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​

​

​

​

​​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

​

​

​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

Fill in the Blanks

Name the enzyme which moves along the gene and breaks the hydrogen bonds between the bases during the start of transcription

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

Fill in the Blanks

What signals the beginning of the translation?

Fill in the Blanks

What signals the end of the translation?

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

Fill in the Blanks

What holds together the amino acids and forms the protein>

​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​

​

​

Fill in the Blanks

The codon that signals the beginning of the Translation

Fill in the Blanks

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

Fill in the Blanks

The codon that signals the end of the Translation

Fill in the Blanks

The introns are removed and the exons are joined together during which process?

Fill in the Blanks

Unit of polypeptide structure

Fill in the Blanks

Sequence of three bases on tRNA that specifies an amino acid

Fill in the Blanks

Sequence of three bases on mRNA that specifies an amino acid

Fill in the Blanks

Which process includes a transcription and a translation phase

Fill in the Blanks

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

Fill in the Blanks

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

Fill in the Blanks

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

Fill in the Blanks

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

Fill in the Blanks

Copying of a DNA sequence to make a primary transcript

Fill in the Blanks

Production of a polypeptide using instructions from mRNA​

​​END OF KEY AREA