2.6 & 2.7 & 7.1,7.2, 7.3

Which bases pair up?

A + T, G + C

Outline DNA nucleotide structure in terms of sugar (deoxyribose), base and phosphate

A nucleotide is made of the sugar deoxyribose, a base (which can be either adenine, guanine, cytosine or thymine) and a phosphate group. Below is a representation of a nucleotide.

Discuss the relationship between one gene and one polypeptide.

A polypeptide is formed by amino acids liking together through peptide bonds. There are 20 different amino acids so a wide range of polypeptides are possible. Genes store the information required for making polypeptides. The information is stored in a coded form by the use of triplets of bases which form codons. The sequence of bases in a gene codes for the sequence of amino acids in a polypeptide. The information in the genes is decoded during transcription and translation leading to protein synthesis.

What bond is formed to link nucleotides together?

covalent bond (covalent bond between phosphate group and sugar and between sugar and base)

In DNA the two strands of polymer chains wound together to form _______?

double helix

What is a nucleic acid?

large molecules that are constructed by linking together nucleotides to form a polymer

Pyrimidine

shorter base (T and C)

Purine

longer base (A and G)

What are the 3 parts of a nucleotide?

1. Sugar (consists of 5 carbons and is a pentagon shape) 2. Phosphate Group (the acidic, neg-charged part of the nucleic acid) 3. Base (contains nitrogen and has one or two rings in the structure)

What are the 3 differences between DNA and RNA?

1. The sugar in DNA is deoxyribose and the sugar in RNA is ribose 2. There are 2 polymer strands in DNA (Double-stranded) and only 1 strand in RNA (single-stranded) 3. Uracil is present in RNA instead of Thymine

What needs to be included in a drawing of the structure of DNA?

1. the two strands run parallel to each other 2. all the bases are labeled 3. the complementary pairs are lined up (A+T, G+C) 4. the hydrogen bonds are labeled 5. the covalent bonds are labeled 5. the phosphate group is labeled 6. deoxyribose sugar is labeled 8. the 3' and 5' is labeled

How many hydrogen bonds are between Adenine and Thymine?

2

How many hydrogen bonds are between Guanine and Cytosine?

3

Describe the genetic code in terms of codons composed of triplets of bases.

A triplet of bases (3 bases) forms a codon. Each codon codes for a particular amino acid. Amino acids in turn link to form proteins. Therefore DNA and RNA regulate protein synthesis. The genetic code is the codons within DNA and RNA, composed of triplets of bases which eventually lead to protein synthesis.

What are the 4 bases for DNA?

Adenine, Thymine, Guanine and Cytosine

What are the 4 bases for RNA?

Adenine, Uracil, Guanine and Cytosine

How do we know that A ant T complement each other and G and C complement each other?

Because Chargaff found that the ration of A to T was 1 to 1 and the ration of G to C is 1 to 1.

Outline how DNA nucleotides are linked together by covalent bonds into a single strand.

Below is a diagram showing how nucleotides are linked to one another to form a strand. A covalent bond forms between the sugar of one nucleotide and the phosphate group of another nucleotide.

Explain the significance of complementary base pairing in the conservation of the base sequence of DNA.

Complementary base pairing is very important in the conservation of the base sequence of DNA. This is because adenine always pairs up with thymine and guanine always pairs up with cytosine. As DNA replication is semi-conservative (one old strand an d one new strand make up the new DNA molecules), this complementary base pairing allows the two DNA molecules to be identical to each other as they have the same base sequence. The new strands formed are complementary to their template strands but also identical to the other template. Therefore, complementary base pairing has a big role in the conservation of the base sequence of DNA.

What are the two types of nucleic acid?

DNA and RNA

Compare the structure of RNA and DNA.

DNA and RNA both consist of nucleotides which contain a sugar, a base and a phosphate group. However there are a few differences. Firstly, DNA is composed of a double strand forming a helix whereas RNA is only composed of one strand. Also the sugar in DNA is deoxyribose whereas in RNA it is ribose. Finally, both DNA and RNA have the bases adenine, guanine and cytosine. However DNA also contains thymine which is replaced by uracil in RNA.

Explain how a DNA double helix is formed using complementary base pairing and hydrogen bonds.

DNA is made up of two nucleotide strands. The nucleotides are connected together by covalent bonds within each strand. The sugar of one nucleotide forms a covalent bond with the phosphate group of another. The two strands themselves are connected by hydrogen bonds. The hydrogen bonds are found between the bases of the two strands of nucleotides. Adenine forms hydrogen bonds with thymine whereas guanine forms hydrogen bonds with cytosine. This is called complementary base pairing. Below is a digram showing the molecular structure and bonds within DNA.

Describe the structure of DNA, including the antiparallel strands, 3??5? linkages and hydrogen bonding between purines and pyrimidines.

DNA is made up of two strands. At one end of each strand there is a phosphate group attached to the carbon atom number 5 of the deoxyribose (this indicates the 5' terminal) and at the other end of each strand is a hydroxyl group attached to the carbon atom number 3 of the deoxyribose (this indicates the 3' terminal). The strands run in opposite directions and so we say that they are antiparallel. One strand runs in a 5'-3' direction and the other runs in a 3'-5' direction. Adjacent nucleotides are attached together via a bond between the phosphate group of one nucleotide and the carbon atom number 3 of the deoxyribose of the other nucleotide. The bases of each strand link together via hydrogen bonds. Adenine and Guanine are purines as they have two rings in their molecular structure. Thymine and Cytosine are pyrimidines as they only have one ring in their molecular structure. A purine will link with a pyrimidine. Adenine and thymine link together by forming two hydrogen bonds while Guanine and cytosine link together by forming 3 hydrogen bonds.

Explain DNA replication in terms of unwinding the double helix and separation of the strands by helicase, followed by formation of the new complementary strands by DNA polymerase.

DNA replication is semi-conservative (as both of the DNA molecules produced are formed from an old strand and a new one.) The first stage of DNA replication involves the unwinding of the double strand of DNA (DNA double helix) and separating them by breaking the hydrogen bonds between the bases. This is done by the enzyme helicase. Each separated strand now is a template for the new strands. There are many free nucleotides around the replication fork which then bond to the template strands. The free nucleotides form hydrogen bonds with their complimentary base pairs on the template strand. Adenine will pair up with thymine and guanine will pair up with cytosine. DNA polymerase is the enzyme responsible for this. The new DNA strands then rewind to form a double helix. The replication process has produced a new DNA molecule which is identical to the initial one.

What direction does DNA replication occur?

DNA replication occurs in a 5'→3' direction.

Outline DNA transcription in terms of the formation of an RNA strand complementary to the DNA strand by RNA polymerase.

DNA transcription is the formation of an RNA strand which is complementary to the DNA strand. The first stage of transcription is the uncoiling of the DNA double helix. Then, the free RNA nucleotides start to form an RNA strand by using one of the DNA strands as a template. This is done through complementary base pairing, however in the RNA chain, the base thymine is replaced by uracil. RNA polymerase is the enzyme involved in the formation of the RNA strand and the uncoiling of the double helix. The RNA strand then elongates and then separates from the DNA template. The DNA strands then reform a double helix. The strand of RNA formed is called messenger RNA.

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Eukaryotic RNA needs the removal of introns to form mature mRNA.

Distinguish between unique or single-copy genes and highly repetitive sequences in nuclear DNA.

Not all of the base sequences in DNA are translated. Highly repetitive base sequences are not translated. They consist of sequences of between 5 and 300 bases that may be repeated up to 10 000 times. They constitute 5-45% of eukaryotic DNA. Single-copy genes or unique genes are translated and constitute a surprisingly small proportion of eukaryotic DNA.

Outline the structure of nucleosomes.

Nucleosomes consiste of DNA wrapped around eight histone proteins and held together by another histone protein.

State that nucleosomes help to supercoil chromosomes and help to regulate transcription.

Nucleosomes help to supercoil chromosomes and help regulate transcription.

Outline the structure of ribosomes, including protein and RNA composition, large and small subunits, three tRNA binding sites and mRNA binding sites.

Ribosomes have a particular structure. They are made up of proteins and ribosomal RNA. They have two subunits, one large the other small. On the surface of the ribosome there are three sites to which tRNA can bind to. However not more than two tRNA molecules can bind to the ribosome at one time. Also there is a site on the surface of the ribosome to which mRNA can bind to.

Explain that each tRNA molecule is recognized by a tRNA-activating enzyme that binds a specific amino acid to the tRNA, using ATP for energy.

Summary: Each tRNA activating enzyme recognises a specific tRNA molecule The tRNA molecule is made up of double stranded sections and loops At the 3' end of the tRNA there is the nucleotide sequence CCA to which the amino acid attaches to The different chemical properties and three dimensional structure of each tRNA allows the tRNA-activating enzymes to recognise their specific tRNA Each tRNA enzyme binds a specific amino acid to the tRNA molecule The tRNA-activating enzyme will bind the amino acid to the tRNA with the matching anticodon Energy from ATP is needed during this process

Explain the process of transcription in prokaryotes, including the role of the promoter region, RNA polymerase, nucleoside triphosphates and the terminator.

Summary: RNA polymerase binds to the promoter region This initiates transcription RNA polymerase uncoils the DNA Only one strand is used, the template strand Free nucleoside triphosphates bond to their complementary bases on the template strand Adenine binds to uracil instead of thymine As the nucleoside triphosphates bind they become nucleotides and release energy by losing two phosphate groups The mRNA is built in a 5'→3' direction RNA polymerase forms covalent bonds between the nucleotides and keeps moving along the DNA until it reaches the terminator The terminator signals the RNA polymerase to stop transcription RNA polymerase is released and mRNA separates from the DNA The DNA rewinds

Explain the process of translation, including ribosomes, polysomes, start codons and stop codons.

Summary: The tRNA containing the matching anticodon to the start codon binds to P site of the small subunit of the ribosome The small subunit binds to the 5' end of the mRNA and moves along in a 5'→3' direction until it reaches the start codon The large subunit then binds to the smaller one The next tRNA with the matching anticodon to the next codon on the mRNA binds to the A site The amino acids on the two tRNA molecules form a peptide bond The larger subunit moves forward over the smaller one The smaller subunit rejoins the larger one, this moves the ribosome 3 nucleotides along the mRNA and moves the first tRNA to the E site to be released The second tRNA is now at the P site so that another tRNA with the matching anticodon to the codon on the mRNA can bind to the A site As this process continues, the polypeptide is elongated Once the ribosome reaches the stop codon on the mRNA translation ends and the polypeptide is released Many ribosomes can translate a single mRNA at the same time, these groups of ribosomes are called polysomes

Explain the process of DNA replication in prokaryotes, including the role of enzymes (helicase, DNA polymerase, RNA primase and DNA ligase), Okazaki fragments and deoxynucleoside triphosphates.

Summary: Helicase uncoils the DNA RNA primase adds short sequences of RNA to both strands (the primer) The primer allows DNA polymerase III to bind and start replication DNA polymerase III adds nucleotides to each template strand in a 5'→3' direction These nucleotides are initially deoxyribonucleoside triphosphates but they lose two phosphate groups during the replication process to release energy One strand is replicated in a continuous manner in the same direction as the replication fork (leading strand) The other strand is replicated in fragments (Okazaki fragments) in the opposite direction (lagging strand) DNA polymerase I removes the RNA primers and replaces them with DNA DNA ligase then joins the Okazaki fragments together to form a continuous strand

Distinguish between the sense and antisense strands of DNA.

The antisense strand is the template DNA strand which is transcribed. The sense strand on the other hand is the DNA strand which has the same base sequence as the mRNA with thymine instead or uracil.

What direction is transcription carried out in?

Transcription is carried out in a 5'→3' direction.

What are the stages of translation?

Translation consists of initiation, elongation, translocation and termination.

Explain the process of translation, leading to polypeptide formation.

Translation is the process through which proteins are synthesized. It uses ribosomes, messenger RNA which is composed of codons and transfer RNA which has a triplet of bases called the anticodon. The first stage of translation is the binding of messenger RNA to the small subunit of the ribosome. The transfer RNA's have a specific amino acid attached to them which corresponds to their anticodons. A transfer RNA molecule will bind to the ribosome however it's anticodon must match the codon on the messenger RNA. This is done through complementary base pairing. These two form a hydrogen bond together. Another transfer RNA molecule then bonds. Two transfer RNA molecules can bind at once. Then the two amino acids on the two transfer RNA molecules form a peptide bond. The first transfer RNA then detaches from the ribosome and the second one takes it's place.The ribosome moves along the messenger RNA to the next codon so that another transfer RNA can bind. Again, a peptide bond is formed between the amino acids and this process continues. This forms a polypeptide chain and is the basis of protein synthesis.

What do the 3' and 5' connect to?

the phosphate groups

Transcription

the synthesis of mRNA copied from the DNA base sequences by RNA polymerase.

What is the function of genes?

to specify the sequence of amino acids in a particular polypeptide