreas cells produce insulin.

Why would the proteomes be different?

genes to make some proteins may be switched off so the cell never produces that protein e.g. in the liver cells, insulin would be part of the proteome of the pancreatic cell but not the liver cell

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What is the order of protein synthesis?

DNA—transcription—> pre-mRNA—splicing—> mRNA—translation—> polypeptide chain (protein)

<p>DNA—<strong>transcription</strong>—&gt; pre-mRNA—<strong>splicing</strong>—&gt; mRNA—<strong>translation</strong>—&gt; polypeptide chain (protein)</p>
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What is transcription?

  • takes place in the nucleus

  • involves the formation of pre-mRNA

  • has a complementary sequence of bases to the DNA

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What is RNA processing?

  • takes place in the nucleus

  • non-functioning sequences of bases are spliced from pre-mRNA to form mRNA

  • mRNA then leaves the nucleus via nuclear pores and attaches to a ribosome

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What is translation?

  • occurs on ribosomes

  • involves translation of mRNA into a specific sequence of amino acids to form a polypeptide

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What is the 5 marker for transcripton?

  • the hydrogen bonds between DNA bases are broken which separates the 2 strands of DNA

  • 1 strand of the DNA acts as the template strand upon which pre-mRNA is built

  • free RNA nucleotides are found in the nucleoplasm. They are attracted to exposed DNA bases on the DNA template strand and align by complementary base pairing

  • uracil= adenine, guanine= cytosine

  • RNA polymerase join RNA nucleotides together to make an RNA polynucleotide chain via phosphodiester bonds

  • introns are removed from the pre-mRNA and the exons spliced back together

<ul><li><p>the <strong>hydrogen bonds</strong> between DNA bases are <strong>broken</strong> which <strong>separates the 2 strands of DNA</strong></p></li><li><p><strong>1 strand</strong> of the DNA acts as the <strong>template strand</strong> upon which pre-mRNA is built </p></li><li><p><strong>free RNA nucleotides </strong>are found in the nucleoplasm. They are <strong>attracted to exposed DNA bases</strong> on the DNA template strand and <strong>align by complementary base pairing</strong> </p></li><li><p>uracil= adenine, guanine= cytosine</p></li><li><p><strong>RNA polymerase join</strong> RNA nucleotides together to make an RNA polynucleotide chain via <strong>phosphodiester bonds</strong></p></li><li><p><strong>introns are removed</strong> from the pre-mRNA and the <strong>exons spliced back together </strong></p></li></ul><p></p>
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What is splicing of pre-mRNA? (eukaryotes only)

  • DNA is made from sections called exons and introns

  • exons are expressed to produce proteins

  • in pre-mRNA, the introns are removed by enzymes before the mRNA moves into the cytoplasm

  • remaining exons are joined together= splicing

  • mRNA molecules leave the nucleus through the nuclear pores

<ul><li><p>DNA is made from sections called exons and introns</p></li><li><p>exons are expressed to produce proteins</p></li><li><p>in pre-mRNA, the <strong>introns are removed by enzymes </strong>before the mRNA moves into the cytoplasm</p></li><li><p>remaining <strong>exons are joined together</strong>= <strong>splicing</strong></p></li><li><p>mRNA molecules leave the nucleus through the nuclear pores</p></li></ul><p></p>
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Tell me about protein synthesis in prokaryotes

  • transcription—> translation

  • do not contain non-coding sections, therefore do not produce pre-mRNA that requires splicing

<ul><li><p>transcription—&gt; translation</p></li><li><p>do not contain non-coding sections, therefore do <strong>not </strong>produce pre-mRNA that requires splicing</p></li></ul><p></p>
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What is transcription in a prokaryote?

  • takes place in cytoplasm

  • involves the formation of functional mRNA that is a complementary sequence of bases to the DNA

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What is translation in a prokaryote?

  • occurs on ribosomes

  • involves the translation of the mRNA message into a specific sequence of amino acids to form a polypeptide chain

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How can you work out what amino acid the mRNA codon is coding for?

the codon dictionary

<p>the codon dictionary </p>
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What is the start codon/ amino acid?

AUG= Methionine (Met)

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How many stop codons are there?

3

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What are the stop mRNA codons?

  • UAA

  • UAG

  • UGA

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How many bases of the codon code for the amino acid?

the first 2 of the triplet

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Why don’t all the bases code for a specific amino acid?

reduces the chance that a change in the bases will alter the function of the polypeptide

48
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What is the 5 marker for translation?

  • mRNA attaches to ribosomes

  • tRNA anticodons bind to mRNA codons by complementary base pairing

  • each tRNA brings a specific amino acid

  • 2 tRNA molecules are held together at a ribosomes at any one time

  • a peptide bond forms between adjacent amino acids. This requires the use of ATP

  • tRNA molecules are released after their amino acids have been joined to the growing polypeptide chain

  • the ribosome moves along the mRNA forming the polypeptide until a stop codon is reached, at which point the ribosome and mRNA dissociate

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What is similar to the DNA triplet code?

the tRNA anticodon

  • TTC= UUC

  • AGG= AGG

  • GCC= GCC

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What does the mRNA codon code for?

the amino acid

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What are the comparison points for DNA?

  • double polynucleotide chain

  • longest molecule of the 3

  • double helix shape

  • pentose sugar is deoxyribose

  • bases found are A T C G

  • found mostly in the nucleus (doesn’t want to get damaged)

  • chemically stable

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What are the comparison points for mRNA?

  • single polypeptide chain

  • shorter than DNA, longer than tRNA

  • single linear strand (single helix)

  • pentose sugar is ribose

  • bases found are A U C G

  • manufactured in nucleus but found throughout the cell

  • less stable than DNA or tRNA. Usually broken down within a few days

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What are the comparison points for tRNA?

  • single polynucleotide chain

  • shortest

  • clover leaf shaped molecule (single strand folded back on itself and forms hydrogen bonds within complementary sections)

  • pentose sugar is ribose

  • bases found are A U C G

  • maufactured in the nucleus but found throughout the cell

  • more stable than mRNA, less stable than DNA (due to H bonds)

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Give an advantage of mRNA being broken down relatively quickly

  • mRNA is used in protein production

  • a protein only needs to be produced when it is needed

  • mRNA breaks down once used and is made again when protein production is required

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Describe how mutations affect the protein

  • different base sequence leads to a different amino acid sequence (primary structure), which leads to bonds forming in different places, so there is a different tertiary structure in the protein coded for by that gene

  • if the protein is an enzyme, the active site will change shape, the substrate will not fit so fewer/ no enzyme-substrate complexes will form