DNA Replication Flashcards
4.1.1. Understand that DNA is a double stranded molecule that occurs bound to proteins (histones) in chromosomes in the nucleus, and as unbound circular DNA in the cytosol of prokaryotes, and in the mitochondria and chlorplasts of eukaryotic cells.
Describe the six main components of the eukaryotic chromosome structure.
DNA is tightly packed to fit into the nucleus by
1). DNA is wrapped around histone proteins. Histones are a family of basic proteins that associate with DNA in the nucleus and help condense it into chromatin.
2) The combines loop of DNA and 8 histones is called a nucleosome
3). Nucleosomes are packaged into thread called chromatin. This locks away DNA so it can’t be copied.
4) Linear threads of chromatin form chromosomes.
5) During cell division, chromatin is looped and coiled to form X shape.
6) At other times, DNA is pacaged less tightly. Instead, the linear chromosones are long, invisible threads.
Understand that DNA is a double stranded molecule that occurs bound to proteins (histones) in chromosomes in the nucleus, and as unbound circular DNA in the cytosol of prokaryotes, and in the mitochondria and chlorplasts of eukaryotic cells.
Explain why eukaryotic DNA needs to be packaged up to fit inside a cell nucleus.
DNA is a very long molecule. If it was not packaged up it could not fit into the nucleus and it could not properly be organised for replication.
Understand that DNA is a double stranded molecule that occurs bound to proteins (histones) in chromosomes in the nucleus, and as unbound circular DNA in the cytosol of prokaryotes, and in the mitochondria and chlorplasts of eukaryotic cells.
How do histone protiens help in the coiling up of DNA.
Histones provide a mutli-unit strcuture for the DNA to wrap around in an organised way so that it takes up les space in the nucelus than if it was spread out. Without histones, DNA would not have its compact, double-helix structure and would be too long to fit inside the chromosomes in a cell’s nucleus. This means that genetic material could not pass on to other cells without histones. Histones prevent DNA from becoming tangled and protect it from DNA damage. In addition, histones play important roles in gene regulation and DNA replication. Without histones, unwound DNA in chromosomes would be very long.
Understand that DNA is a double stranded molecule that occurs bound to proteins (histones) in chromosomes in the nucleus, and as unbound circular DNA in the cytosol of prokaryotes, and in the mitochondria and chlorplasts of eukaryotic cells.
Suggest why a cell coils up its chromosomes into tight strcutures when it is going to divide.
Coiling the chromosomes into tight structure helps the cell maintain order and ensures proper segregation of the chromosomes during mitosis and cell division.
Understand that DNA is a double stranded molecule that occurs bound to proteins (histones) in chromosomes in the nucleus, and as unbound circular DNA in the cytosol of prokaryotes, and in the mitochondria and chlorplasts of eukaryotic cells.
Describe the prokaryotic chromosome structure.
In prokaryotes (eg. Bacteria) DNA is:
1.) single chromosome
2.) circular, double-stranded
3.) not bound to histones
4.) found in cytoplasm
Understand that DNA is a double stranded molecule that occurs bound to proteins (histones) in chromosomes in the nucleus, and as unbound circular DNA in the cytosol of prokaryotes, and in the mitochondria and chlorplasts of eukaryotic cells.
Compare the prokaryotic and eukaryotic chromosome structure.
In prokaryotes, the circular chromosome is contained in the cytoplasm in an area called the nucleoid. In contrast, in eukaryotes, all of the cell’s chromosomes are stored inside a structure called the nucleus. Each eukaryotic chromosome is composed of DNA coiled and condensed around nuclear proteins called histones. The chemical composition and structural organization of DNA is similar in both prokaryotes and eukaryotes. In both prokaryotes and eukaryotes, the expression of genetic material is facilitated by transcription and translation.
Eukaryotic Chromosome Prokaryotic Chromosome SIn prokaryotes, the circular chromosome is contained in the cytoplasm in an area called the nucleoid. In contrast, in eukaryotes, all of the cell's chromosomes are stored inside a structure called the nucleus. Each eukaryotic chromosome is composed of DNA coiled and condensed around nuclear proteins called histones. The chemical composition and structural organization of DNA is similar in both prokaryotes and eukaryotes. In both prokaryotes and eukaryotes, the expression of genetic material is facilitated by transcription and translation.
Understand that DNA is a double stranded molecule that occurs bound to proteins (histones) in chromosomes in the nucleus, and as unbound circular DNA in the cytosol of prokaryotes, and in the mitochondria and chlorplasts of eukaryotic cells.
Describe the mitochondria and chloroplast DNA.
Mitochondrial DNA and chloroplast DNA is:
circular, double stranded
found within these organelles
not bound to histones
contain the genes for proteins, as well as tRNA and rRNAs
4.1.2. Recall the strcuture of DNA, including:
a). nucleotide composition
b). complementary base pairing and
c). weak, base-specific hydrogen bonds between DNA strands
Recall the structure of DNA and RNA and compare them.
Nucleic acids are the macromolecules that make up the genetic materail of all living organsims. There are two types:
1). Deoxyribonucleic acid
2). Ribonucleic acid
Each nucleic acid is made up of a chain of nucleotides. Each nucleotide consists of:
sugar (5-carbon) ring (called deoxyribise in DNA; ribose in RNA)
A phosphate
A nitrogenous base (there are 5 different types, A, C, G, T in DNA) (but T is replaced by U in RNA).
In formation of a nucleotide, a phosphoric acid and a base are chemically bonded to a sugar moleculre by condensation reactions in which water is given off. The reverse reaction is hydrolysis.
4.1.2. Recall the strcuture of DNA, including:
a). nucleotide composition
b). complementary base pairing and
c). weak, base-specific hydrogen bonds between DNA strands
How can simple nucleotide units combone to store genetic information?
The nucleotides (bases) are stored in a specific sequence (able to be read by the cellular machinary) that codes for amino acids that make proteins.
4.1.2. Recall the strcuture of DNA, including:
a). nucleotide composition
b). complementary base pairing and
c). weak, base-specific hydrogen bonds between DNA strands
Describe the double stranded structure of the DNA.
The phosphate of one nucelotide bonds to the sugar ring of the next nulceotide to form a sugar-phosphate backbone. This gives the DNA molecule an asymmetrical strcuture.
The two strands in DNA are held together by the complementary base-specific pairing of nitrogen bases between adjacent strands using weak hydrogen bonds.
The strands run in opposite direction to the other. The ends of a DNA strand are labelled 5’ and 3’ ends. The 5’ end has a terminal phosphate group, the 3’ end has a terminal hydroxylm group.
4.1.3 Explain the role of helicase (in terms of unwinding the double helix and separation of the strands) and DNA polymerase (in terms of formation of the new complementary strands) in ythe process of DNA replication. References should be made to the direction of replication.
Reference the direction of the two DNA strands.
The carbon atoms on the pentose sugar are labelled 1-5. During DNA replication new nucleotides are added to the 3’ end, the third carbon, o fthe existing nucleotide chain. It is therefore said DNA replication works in the 5’ to 3’ direction. Each nucleaotide on the complementary strand is reversed. The strands run 5’ to 3’ on left and 3’ to 5’ on right. They are termed anti-parallel.
DNA polymerase can only add nucleotides to the 3’ OH group of the growing DNA strand, this is why DNA replication occurs only in the 5’ to 3’ direction. In the DNA double helix, the two joined strands run in opposite directions, thus allowing base pairing between them, a feature that is essential for both replication and transcription of the genetic information
4.1.3 Explain the role of helicase (in terms of unwinding the double helix and separation of the strands) and DNA polymerase (in terms of formation of the new complementary strands) in ythe process of DNA replication. References should be made to the direction of replication.
Why do the DNA strands have an asymmetrical structure?
The sugar and phosphate linkages 3’ to 5’ creates asymmetry, giving the molecule a direction so that the two strands are anti-parallel.
4.1.3 Explain the role of helicase (in terms of unwinding the double helix and separation of the strands) and DNA polymerase (in terms of formation of the new complementary strands) in ythe process of DNA replication. References should be made to the direction of replication.
Compare and Contrast DNA and RNA structure.
DNA RNA
Sugar Present Deoxyribose Ribose
Bases Present A, G, C, T A, G, C, U
Number of strands Two (double) One (single)
Relative length Long Short
4.1.3 Explain the role of helicase (in terms of unwinding the double helix and separation of the strands) and DNA polymerase (in terms of formation of the new complementary strands) in ythe process of DNA replication. References should be made to the direction of replication.
Explain the role of the helicase and DNA polymerase in DNA replication.
Before cells can divide, the DNA needs to be replicated so that there is enough to split between two daughter cells. This process of replication involves two enzymes:
Helicase and DNA polymerase.
DNA helicase “unzips” the two strands by unwinding the helix and breaking the weak hydrogen bonds between the two complemenatry strands. This creates a replication fork so that the nucleotides are exposed. It untwists the double helix and separates the two DNA strands. -By pulling apart and untwisting the DNA strands, helicase makes them available for replication. DNA polymerase uses each original DNA strand as a template to produce a copy of the DNA molecule. It adds complementary nucleotides to the exposed nucleotides on each original strand. Due to the directionality of the DNA, one new strand can be synthesised in a continuous leading strand. The other strand is synthesised in sections that are fused by the enzyme ligase as replication continues. DNA polymerase also proofreads the newly synthesised DNA strand to check for errors.
