DNA Structure and Function I

DNA stands for ___, which is composed of two long polymers of nucleotides (‘strands’)

deoxyribonucleic acid

Each DNA strand has four types of __

nucleotides

a nucleotide has a ___, ___, and ___base

phosphate, sugar, nitrogenous

the two strands of DNA are held together by __ bonds between base pairs. (bases by covalent)

hydrogen

the two strands have polarity and are ___ to each other (5’ to 3’ and 3’ to 5’)

anti-parallel

Ribose and Deoxyribose are __(5 C-atoms) sugars!

Pentose

Each number of the sugar is followed by a ___ , therefore one speaks of 5’, 4’, 3’ carbon.

prime mark

Bases are Nitrogen-containing Ring Compounds of either ___ or ___

Pyrimidines (uracil, cytosine, thymine) or Purines (adenine and guanine)

__ and __: Purine (2 rings)

Adenine and Guanine

___ and ___: Pyrimidine (1 ring)

Cytosine and Thymine

Chargaff postulated that in any DNA strand:

1.  Number of __ bases (A,G) = the number of __bases (T,C).

2. Number of Thymine = Adenosine  Guanine = Cytosine

purine = pyrimidine

However the relative __ of AT pairs to GC pairs for each species can be different!

ratio

purines pair with pyrimidines through hydrogen bonds between __ and __ groups

amino and carbonyl

__ bonds (strong covalent) link nucleotides together

Phosphodiester

the 5’ phosphate (-PO4) links to the 3’ __ (-OH)

hydroxyl

the helix contains two grooves:

major and minor

DNA encodes information in the sequence of __

nucleotides

A, C, G and T is a four-letter alphabet encoding ___

proteins

the 4 nucleotides encode for the __ amino acids of proteins, which is known as the _

20 , genetic code

the complete set of information of an organism’s DNA is called its ___

genome

eukaryotic DNA is packed into __ to help conserve space (and to help nuclei divide during mitosis/meiosis)

discrete chromosomes

humans have two sets of 23 chromosomes containing ___ base pairs

3.2 x 10^9 (3 billion)

the DNA in combination with the organization proteins is called __

chromatin

in humans, chromosome pairs (maternal and paternal) are called __ chromosomes

homologous

__ chromosomes in males (XY) are the only non-homologs

sex

A __is an artificial arrangement of chromosomes

karyotype

chromosomes are different sizes and have varying __ positions (see red lines)

centromere

a __ is a segment of DNA that contains instructions (the code) for making a protein

gene

the number of genes in an organism roughly correlates to its relative __

complexity

___ genes in humans

25,000

In general, the more “ complex” an organism, the larger its __, but there are lots of exceptions

genome

Interphase: chromosomes are “ __ ” to allow for gene expression

unpacked

M ( __ ) Phase: chromosomes are “packed” to allow orderly distribution to daughter cells

mitotic

When cells are NOT actively replicating, their DNA is less compacted and are called the __ chromosomes

interphase

During cell replication, the chromosome is condensed and compacted, turning into a __ chromosome

mitotic

Human chromosome 22 contains __ base pairs (bp), which would extend about 1.5 cm

48 million

During mitosis, chromosome 22 is only 2 μm in length (__ more compact)

10,000X

Two types of proteins that aid in compaction are called __ and non-__

histones

The protein and DNA combination is called __

chromatin

__ histones form a protein “__“ 

8 : bead

DNA coils around these beads, forming a ___, which is the most fundamental level of chromatin packing

nucleosome

The ___ is __charged, enabling it to bind to the negatively charged sugar-phosphate DNA backbone

histone octamer : positively

Why the core histone proteins have a high portion of positive charged amino acids?

1. Each of the core histones has a N-terminal amino acid “__ “

2. Modifications at the tail control __

1. tail

2. chromatin structure

__ use ATP hydrolysis to slide DNA around a histone

Chromatin-remodeling complexes