ch. 16: molecular basis of inheritance

Gene (classical definition)

a particulate unit of inheritance

Gene (molecular definition)

a segment of nucleic acid which codes for a product (a protein or an RNA)

What are 2 types of nucleic acids?

DNA and RNA

What 3 things does each nucleotide consist of?

a sugar molecule, a phosphate group, a nitrogenous base

What is a nucleic acid made of?

polymers of nucleotides

What sugar molecule is in DNA?

deoxyribose

What sugar molecule is in RNA?

ribose

True or false, the phosphate group is the same in DNA and RNA.

true

What 4 nitrogenous bases are in DNA?

guanine, cytosine, adenine, thymine

What 4 nitrogenous bases are in RNA?

guanine, cytosine, adenine, uracil

3’ end (three prime end)

OH on carbon #3 of sugar molecule

5’ end (five prime end)

phosphate on carbon #5 of sugar molecule

What forms the double helix of the DNA structure?

two nucleotide polymers held together by hydrogen bonds between complementary bases

What holds together the two nucleotide polymers to form the double helix strucutre?

hydrogen bonds

What is the complementary base for guanine in DNA?

cytosine

What is the complementary base for cytosine in DNA?

guanine

What is the complementary base for thymine in DNA?

adenine

What is the complementary base for adenine in DNA?

thymine

What is the complementary base for cytosine in RNA?

guanine

What is the complementary base for guanine in RNA?

cytosine

What is the complementary base for adenine in RNA?

uracil

What is the complementary base for thymine in RNA?

adenine

What phase does DNA replication occur during the cell cycle?

S-phase

What is the process for DNA replication? (6)

helicase unwinds the double helix. primase produces a small RNA primer on each strand at the origin of replication. DNA polymerase extends the primers using only bases complementary to the DNA template. leading strand is replicated continuously. lagging strand is replicated in okazaki fragments and ligase seals the fragments together.

What is the result of DNA replication?

two double helix molecules, each identical to each other and to the original double helix.

During DNA replication, what unwinds the double helix?

helicase

During DNA replication, what does primase do?

it produces a small RNA primer

During DNA replication, where does primase produce?

on each strand at the origin of replication

During DNA replication, what does DNA polymerase use to extend primers?

uses only bases complementary to the DNA template

During DNA replication, DNA polymerase can only extend where?

3’ end of an existing nucleic acid

How accurate is DNA polymerase in matching complementary base pairs?

99.999%

During DNA replication, what 2 things does DNA polymerase do?

extend primers using only bases complementary to the DNA template and have a built-in proof-reading enzyme to correct mistakes

Why is the error rate of DNA replication 1 in 10 million?

DNA polymerase has a built-in proof-reading enzyme to correct its mistakes

Okazaki fragments

fragments replicated from the lagging strand

During DNA replication, what does ligase do?

it seals the okazaki fragments together

What is the difference between the leading and lagging strand replication process?

leading strand is replicated continuously, lagging strand is replicated in fragments

How are the two strands of the double helix positioned?

must be antiparallel

DNA replication is important to which life characteristic?

basis of heredity

Semi-conservative replication

product is half an old strand and half a newly constructed strand

Are the two resulting double helixes made of two new strands or one old and one new or fragments of an old strand scattered about within a new strand?

one old and one new

Why does DNA replication cause chromosomes to get shorter over time?

DNA polymerase can only add nucleotides to 3’ end of existing strand, can’t fully replicate the 5’ ends. leaves a small section unreplicated with each division which gradually shortens the chromosome

How do prokaryotes avoid the issue of DNA replication at the 5’ end?

they have circular chromosomes

How do eukaryotes avoid the issue of DNA replication at the 5’ end?

use telomeres and telomerase

Telomere

a repeating sequence found at both ends of eukaryotic chromosomes

What can happen to telomere length?

may shorten by a few repeats of each cell division, limiting the life-span of the cell line

Telomerase

an enzyme which can use its own internal RNA as a template to extend the length of telomeres

What is the importance of the relationship between telomere and telomerase?

telomerase overcomes the limits to cell division imposed by the telomere

Histones

proteins which DNA wraps around

Nucleosomes

formed by DNA wrapping around histones

How are highly condensed chromosomes formed?

DNA folds around additional structures

When are highly condensed chromosomes formed?

cell division

Euchromatin

genomes that condense only for cell division

Heterochromatin

genomes that remain in a highly condense state outside of cell division