Higher Biology - Unit 1.3

​Unit 1.3

Gene expression

​Genes

• Gene expression is the process of using information from a gene to synthesis a protein

• Genes are expressed to produce proteins which determine the phenotype of an individual

• As well as gene expression, environmental factors such as diet also influence phenotype

​Genotype and Phenotype

• A cells genotype is determined by the sequence of bases in it's genes

• A cells phenotype by the proteins that are synthesised when genes are expressed

​Protein synthesis

​The 2 stages...

​​ Transcription

The synthesis of RNA

from a section of DNA​

​ Translation

The synthesis of a protein

using instructions from mRNA​

​DNA and RNA

The differences between them should be recognized​

​RNA

​There are three different types of RNA:

mRNA Messenger RNA, a linear molecule which carries a copy of the gene to be expressed from the nucleus.

tRNA Transfer RNA has a cloverleaf shape. Made from a single strand of RNA which folds to form an unusual shape due to base pairing.

rRNA Ribosomal RNA and proteins from the ribosome (a structure where protein synthesis takes place).​

Multiple Choice

Genotype

• An individuals alleles for a particular characteristic

• An individuals physical appearance based on the alleles for a particular characteristic

Multiple Choice

Phenotype

• An individuals alleles for a particular characteristic

• An individuals physical appearance based on the alleles for a particular characteristic

Multiple Choice

The synthesis of RNA from a section of DNA

• Transcription

• Translation

• Genotype

• Phenotype

Multiple Choice

The synthesis of a protein using instructions from mRNA

• Translation

• Transcription

• Genotype

• Phenotype

Multiple Select

Select the structural features which apply to DNA

• Double stranded

• Single stranded

• Contains deoxyribose sugar

• Contains ribose sugar

• Has Uracil as one of its bases

Multiple Select

Select the structural features which apply to RNA

• Single stranded

• Double stranded

• Contains uracil as one of its bases

• Contains deoxyribose sugar

• Contains ribose sugar

Multiple Choice

mRNA

• A linear molecule which carries a copy of the gene to be expressed from the nucleus.

• Has a cloverleaf shape. Made from a single strand of RNA which folds to form an unusual shape due to base pairing.

• Proteins from the ribosome (a structure where protein synthesis takes place).

Multiple Choice

tRNA

• A linear molecule which carries a copy of the gene to be expressed from the nucleus.

• Has a cloverleaf shape. Made from a single strand of RNA which folds to form an unusual shape due to base pairing.

• Proteins from the ribosome (a structure where protein synthesis takes place).

Multiple Choice

rRNA

• Proteins from the ribosome (a structure where protein synthesis takes place).

• A linear molecule which carries a copy of the gene to be expressed from the nucleus.

• Has a cloverleaf shape. Made from a single strand of RNA which folds to form an unusual shape due to base pairing.

​​ Transcription

The enzyme RNA polymerase ​moves along the gene unwinding the double helix and breaking the hydrogen bonds between the bases

​1

​Transcription

​2

​RNA polymerase synthesises a primary transcript of mRNA from free nucleotides by complementary base pairing

​Transcription

​3

​RNA polymerase will keep adding nucleotides from the 5' end to the 3' end of the growing mRNA molecule until a specific sequence of nucleotides called a stop codon is reached. A primary mRNA transcript is then formed

​Codons

​Each triplet of bases on the mRNA molecule is called a codon and codes for a specific amino acid.

​

There are 21 amino acids in total. The different combinations of Amino acids makes the different proteins a cell needs​

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​​Splicing

​Prior to the translation in the Ribosome, a technique called splicing occurs in the cytoplasm. Splicing forms a mature mRNA transcript

​​Splicing

Splicing takes place in order to turn a primary ​transcript of mRNA into a mature transcript of mRNA

​

The introns are non coding regions of the DNA and are removed.

Exons are coding regions and are spliced (joined together) and the mature mRNA transcript is formed

​

​

Visual representation ​

​

​"Mature transcript of mRNA"

​Translation

​1

​The mRNA model attaches itself to the ribosome

​Translation

​2

​tRNA transport specific amino acids to the ribosome

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​Each mRNA codon codes for a specific amino acid. The first codon is called a start codon which signals the beginning of the translation. The last codon is called a stop codon which signals the end of the translation

​​During this process, the anti-codons and codons match up to for complementary base pairs. The used tRNA molecules exit the ribosome and collect another specific amino acid

​​Translation

​3

​Peptide bonds form between the adjacent amino acids to form the polypeptide (protein)

​​​The Structure of Proteins

​Proteins have many functions. The function is determined by it's shape, which is determined by the sequence of amino acids.

​

Amino acids are linked by peptide bonds to form polypeptides (proteins), and hydrogen bonds cause the amino acids to fold in repeated patterns​

Multiple Choice

The transcription phase involves...

• The synthesis of RNA from a section of DNA

• The synthesis of a protein using instructions from mRNA

Multiple Choice

The translation phase involves...

• The synthesis of RNA from a section of DNA

• The synthesis of proteins using instructions from mRNA

Multiple Choice

Select the activities of RNA polymerase during the transcription phase of gene expression

• Signals the beginning of the translation

• Breaks the weak hydrogen bonds between the bases

• Synthesises the primary transcript of mRNA

• Removes the introns from the primary transcript to create the mature transcript of mRNA

Multiple Choice

Which of these statements are false?

• RNA is single stranded

• RNA contains uracil instead of Guanine

• tRNA strands contain anti-codons and release amino acids in the ribosome

• The amino acids are connected by peptide bonds which form the proteins

Multiple Choice

Which sequences of DNA stay and go during splicing?

• Introns leave and Exons stay

• Exons leave and Introns stay

• The start and stop codons are reversed

• Introns and exons multiply, and half the exons leave the strand

​List of Terms

​Amino Acid - Unit of polypeptide structure

Anti-codon - Sequence of three bases on tRNA that specifies an amino acid

Codon - Sequence of three bases on mRNA that specifies an amino acid

Exon - Sequence of DNA that codes for part of a protein. They are joined together during splicing

Intron - Sequence of DNA that codes for part of a protein. They are removed during splicing

Gene expression - Transcription followed by the Translation

Primary transcript - Molecule of mRNA made when DNA is transcribed before splicing (Introns and Exons)

Mature transcript - Molecule of mRNA made when DNA is transcribed after splicing (Only Exons)

Peptide bonds - Strong chemical links which join amino acids in the structure of polypeptides

Polypeptides - A short strand of amino acids (a fancy word for protein)

Ribose sugar - Sugar component of RNA nucleotide (the alternative to deoxyribose in a DNA nucleotide)

Start codon - Signals the start of the translation

Stop codon - Signals the end of the translation

Transcription - Copying of a DNA sequence to make a primary transcript

Translation - Production of a polypeptide using instructions from mRNA​

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​​END OF KEY AREA